Method for operating an internal combustion engine with overrun cut-off

Abstract

Method for operating an internal combustion engine (1) with overrun cut-off, in which a fuel supply to the internal combustion engine (1) is interrupted by a control device (4) of the internal combustion engine (1), wherein a current speed of the internal combustion engine (1) is detected at an input of an automatic transmission (2) and evaluated by the control device (4), wherein the control device (4) determines a current speed gradient of the internal combustion engine (1) from the detected speeds and estimates the duration of the next overrun cut-off process of the internal combustion engine (1) therefrom, wherein the control device (4) prevents the overrun cut-off of the internal combustion engine (1) and maintains the fuel supply to the internal combustion engine (1) if the estimated duration of the next overrun cut-off process of the internal combustion engine (1) falls below a specified or specifiable threshold value of a minimum overrun cut-off duration,and wherein the fuel supply to the internal combustion engine (1) is reactivated by the control device (4) after the end of an overrun cut-off process, wherein a renewed overrun cut-off is prevented by the control device (4) at least until a specified or specifiable minimum duration is reached again depending on the current gear of the automatic transmission (2) and the speed of the internal combustion engine (1).

Description

[0001] The present invention relates to a method for operating an internal combustion engine with overrun fuel cut-off.

[0002] An important task in the development of internal combustion engines is to save fuel through suitable technical measures and thus also reduce pollutant emissions. For this purpose, internal combustion engines often feature a so-called overrun cut-off system, which is activated in certain driving situations. If the vehicle's accelerator pedal is not depressed during an overrun phase and the current engine speed is above a so-called reactivation speed, the overrun cut-off is activated by a control device of the internal combustion engine interrupting the fuel supply to the internal combustion engine in order to stop the combustion process of the fuel-air mixture and save fuel.When the current speed of the internal combustion engine subsequently drops back to the restart speed, the fuel supply is reactivated by means of the control device so that a combustion process of the fuel-air mixture within the internal combustion engine occurs again.

[0003] Particularly during heavily braked overrun downshifts, automatic transmissions often experience short overrun cut-off phases, typically lasting less than one second, due to the short time between the overrun downshifts. However, these overrun cut-off phases are sufficient to flood a catalytic converter of a motor vehicle's exhaust aftertreatment system with oxygen. This oxygen flooding of the catalytic converter, which may comprise at least one three-way catalytic converter, results in the increased oxygen content preventing nitrogen oxide emissions from the internal combustion engine from being converted. In order for the nitrogen oxide conversion of the catalytic converter to be reactivated, it is necessary to "clear" the catalytic converter using a rich fuel-air mixture (combustion air ratio < 1).

[0004] Consequently, short overrun cut-off processes are neither advantageous from a fuel consumption nor from an emissions perspective due to the subsequent "catalytic converter clearing" with a rich fuel-air mixture. Depending on the gearshift, the combustion process of the fuel-air mixture within the internal combustion engine must be reactivated before the gearshift, which also results in corresponding comfort disadvantages.

[0005] To remedy the aforementioned problems, it is known from the prior art, for example, to shift the reactivation speed depending on the brake pressure. However, this has various disadvantages, such as a brief reactivation of the combustion process of the fuel-air mixture within the internal combustion engine during a brief braking operation, independent of shifting operations of the automatic transmission.

[0006] DE 33 37 786 A1 discloses a control system for the overrun operation of an internal combustion engine as a function of a current engine speed and a restart engine speed threshold curve. Furthermore, this document also discloses means for suppressing overrun cutoff in the event of predefined events.

[0007] DE 10 2022 200 251 A1 discloses a method for operating an internal combustion engine in which, during an overrun cutoff, the fuel supply to the internal combustion engine is interrupted by a control device. The current engine speed is detected and evaluated by the control device. Furthermore, the engine speed gradient (change in speed) is determined. This serves as the basis for calculating the expected duration of the next overrun cutoff. The control device prevents the engine from overrunning if the estimated duration of the next overrun cutoff falls below a specified threshold value for a minimum overrun cutoff duration.

[0008] DE 10 2012 216 543 A1 discloses a further method for operating an internal combustion engine in which an overrun cut-off is activated or suppressed depending on the predicted duration

[0009] The invention aims to provide a further improved method for operating an internal combustion engine with overrun cut-off.

[0010] The solution to this problem is provided by a method for operating an internal combustion engine with overrun cut-off having the features of claim 1. The subclaims relate to advantageous developments of the invention.

[0011] In a method according to the invention for operating an internal combustion engine with overrun cut-off, in which a fuel supply to the internal combustion engine is interrupted by a control device of the internal combustion engine, it is provided that a current speed of the internal combustion engine is detected at an input of an automatic transmission and evaluated by the control device, wherein the control device determines a current speed gradient of the internal combustion engine from the detected speeds and estimates the duration of the next overrun cut-off process of the internal combustion engine therefrom, wherein the control device prevents the overrun cut-off of the internal combustion engine and maintains the fuel supply to the internal combustion engine if the estimated duration of the next overrun cut-off process of the internal combustion engine falls below a specified or specifiable threshold value of a minimum overrun cut-off duration,and wherein the fuel supply to the internal combustion engine is reactivated by the control device after the end of an overrun cut-off process, wherein a renewed overrun cut-off is prevented by the control device at least until a specified or definable minimum duration is reached again, depending on the current gear of the automatic transmission and the engine speed. The method according to the invention is based on the finding that a minimum overrun cut-off duration of a few seconds is necessary to compensate for the subsequent increased fuel consumption for the necessary catalyst removal in order to achieve an overall fuel consumption advantage. This minimum overrun cut-off duration can thus be used in the method to prevent the overrun cut-off for efficiency reasons and thus provide an "overrun cut-off prohibition" for the internal combustion engine.

[0012] In an advantageous embodiment, the control device maintains the overrun cutoff of the internal combustion engine and interrupts the fuel supply until the control device receives a request signal from another system or consumer of the motor vehicle to terminate the overrun cutoff of the internal combustion engine. This ensures that the current overrun cutoff phase is utilized to its maximum for efficiency reasons.

[0013] In one embodiment, it is proposed that the fuel supply to the internal combustion engine be controlled by the control device in such a way that no fuel is supplied during overrun downshifts and the combustion process of the fuel-air mixture within the internal combustion engine is not activated. Such an operating strategy may or may not be advantageous depending, for example, on the severity of the current vehicle deceleration, so that the control device preferably also checks whether the vehicle deceleration threshold has been exceeded.Furthermore, various other parameters, such as the current driving mode of the motor vehicle and / or the result of a check as to whether a previous event was identified as an overrun downshift and / or the result of a check as to whether the overrun downshift occurred at most a defined time ago, can be incorporated into the operating strategy of the internal combustion engine, which is implemented by means of the control device.

[0014] Further features and advantages of the present invention will become clear from the following description of a preferred embodiment with reference to the enclosed Fig. 1, which shows parts of a drive train 10 and an exhaust system 11 of a motor vehicle in a schematically highly simplified form.

[0015] The drivetrain 10 comprises an internal combustion engine 1 and an automatic transmission 2, which may in particular be a dual-clutch transmission or a torque converter transmission. The exhaust system 11, which is connected to the internal combustion engine 1, has an exhaust gas aftertreatment device 3, which includes a catalytic converter device 30. The catalytic converter device 30 can, for example, have at least one three-way catalytic converter.

[0016] Furthermore, a control device 4 is provided which is designed to control the operation of the internal combustion engine 1, in particular also the fuel supply to the internal combustion engine 1.

[0017] The internal combustion engine 1 is equipped with an overrun cut-off system that is activated in certain driving situations. If the accelerator pedal of the motor vehicle is not pressed during an overrun phase and the current speed of the internal combustion engine 1 is above a reset speed, the overrun cut-off system is activated by the control device 4 interrupting the fuel supply to the internal combustion engine 1, thereby stopping the combustion process of a fuel-air mixture within the internal combustion engine 1 and thus also saving fuel. When the current speed of the internal combustion engine 1 drops to the reset speed, the fuel supply is reactivated by the control device 4, so that a combustion process of the fuel-air mixture within the internal combustion engine 1 resumes.

[0018] Particularly during heavily braked overrun downshifts, the automatic transmission 2 frequently experiences short overrun cut-off phases, typically lasting less than one second, since there is only a short time between the overrun downshifts. However, these overrun cut-off phases are already sufficient to flood the catalytic converter device 30 of the exhaust gas aftertreatment device 3 with oxygen. This oxygen flooding of the catalytic converter device 30 leads, in particular, to the nitrogen oxide emissions of the internal combustion engine 1 no longer being able to be converted due to the increased oxygen content. In order for the nitrogen oxide conversion of the catalytic converter device 30 to be reactivated, it is necessary to "clear" the catalytic converter device 30 again using a rich fuel-air mixture (combustion air ratio < 1).

[0019] Thus, short overrun cut-off processes of internal combustion engine 1 are neither optimal from a consumption nor emissions perspective due to the subsequent "catalytic converter clearing" with a rich fuel-air mixture. Depending on the gearshift, the combustion process within internal combustion engine 1 must therefore be reactivated before the gearshift, which also results in corresponding comfort disadvantages.

[0020] In the following, a method for operating the internal combustion engine 1 with overrun cut-off will be explained in more detail, by means of which the problems mentioned above can be remedied in a simple manner.

[0021] As in Fig.1, the automatic transmission 2 has a speed sensor means 20 on the input side, which is designed to detect the current speed of the internal combustion engine 1 at the input of the automatic transmission 2 and to continuously provide the associated measurement signal to the control device 4. The control device 4 is designed to determine a current speed gradient of the internal combustion engine 1 from the measured speeds and to estimate the duration of the next overrun cut-off process of the internal combustion engine 1 therefrom. The control device 4 is designed to prevent the overrun cut-off of the internal combustion engine 1 and thus also maintain the fuel supply if the estimated duration of the next overrun cut-off process of the internal combustion engine 1 falls below a specified or specifiable threshold value of a minimum overrun cut-off duration.This advantageously ensures that a minimum overrun cut-off duration of the internal combustion engine 1 is always guaranteed.

[0022] The method presented here is based on the realization that a minimum overrun cut-off duration of a few seconds is necessary to compensate for the subsequent increased fuel consumption for the necessary "catalytic converter clearing" in order to achieve an overall fuel consumption advantage. This minimum overrun cut-off duration can thus be used in the method to prevent overrun cut-off ("overrun cut-off prohibition") of internal combustion engine 1 for efficiency reasons.

[0023] This inhibition of the overrun cut-off (“overrun cut-off prohibition”) of the internal combustion engine 1, which is provided for reasons of efficiency, can be verified and set depending on various parameters.

[0024] It may, for example, be advantageous not to actively bring the internal combustion engine 1 out of a state of overrun cut-off and to reactivate the fuel supply, but to wait until a request signal from another system or consumer of the motor vehicle forces the internal combustion engine 1, which is made available to the control device 4, out of the state of overrun cut-off in order to make maximum use of the current overrun cut-off phase for reasons of efficiency.

[0025] As soon as fuel is supplied to the internal combustion engine 1 again after an overrun cut-off phase and the combustion process of the fuel-air mixture is reactivated, the overrun cut-off is preferably prevented by the control device 4 until a specified or specifiable minimum duration is reached again depending on the currently selected gear of the automatic transmission 2 and the speed of the internal combustion engine 1 (including hysteresis).

[0026] For operational strategy reasons, it may also be advantageous for no fuel to be supplied to the internal combustion engine 1 during overrun downshifts and for the combustion process of the fuel-air mixture within the internal combustion engine 1 to be deactivated. This operating strategy may or may not be advantageous, for example, depending on the strength of the current vehicle deceleration, so that the control device 4 preferably also checks whether the vehicle deceleration threshold has been exceeded. Furthermore, various other parameters, such as the current driving mode of the motor vehicle and / or the result of a check as to whether a previous event was identified as an overrun downshift, and / or the result of a check as to whether the overrun downshift occurred at most a defined time ago, can be incorporated into the operating strategy of the internal combustion engine 1, which is implemented by the control device 4.

Claims

[1] Method for operating an internal combustion engine (1) with overrun cut-off, in which a fuel supply to the internal combustion engine (1) is interrupted by a control device (4) of the internal combustion engine (1), wherein a current speed of the internal combustion engine (1) is detected at an input of an automatic transmission (2) and evaluated by the control device (4), wherein the control device (4) determines a current speed gradient of the internal combustion engine (1) from the detected speeds and estimates the duration of the next overrun cut-off process of the internal combustion engine (1) therefrom, wherein the control device (4) prevents the overrun cut-off of the internal combustion engine (1) and maintains the fuel supply to the internal combustion engine (1) if the estimated duration of the next overrun cut-off process of the internal combustion engine (1) falls below a specified or specifiable threshold value of a minimum overrun cut-off duration,and wherein the fuel supply to the internal combustion engine (1) is reactivated by the control device (4) after the end of an overrun cut-off process, wherein a renewed overrun cut-off is prevented by the control device (4) at least until a specified or specifiable minimum duration is reached again depending on the current gear of the automatic transmission (2) and the speed of the internal combustion engine (1). [2] Method according to claim 1, characterized by that the control device (4) maintains the overrun cut-off of the internal combustion engine (1) and interrupts the fuel supply until the control device (4) receives a request signal from another system or consumer of the motor vehicle to end the overrun cut-off of the internal combustion engine (1). [3] Method according to one of claims 1 or 2, characterized bythat the fuel supply to the internal combustion engine (1) is controlled by the control device (4) in such a way that no fuel is supplied during overrun downshifts and the combustion process of the fuel-air mixture within the internal combustion engine (1) is not activated.

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