Method for operating an externally ignited internal combustion engine

Abstract

A method for operating a spark-ignition internal combustion engine in a motor vehicle with an intake-side and / or exhaust-side variable-stroke valve train for at least one gas exchange valve for a charge exchange and with at least one combustion chamber in which combustion of a fuel / air mixture is possible and with an exhaust system arranged on the combustion chamber for the discharge of combustion exhaust gas, wherein a particulate filter is arranged in the exhaust system when a particle load and / or a temperature of the particulate filter exceeds a threshold value and the motor vehicle is in a deceleration phase, characterized by the following method steps: - Reducing a gas exchange valve stroke, - Switching off the fuel supply to the combustion chamber.

Description

[0001] The invention relates to a method for operating an externally ignited internal combustion engine with the features from the preamble of claim 1.

[0002] For the technical context, reference is made, for example, to German Patent Application DE 10 2014 208 915 A1. This application discloses a method for operating a motor vehicle's internal combustion engine in overrun mode with low emissions and low fuel consumption. The internal combustion engine has an injection system and an exhaust system with a catalyst. At least one lambda sensor is installed in the exhaust system, which controls the air / fuel mixture to achieve a desired result. During overrun, a signal from the at least one lambda sensor is evaluated.

[0003] German Patent Application DE 10 2004 019 831 A1 discloses a further method for operating an internal combustion engine of a motor vehicle. The internal combustion engine has an exhaust system with an exhaust catalyst, as well as a gas exchange device with an intake side and an exhaust side, which is controlled by a control unit according to a predetermined operating mode for a charge exchange with an intake stroke and an exhaust stroke. It is proposed that during a deceleration phase, as a non-fired operating mode of the internal combustion engine, a targeted metering of fuel is carried out in such a way that a catalyst mass flow with a defined, predetermined lambda value is supplied to the catalyst device to prevent undesirable oxygen exposure of the exhaust catalyst.

[0004] Furthermore, a device for controlling an internal combustion engine is known from German patent application DE 10 2015 220 876 A1. The engine comprises at least one cylinder with an inlet valve and an exhaust valve, and at least one catalyst for exhaust aftertreatment is connected downstream. The device includes a control unit. To improve the warm-up behavior of a catalyst in the exhaust system of an internal combustion engine, it is proposed that the control unit be configured to - to detect an under-temperature of the catalyst and - to close and keep closed at least one valve of each cylinder when there is simultaneous under-temperature control and overrun switching.

[0005] This proposed control system improves the warm-up behavior of a catalyst, such as a 3-way catalyst, during overrun switching in the exhaust system of an internal combustion engine.

[0006] The increasingly stringent emission standards for internal combustion engines are driving significant development efforts in this area. The automotive industry is constantly and systematically searching for ways to optimize exhaust aftertreatment and implementing the solutions found in series production. During this ongoing optimization process, in addition to the usual steady-state operating conditions of the internal combustion engine, critical transition phases are increasingly coming into focus. These include situations such as a cold start or start-stop phases at traffic lights. A particularly critical transition phase also occurs during deceleration, when the driver releases the accelerator and allows the vehicle to coast. To conserve fuel, no fuel is injected into the cylinders of the internal combustion engine during deceleration.The intake and exhaust valves continue to open and close, thus pumping a large amount of fresh air, and therefore oxygen, through the exhaust system and consequently through the gasoline particulate filter (GPF). A gasoline particulate filter is a particulate filter for a spark-ignition internal combustion engine. As a result, the GPF's effectiveness is negatively affected by the excess oxygen. If a temperature of 500°C is exceeded and sufficient oxygen is present, the accumulated soot particles in the GPF are burned off. A certain amount of soot buildup is actually desirable, as a new, unused GPF has a filtration rate of only 70%. With the right amount of soot deposits, the filtration rate increases to over 95%, thus significantly exceeding the required rate.Therefore, if one switches to acceleration while the temperature in the gasoline particulate filter is 500°C or higher, unwanted soot combustion can occur.

[0007] There are already approaches to solving this problem; one approach involves activating fuel injection and thus combustion during deceleration, so that the unintentionally injected oxygen is burned before it enters the exhaust system. However, this measure has a negative impact on CO2 emissions, meaning fuel consumption increases, and also affects the vehicle's handling.

[0008] The object of the present invention is to demonstrate a measure to reliably prevent unwanted soot combustion in a gasoline particulate filter.

[0009] This problem is solved by the process steps in the characterizing part of claim 1.

[0010] A further development of the invention is described in the single dependent claim.

[0011] The idea according to the invention is to significantly reduce the stroke of all intake and / or exhaust valves during overrun fuel cut-off, possibly even to zero (zero stroke), so that little or, in the case of zero stroke, no oxygen enters the gasoline particulate filter, which would otherwise burn up due to the temperature and the soot load. The deactivation of the gas exchange valves, on the intake and / or exhaust side, can be achieved, for example, via a variable-stroke valve train. Another possibility is, for example, to use switching cams or switching tappets in the valve train.

[0012] The extent to which the gasoline particulate filter is in the described condition (loading level and temperature above 500 °C) can be determined, for example, using a loading and / or temperature model in a control unit. Another method involves measuring these parameters, for example, with pressure and temperature sensors.

[0013] With the strategy according to the invention, it is also possible to shut off the fuel supply during a coasting phase of a motor vehicle and, by means of the reduced gas exchange valve stroke or, if applicable, by a set zero stroke, to prevent oxygen from being pumped through the gasoline particulate filter. This significantly reduces all the aforementioned disadvantages, or, in the case of a zero stroke, eliminates them completely.

[0014] The inventive method for operating a spark-ignition internal combustion engine offers the following advantages: - minimized risk or complete prevention of unwanted soot combustion in the gasoline particulate filter, - Minimizing fluctuating NO x -Emissions through overrun fuel cut-off, - no increased CO2 emissions or fuel consumption, - no undesirable driving behavior of the vehicle.

[0015] A method for operating a spark-ignition internal combustion engine in a motor vehicle with an intake-side and / or exhaust-side variable-lift valve train is thus proposed, for at least one gas exchange valve for a charge exchange in at least one combustion chamber in which combustion of a fuel / air mixture is possible, and with an exhaust system arranged on the combustion chamber for the discharge of combustion exhaust gas, wherein a particulate filter is arranged in the exhaust system when an ash load and / or a temperature of the particulate filter exceeds a threshold value and the motor vehicle is in a deceleration phase, comprising the following process steps: - Reducing a gas exchange valve stroke, - Switching off the fuel supply to the combustion chamber.

[0016] It is particularly preferred that the gas exchange valve stroke be set to zero stroke.

Claims

[1] Method for operating a spark-ignition internal combustion engine in a motor vehicle with an intake-side and / or exhaust-side variable-stroke valve train for at least one gas exchange valve for a charge exchange and with at least one combustion chamber in which combustion of a fuel / air mixture can be carried out and with an exhaust system arranged on the combustion chamber for the discharge of exhaust gas from the combustion, wherein a particulate filter is arranged in the exhaust system when a particulate load and / or a temperature of the particulate filter each exceeds a threshold value and the motor vehicle is in a deceleration phase, characterized by the following procedural steps: - Reducing a gas exchange valve stroke, - Switching off the fuel supply to the combustion chamber. [2] Method according to claim 1, characterized by the following method step: - Reduction of the gas exchange valve stroke to zero stroke.