Method and device for increasing the temperature of an exhaust gas purification system

Abstract

Method for increasing the temperature of an exhaust gas purification system (16) in the exhaust gas duct (14) of an internal combustion engine during an operating phase with at least one deactivated cylinder (20), wherein an air-fuel mixture can be supplied to the internal combustion engine on the fresh air side, characterized in that, if a predetermined minimum temperature of the exhaust gas purification system (6) is undershot on the fresh air side, the air-fuel mixture is supplied, passed unburned through the at least one deactivated cylinder (20) and supplied to a reaction surface of the exhaust gas purification system (16), wherein the fuel-air mixture is supplied to the deactivated cylinder (20) in the form of fuel vapors from a crankcase ventilation (21).

Description

State of the art

[0001] The invention relates to a method for increasing the temperature of an exhaust gas purification system in the exhaust duct of an internal combustion engine during an operating phase with at least one cylinder switched off, wherein an air-fuel mixture can be supplied to the internal combustion engine on the fresh air side.

[0002] The invention further relates to a device for carrying out the method according to the invention.

[0003] The exhaust gas from internal combustion engines is cleaned of unwanted components by catalysts installed in the exhaust manifold. This process involves the conversion of substances such as nitrogen oxides, hydrocarbons, and carbon monoxide into carbon dioxide, oxygen, and water vapor on catalytically active surfaces. The intended effect requires that the exhaust gas composition falls within a suitable range. This is achieved by supplying the internal combustion engine with a stoichiometrically balanced fuel-air mixture. Furthermore, the catalytically active surfaces must reach a minimum temperature to ensure that the conversion processes can occur within the specified timeframe. This minimum temperature is reached by heating the catalysts with the temperature of the exhaust gas.In particular, during engine start-up, internal engine measures may be implemented to reduce the engine's efficiency, resulting in higher exhaust gas temperatures. This, however, increases fuel consumption. During engine operation, efficiency-enhancing methods such as deactivating individual cylinders or cylinder banks, or fuel cut-off during deceleration, may be employed. These measures can cause the minimum temperature of the catalytic converter, or parts thereof, to fall below the required level, thus reducing its cleaning effect. Therefore, in such cases, the engine is restarted, which, however, counteracts the efficiency gains.

[0004] To increase the temperature of the catalysts, one example of a solution is to inject fuel into the exhaust manifold of the internal combustion engine upstream of the catalyst. However, this requires additional components in the exhaust system, which increases the system price and complexity.

[0005] Furthermore, methods and devices exist for metering fuel on the fresh air side of the internal combustion engine, which aim to supply gases from the crankcase or fuel tank to the combustion process and control their contribution. German patent DE 102007054817A1 describes a method for warm-up control in an internal combustion engine with engine oil lubrication and a fuel supply, wherein the air-fuel ratio (lambda) of a fuel-air mixture supplied to the engine is determined by means of an exhaust gas probe in an exhaust gas channel of the engine. The method according to the invention provides that the heating of the engine oil during the warm-up phase of the internal combustion engine is monitored by means of an oil temperature control system and that, in the temperature range characteristic of a significantly high evaporation rate of the fuel from the engine oil, the heating is slowed down or interrupted.This reduces excessive fuel dilution resulting from a high rate of fuel evaporation from the engine oil during the warm-up phase, which has a beneficial effect on the control of the fuel-air mixture. Particularly in internal combustion engines operating on flex-fuel technology, this method can achieve more favorable emissions values ​​during the warm-up phase. However, this method does not increase the temperature of the exhaust gas and therefore not the catalytic converter.

[0006] German patent DE4421258A1 describes an internal combustion engine with at least two cylinder groups or cylinders, to which separate exhaust lines are assigned at least upstream of a catalytic exhaust gas purification device, and with a device for shutting down a cylinder group by interrupting the fuel supply while maintaining gas exchange through that cylinder group, wherein the gases expelled from the shut-down cylinder group are returned to the cylinder combustion chambers of a cylinder group. It is provided that the gases expelled from the shut-down cylinder group are introduced into the cylinder combustion chambers of the cylinder group that continues to be fired. The patent does not describe the supply of fuel vapors to unfired cylinders during a deceleration phase of the internal combustion engine.

[0007] German patent application DE102006009448A1 describes a multi-cylinder internal combustion engine with an exhaust system including an exhaust emission aftertreatment device for exhaust gases from the cylinders, an air supply system for supplying fresh air to the cylinders, a fuel supply system for supplying fuel to each cylinder, and a control unit for interrupting the fuel supply to one of the cylinders in order to shut that cylinder down. The multi-cylinder internal combustion engine has a valve assembly located between the cylinder and the emission aftertreatment device, which can be actuated to redirect gases from the cylinder back to the air supply system when the cylinder is shut down. German patent application DE102006009448A1 also does not describe the supply of fuel vapors to unfired cylinders during a deceleration phase of the internal combustion engine.

[0008] German patent DE 102007037541A1 describes a method for operating a motor vehicle's powertrain comprising at least one transmission and one drive unit, wherein, when the powertrain is operated in overrun mode, the drive unit can be switched to overrun fuel cut-off mode by a control device. The method provides that, during overrun fuel cut-off, the temperature of a powertrain catalyst is measured or determined analytically using a temperature model. Depending on the catalyst temperature, the control device switches the drive unit from overrun fuel cut-off mode to overrun fuel cut-off mode. Furthermore, an auxiliary consumer of the motor vehicle, which provides braking torque in the powertrain, is activated. If the catalyst temperature falls below a predetermined value, the engine is restarted.The generated torque is absorbed by the auxiliary consumer. The document does not describe the supply of fuel vapors to unfired cylinders during a coasting phase of the internal combustion engine.

[0009] DE 10 2011 085 281 A1 relates to a method for heating exhaust aftertreatment systems in motor vehicles with a spark-ignition internal combustion engine, wherein fuel is introduced into at least one combustion chamber at least during a coasting phase of the internal combustion engine, and appropriate measures are taken to ensure that the fuel-air mixture formed from the fuel and air flows into the exhaust aftertreatment system at least almost unignited. According to the invention, as a corresponding first measure, the fuel is injected into the combustion chamber only after ignition of the ignition component associated with that combustion chamber.

[0010] DE 199 63 929A1 discloses an internal combustion engine (1), in particular for a motor vehicle, which is equipped with several cylinders (3), a catalytic converter (12), and a control unit (18). The internal combustion engine (1) can be operated in overrun mode by the control unit (18). In overrun mode, fuel can be injected into at least one of the cylinders (3) by the control unit (18).

[0011] It is therefore an object of the invention to provide a method by which, if necessary, an increase in the temperature of catalysts provided in the exhaust duct of an internal combustion engine can be made possible.

[0012] It is also an object of the invention to provide a device for carrying out the method. Disclosure of the invention

[0013] The problem relating to the method of the invention is solved by supplying the air-fuel mixture to the exhaust gas purification system when a predetermined minimum temperature on the fresh air side is undershot. This mixture is then passed unburned through at least one deactivated cylinder and onto a reaction surface of the exhaust gas purification system. Through the deactivated cylinder, unburned fuel reaches the catalytically active reaction surface of the exhaust gas purification system, reacts exothermically there, and thus increases its temperature. This method allows the temperature of the exhaust gas purification system to be adjusted so that a sufficiently high temperature can be maintained, and its purification effect preserved, even during efficiency-enhancing measures such as cylinder deactivation.The fuel components on the fresh air side are drawn in by the deactivated cylinder, but are not burned due to the deactivated ignition or, in this case, the lean mixture. No additional equipment that would increase system costs or complexity is required. Premature re-firing of cylinders or cylinder banks to increase exhaust gas temperature and heat up the exhaust aftertreatment system can be avoided.

[0014] If the fuel-air mixture is supplied to the deactivated cylinder in the form of fuel vapors from a tank vent and / or crankcase vent, a fuel-containing mixture already present in the system can be used. The necessary supply lines are already in place, as they are already used for fired cylinders.

[0015] If the fuel-air mixture or fuel vapors are supplied to the fresh air side of the internal combustion engine via supply lines, and the amount of fuel supplied is adjusted by actuators located in the supply lines depending on the temperature of the exhaust aftertreatment system, the exhaust aftertreatment system can be kept within a suitable temperature range for cleaning, even during efficiency-enhancing measures. This method allows precisely the amount of fuel to be added to keep the operating temperature of the catalyst within the intended range, while preventing overheating and thus potential damage.

[0016] In a simple version of the control system, the supply of the air-fuel mixture or fuel vapors on the fresh air side and their passage through the deactivated cylinder are terminated when the temperature of the exhaust gas cleaning system reaches a predetermined upper value. Temperature control of the exhaust gas cleaning system is not provided here, but overheating and thus potential damage to it can be prevented.

[0017] In alternative embodiments, the temperature of the exhaust gas purification system is determined by means of a temperature sensor or by modeling. If the temperature sensor is omitted, its costs and the necessary supply lines can be eliminated.

[0018] The invention further relates to a device for increasing the temperature of an exhaust gas purification system in the exhaust duct of an internal combustion engine with a control system assigned to the internal combustion engine, wherein at least one cylinder of the internal combustion engine is designed to be switchable and wherein a supply for an air-fuel mixture or fuel vapors is provided on the fresh air side of the internal combustion engine.

[0019] The problem addressed by the device is solved by providing an actuator, controllable by the control unit, in the supply line on the fresh air side to adjust the flow rate, and by including a circuit or program sequence in the control unit to control the actuator and maintain a predetermined temperature range for the exhaust gas purification system. If the temperature of the exhaust gas purification system falls below the range suitable for purification, fuel can be added to the fresh air with the ignition switched off and fed unburned through the cylinder of the exhaust gas purification system. The fuel-containing mixture can be drawn from the crankcase or the tank vent and fed to the fresh air duct via existing lines. A valve, which can be activated by the control unit, serves as the shut-off device.

[0020] The device according to the invention is particularly suitable for an internal combustion engine with at least two cylinder banks and separate exhaust gas purification systems assigned to these cylinder banks. In such a V-engine, further actuation of the gas exchange valves (soft CDA; CDA = cylinder deactivation) results in particularly strong cooling of the part of the exhaust gas purification system connected to the deactivated cylinder bank, since all cylinders of that cylinder bank are deactivated. In this arrangement, drawing the air-fuel mixture from the tank vent is particularly suitable.

[0021] The invention is explained in more detail below with reference to an embodiment shown in the figure. It shows: Fig. 1. Schematic representation of an internal combustion engine with exhaust gas purification system.

[0022] Fig.Figure 1 shows a schematic representation of an internal combustion engine with one cylinder 20, to which fresh air is supplied via a fresh air inlet 11. Exhaust gases from the cylinder 20 are discharged via an exhaust gas channel 14 and passed through an exhaust gas purification system 16, in which unwanted components are catalytically converted. The internal combustion engine is associated with a control unit 10, which receives a temperature signal from a temperature sensor 15 that determines the temperature of the exhaust gas purification system 16. A fuel-air mixture in the cylinder 20 can be ignited by an ignition device 13, which is controlled by the control unit 10. A piston 22 is provided in the cylinder 20, which, during an ignition process, exerts a force on a crankshaft 23 and can thus drive a motor vehicle. The crankshaft 23 is surrounded by a crankcase 24 containing lubricating oil.During operation of cylinder 20, fuel is introduced into the lubricating oil at a lower temperature. At a higher temperature, this fuel is driven out of the lubricating oil and is present as fuel vapor in the crankcase 24. The fuel vapor can be fed to the fresh air supply 11 via a crankcase ventilation vent 21. According to the prior art, the fuel vapor is used to enrich the air-fuel mixture supplied to the internal combustion engine and is combusted in cylinder 20.

[0023] According to the invention, fuel vaporization is metered into the fresh air supply 11 by an actuating element 12 when the control unit 10 detects via the temperature sensor 15 that the exhaust gas purification system 16 falls below a predetermined lower temperature and the internal combustion engine is in an operating state in which the ignition device 13 is switched off, but the engine as a whole is running and other cylinders (not shown here) are in operation, or the engine is in overrun mode. Since the ignition device 13 is switched off, the unburned fuel vaporization passes through the cylinder 20 into the exhaust gas purification system 16 and reacts exothermically on the catalytic surfaces there. According to the invention, this raises the temperature of the exhaust gas purification system 16 to a range in which it can effectively exert its purification effect.The actuator 12 can be controlled by the control unit 10 so that the temperature of the exhaust gas purification system 16 is regulated within a suitable operating range, taking into account the operating parameters of the internal combustion engine.

[0024] In an alternative embodiment, the fuel vapor can also be taken from a tank vent and metered into the fresh air supply 11 via an actuator provided there, the actuator being appropriately controlled by the control unit 20. Furthermore, it can be provided that the temperature sensor 15 is omitted and the temperature of the exhaust gas purification system 16 is modeled in the control unit 10 based on the operating parameters of the internal combustion engine.

Claims

[1] Method for increasing the temperature of an exhaust gas purification system (16) in the exhaust duct (14) of an internal combustion engine during an operating phase with at least one cylinder (20) deactivated, wherein an air-fuel mixture can be supplied to the internal combustion engine on the fresh air side, characterized by that when a predetermined minimum temperature of the exhaust gas purification system (6) on the fresh air side is undershot, the air-fuel mixture is supplied, passed unburned through the at least one deactivated cylinder (20) and supplied to a reaction surface of the exhaust gas purification system (16), wherein the fuel-air mixture is supplied to the deactivated cylinder (20) in the form of fuel outgassing from a crankcase ventilation (21). [2] Method according to claim 1, characterized bythat the fuel-air mixture or the fuel outgassing is supplied to the fresh air side of the internal combustion engine via supply lines and that the supplied fuel quantity is adjusted by adjusting elements (12) arranged in the supply lines as a function of the temperature of the exhaust gas purification system (16). [3] Method according to one of claims 1 to 2, characterized by that the supply of the air-fuel mixture or the fuel outgassing on the fresh air side and the passage through the deactivated cylinder (20) is terminated when the temperature of the exhaust gas purification system (16) reaches a predetermined upper value. [4] Method according to one of claims 1 to 3, characterized by that the temperature of the exhaust gas purification system (16) is determined by means of a temperature sensor (15) or by modeling. [5] Device for increasing the temperature of an exhaust gas purification system (16) in the exhaust duct of an internal combustion engine with a control (10) assigned to the internal combustion engine, wherein at least one cylinder (20) of the internal combustion engine is designed to be switchable off and wherein a supply for an air-fuel mixture or fuel outgassing is provided on the fresh air side of the internal combustion engine, characterized by that an actuating element (12) which can be actuated by the control system (10) is provided in the supply line on the fresh air side for adjusting the flow, and that a circuit or program sequence is provided in the control system for actuating the actuating element (12) in order to maintain a predetermined temperature range of the exhaust gas purification system (16), wherein the internal combustion engine is designed with at least two cylinder banks and with separate exhaust gas purification systems (16) assigned to these cylinder banks.

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