MOTOR VEHICLE COMPRISING EXHAUST THERMAL PROTECTION BY ENGINE TORQUE RESTRICTION, METHOD AND PROGRAM BASED ON SUCH A VEHICLE

Abstract

The invention relates to a motor vehicle comprising a heat engine, an exhaust line, and a thermal protection system which comprises: - a means for evaluating the temperature of the exhaust line (M1); - a means for evaluating temperature criticality (M2) between a low level 1 without risk of degradation of the components of the exhaust line; an intermediate level 2; and a high level 3 with said risk; - a means for cooling (M3) the heat engine above level 2 so as not to degrade the performance of the heat engine; and - a limiting means (M4) limiting the heat engine above level 3, by limiting the torque of the heat engine in the event of overheating of the exhaust line. The invention also relates to a method and a program based on such a vehicle. Figure 1

Description

Title of the invention: MOTOR VEHICLE COMPRISING EXHAUST THERMAL PROTECTION BY ENGINE TORQUE RESTRICTION, METHOD AND PROGRAM BASED ON SUCH A VEHICLE

[0001] The invention relates to the field of thermal protection of the components of an exhaust line of a motor vehicle gasoline engine.

[0002] New gasoline engines for motor vehicles must meet the requirements of emission standards, such as the new standard known as "Euro 6eBis", which is more stringent than the previous standard, known as "Euroôe".

[0003] The extended test conditions of this new Euro 6eBis standard imply not using enrichment of the petrol / air mixture to cool the components of the exhaust line.

[0004] A gasoline engine suitable for the Euroô standard operates at a first richness level (level 1). But if during a long or heavy full load, the temperature of the exhaust line components is considered critical, it is admitted, known and accepted to increase the fuel richness of the gasoline / air mixture (therefore leaving the richness level 1 temporarily) to cool and protect the exhaust line components.

[0005] However, with this new Euro 6eBis regulation, this process of increasing the fuel richness of the petrol / air mixture is no longer possible without risking exceeding the emissions targets.

[0006] This requires either redesigning the exhaust line components of gasoline engines or implementing a cooling strategy.

[0007] As this EuroôeBis standard is applicable soon, a redesign of the exhaust line components does not seem possible at this time; and this would involve losses of time and materials given the imminent arrival of a new Euro7 standard, which requires a redesign of certain components (including the exhaust line).

[0008] The objective of the invention is to overcome the defects of the prior art, and in particular to propose a solution for cooling the exhaust line while limiting emissions, and on the basis of the current components of gasoline vehicles.

[0009] To achieve this objective, the invention proposes a motor vehicle comprising a heat engine, an exhaust line, and a thermal protection system which comprises: - a means of evaluating the temperature of the exhaust line, determining an exhaust line temperature value; - a means of temperature criticality assessment determining a temperature criticality level of the exhaust line between a low level 1 without risk of degradation of the exhaust line components; an intermediate level 2 above level 1; and a high level 3 above level 2, with risk of irreversible degradation of the exhaust line components; - a cooling means for cooling the heat engine when the temperature reaches or exceeds level 2 so that the heat engine is cooled without degrading the performance of the heat engine; and - a means of limiting the thermal engine if the temperature of the exhaust line reaches or exceeds level 3, by limiting the torque of the thermal engine in the event of overheating of the exhaust line.

[0010] Advantageously, the invention makes it possible to avoid redesigning the components of the exhaust line of gasoline engines; to ensure the integrity of the components of the exhaust line; to avoid the risk of fire in the vehicle; to avoid the use of an adjustment limiting the performance of the powertrain.

[0011] The invention therefore makes it possible, to this extent, to ensure the safety of users and the vehicle with regard to the risk of fire.

[0012] According to a variant, the temperature evaluation means comprises a sensor arranged on the exhaust line.

[0013] This makes it possible to simply determine the temperature of the exhaust line, in particular of the exhaust manifold, in order to implement the invention.

[0014] According to a variant, the temperature evaluation means comprises a calculator and a temperature calculation model based on exhaust line usage data.

[0015] This makes it possible to calculate and anticipate the temperature of the exhaust line, in particular of the exhaust manifold.

[0016] According to a variant, the limiting means limits a control instruction of the computer by around 20% to 30% of the torque while maintaining the performance of the engine.

[0017] This makes it easy to restrict the engine and limit overheating, with acceptable engine performance.

[0018] According to a variant, the thermal protection system comprises an occurrence counter counting the number of occurrences of the clamping, in particular the number of occurrences of the clamping per driving cycle.

[0019] This makes it possible to track the number of engine overheats per vehicle start cycle, and to facilitate diagnosis by maintenance services.

[0020] According to a variant, the temperature criticality evaluation means determines a temperature criticality level based on a critical threshold beyond which the elements of the exhaust line undergo irreversible degradation, level 3 corresponding to 85 to 90% of the critical threshold, and level 2 corresponding to 75 to 80% of the critical threshold.

[0021] This makes it possible to calibrate the levels while maintaining a known objective margin in relation to the critical threshold of degradation of the materials of the exhaust line, in particular of the exhaust line manifold.

[0022] According to a variant, the motor vehicle comprises a first heat transfer circuit, and the cooling means comprises a second heat transfer circuit cooling the thermal engine, and a motor-fan unit connecting the second heat transfer circuit to the first heat transfer circuit, via a water outlet housing.

[0023] This allows the engine to be cooled in the event that overheating of the exhaust line, in particular the exhaust manifold, is detected.

[0024] According to a variant, the exhaust line comprises an exhaust manifold, characterized in that said temperature and components of the exhaust line designate the temperature and components of the exhaust manifold.

[0025] This allows the exhaust manifold of the exhaust line to be specifically protected.

[0026] The invention further relates to a method for thermally protecting an exhaust line of a motor vehicle according to the invention, the protection method comprising the following steps: - a step of evaluating the temperature of the exhaust line, determining a temperature value of the exhaust line; - a temperature criticality assessment step, determining a temperature criticality level of the exhaust line between a low level 1 without risk of degradation of the exhaust line components; an intermediate level 2 above level 1; and a high level 3 above level 2, with risk of irreversible degradation of the exhaust line components; - a cooling step to cool the heat engine when the temperature reaches or exceeds level 2 so that the heat engine is cooled without degrading the performance of the heat engine; and - a limiting step restricting the thermal engine if the temperature of the exhaust line reaches or exceeds level 3, by limiting the torque of the thermal engine in the event of overheating of the exhaust line.

[0027] Another object of the invention relates to a computer program comprising program code instructions for executing the steps of the thermal protection method according to the invention, when said program operates on a computer.

[0028] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the attached [Fig.l] illustrating the thermal protection system and method according to a preferred embodiment of the invention.

[0029] The invention relates to a strategy for gasoline engines meeting the Euro 6eBis standard by limiting the torque of the gasoline engine in cases of overheating in the exhaust manifold.

[0030] Regarding the determination of the temperature level of the exhaust manifold, there are two possibilities for recovering this information: - the simplest solution is to install a temperature sensor on the exhaust manifold (or on one of the components of the exhaust line); - the most complex solution is to use the information available in an engine computer to estimate the temperature in the exhaust manifold.

[0031] The engine computer receives, for example, the following information: - the air temperature in the air inlet manifold (denoted To); - the temperature in the air intake distributor (denoted T2s); - the flow rate (at the flow meter) of the intake (noted Qair) or reconstructed from the intake distributor pressure; - the crankshaft speed (from the engine speed sensor) (noted Rmot); - the temperature of the cooling water in the heat transfer circuit of the gasoline thermal engine (denoted Teau); - the torque level of the thermal engine at the crankshaft (noted Cmot) - the boost pressure; - the position of the phase shifters; - ignition advance; - the value of the current click adaptation.

[0032] Thanks to measurements in the engine cabin with scans of the previous parameters (in particular To, T2s, Qair, Rmot, Teau and Cmot), during the development phase of the gasoline thermal engine, a model is developed to estimate the temperature in the exhaust manifold.

[0033] Now concerning the development of the different levels of temperature criticality, the inventors have implemented a strategy for thermal protection of the exhaust manifold (and more broadly of the components of the exhaust line) in 3 levels: - Level 1 of “normal condition”: normal operating condition without risk of degradation of the exhaust line components; - Level 2 of "engine cooling procedure without user discomfort": this is a temperature level higher than level 1, therefore presenting a risk to the integrity of the exhaust line components. Thus, we seek to reduce the temperature in the exhaust line without degrading the performance of the gasoline thermal engine from the driver's point of view; - Level 3 of "engine torque reduction" (therefore with driver alert): the temperature of the exhaust manifold is too high, we enter into a tougher protection strategy constraining the driver's will by restricting the torque of the thermal engine. This allows the temperature in the vehicle's exhaust line to be reduced to protect the integrity of the exhaust line components and mainly the exhaust manifold.

[0034] A counter is also provided for the number of occurrences of this restriction on the same cycle between switching on and switching off the engine.

[0035] Now concerning the detail of the strategy for each temperature criticality level: - At level 1: there are no restrictions, the engine is in normal operating condition; - At level 2: the aim is to reduce the temperature in the exhaust line, without the driver being bothered or noticing it. To achieve this, the aim is to increase engine cooling by activating the motor-fan unit and connecting the heat transfer circuit of the thermal engine to the vehicle's heat transfer circuit via the water outlet housing (optionally, the fluid flow rate in the engine's heat transfer circuit is also increased); - At level 3: we seek to reduce the temperature in the exhaust line without worrying about an impact or not on the driver's wishes, to reduce the heat in the exhaust line as much as possible.

[0036] At level 3, the torque of the thermal engine is then restricted (by restricting the control instruction coming from the engine computer) by around 20% to 30% of the torque compared to the driver's wishes, while seeking to limit the torque as much as necessary. And the torque is restored as soon as possible to minimize the perception of a drop in performance from the driver's point of view. The restitution will not be carried out during the same torque demand phase (because this would be theoretically impossible given the fact that there is a need for a relaxation time), in order not to generate excess torque for the driver for a given level of pedal stress.

[0037] This torque restriction level is calibrated during the function development phase and may be different depending on the type of engine.

[0038] The counter makes it possible to count the number of occurrences of torque restriction on an exhaust line overheating alert. This counter is preferably reset to 0 when the vehicle is started, and we have an occurrence threshold (named “ThresholdTh”) on this counter at a calibratable value when developing this function, for example at the value of 20 iterations.

[0039] Thus, each time the engine computer detects overheating of the exhaust line that said computer must process by restricting the engine torque, this counter is incremented by 1. And when the counter reaches the occurrence threshold level SeuilTh, a fault code is stored in its read-only memory and the engine computer communicates it to the service box, to indicate to the maintenance service that the engine computer has encountered a certain number of overheating problems at the exhaust line level over the same driving cycle.

[0040] This fault code clearing is completely transparent to the driver. The only thing the driver can notice is the loss of torque compared to his wishes.

[0041] Now concerning the development of the temperature thresholds, for each level, a critical temperature of the components of the exhaust line is determined (by the method described below) from which the integrity of the components is no longer assured, which gives the limit “critical temperature threshold” which will be called here STcrit. This level STcrit is measured by testing during the development of the function.

[0042] Once this STcrit threshold has been determined by tests on a material bench or by tests on an engine bench, a level 3 trigger coefficient is determined by tests, this coefficient being calibrated in the function when developing this function.

[0043] The order of magnitude of this coefficient is for example in the range 85%-90% of the STcrit threshold, that is to say that level 3 is triggered when the estimated or measured temperature in the exhaust manifold reaches between 85% and 90% of the STcrit threshold.

[0044] Then, a trigger coefficient of level 2 is determined by testing, this coefficient being calibrated in the function when developing this function. The order of magnitude of this coefficient is for example in the range 75%-80% of the STcrit threshold, that is to say that level 2 is triggered when the estimated or measured temperature in the exhaust manifold reaches between 75% and 80% of the STcrit threshold.

[0045] The critical temperature threshold in the exhaust line depends on the components that make up the exhaust line, the material used for these components, the distance of these components from the combustion chamber and the level of ventilation of these components, therefore their positioning relative to the air flows when the vehicle is moving.

[0046] The critical temperature threshold (STcrit) is determined so that below it, when the temperature level returns to normal, the characteristics of the components of the exhaust line return to the same physicochemical properties as before the temperature rise in the exhaust line. The critical temperature threshold is the level above which the components of the exhaust line suffer irreversible damage.

[0047] When the exhaust line is in level 1 or 2, there is no need to have a recovery function.

[0048] The recovery function only concerns level 3.

[0049] Once level 3 is reached, the engine computer enters recovery mode when the estimated or measured temperature in the exhaust manifold leaves level 3 and returns to level 2 (alternatively, recovery may occur when the estimated or measured temperature in the exhaust manifold leaves level 3 and returns to level 1).

[0050] This restoration includes the following. The engine computer stops the torque restriction of the gasoline engine, i.e. it allows the full torque potential of the engine again.

[0051] The only thing that remains from this switch to "torque restriction" mode is possibly the fault code stored in the ROM memory of the engine computer, if during a run the torque restriction counter, due to overheating phenomena of the exhaust line, has exceeded the occurrence threshold SeuilTh. Thus, the maintenance service can identify that the thermal engine has suffered a significant number of overheatings at the level of its exhaust line. However, this fault code does not remain in the "permanent" state in the memory of the computers, but the fault code changes to the "transient" state to indicate to the maintenance service that the fault has resolved itself.

[0052] The invention further relates to a corresponding thermal protection method and program. The program can be loaded into a motor vehicle controller or a thermal engine controller.

Claims

Claims

1. Motor vehicle comprising a heat engine, an exhaust line, and a thermal protection system which comprises: - a means for evaluating the temperature of the exhaust line (M1), determining a temperature value of the exhaust line; - a means for evaluating temperature criticality (M2) determining a criticality level of the temperature of the exhaust line between a low level 1 without risk of degradation of the components of the exhaust line; an intermediate level 2 above level 1; and a high level 3 above level 2, with risk of irreversible degradation of the components of the exhaust line; - a cooling means (M3) for cooling the heat engine when the temperature reaches or even exceeds level 2 so that the heat engine is cooled without degrading the performance of the heat engine;and - a limiting means (M4) limiting the thermal engine if the temperature of the exhaust line reaches or even exceeds level 3, by limiting the torque of the thermal engine in the event of overheating of the exhaust line.;

2. Motor vehicle according to claim 1, characterized in that the temperature evaluation means (Ml) comprises a sensor arranged on the exhaust line.

3. Motor vehicle according to claim 1, characterized in that the temperature evaluation means (Ml) comprises a calculator and a temperature calculation model from exhaust line usage data.

4. Motor vehicle according to any one of claims 1 to 3, characterized in that the thermal protection system comprises an occurrence counter counting the number of occurrences of the restriction, in particular the number of occurrences of the restriction per driving cycle.

5. Motor vehicle according to any one of claims 1 to 4, characterized in that the temperature criticality evaluation means (M2) determines a temperature criticality level as a function of a critical threshold beyond which the elements of the exhaust line undergo irreversible degradation, level 3 corresponding to 85 to 90% of the critical threshold, and level 2 corresponding to 75 to 80% of the critical threshold.

6. Motor vehicle according to any one of claims 1 to 5, comprising a first heat transfer circuit, characterized in that the cooling means (M3) comprises a second heat transfer circuit cooling the heat engine, and a motor-fan unit connecting the second heat transfer circuit to the first heat transfer circuit, via a water outlet housing.

7. A motor vehicle according to any one of claims 1 to 6, wherein the exhaust line comprises an exhaust manifold, characterized in that said temperature and components of the exhaust line designate the temperature and components of the exhaust manifold.

8. A method for thermally protecting an exhaust line of a motor vehicle according to any one of claims 1 to 7, the protection method comprising the following steps: - a step of evaluating the temperature of the exhaust line (El), determining a temperature value of the exhaust line; - a step of evaluating temperature criticality (E2), determining a criticality level of the temperature of the exhaust line between a low level 1 without risk of degradation of the components of the exhaust line; an intermediate level 2 above level 1; and a high level 3 above level 2, with risk of irreversible degradation of the components of the exhaust line; - a cooling step (E3) for cooling the heat engine when the temperature reaches or even exceeds level 2 so that the heat engine is cooled without degrading the performance of the heat engine;and - a limiting step (E4) limiting the thermal engine if the temperature of the exhaust line reaches or even exceeds level 3, by limiting the torque of the thermal engine in the event of overheating of the exhaust line.;

9. A computer program comprising program code instructions for carrying out the steps of the thermal protection method according to claim 8, when said program is running on a computer.

Images