The invention relates to a control method for increasing the exhaust gas temperature of an internal combustion engine, which has at least one exhaust gas aftertreatment device in its exhaust tract, and which has an exhaust gas recirculation system, to which a regulating system is assigned.
EP 0 521 411 A1 discloses an exhaust gas pipe of an internal combustion engine, having at least one catalytic converter arranged in the exhaust pipe, and an adjustable throttle element arranged in said pipe. The throttle element is arranged with a fixed upstream end adjacent to a side wall of the exhaust pipe. A moveable downstream end is arranged so as to form a gap between it and an opposing side wall when the internal combustion engine is cold.
U.S. Pat. No. 7,131,271 B2 is concerned with a method for controlling a low-pressure exhaust gas recirculation of an internal combustion engine. The exhaust gas recirculation system has a throttle valve and an exhaust gas recirculation valve. Control of the two valves is coordinated by a central control unit, so that the respective valve is adjusted selectively. If the throttle valve is closed, the exhaust gas recirculation valve is simultaneously opened due to the pressure build-up.
Internal combustion engines usually have exhaust gas aftertreatment devices, such as catalytic converters and particle filter, such as a diesel particle filter, in their exhaust tract. These exhaust gas aftertreatment devices are known to need a certain exhaust gas temperature level in order to reduce CO in the exhaust gas, for example, or in the case of the diesel particle filter in order to be able to perform a required regeneration. For example, the exhaust gas temperature can be increased by means of a post-injection of fuel into the combustion chamber. This post-injection is performed after a timed main injection, usually fixed briefly before or after the top dead center of the piston. One problem of post-injection is that a proportion of the additional fuel injected is not burned, but is precipitated on the inside walls of the cylinder and can get into the engine oil. The disadvantage of an unwanted dilution of the engine oil with fuel thereby has to be accepted in order to obtain the advantage of an increase in the exhaust gas temperature.
Conventional intake and exhaust systems of an internal combustion engine require extensive control and calibration, in order to ensure an acceptable performance both during dynamic operation of the engine and in stationary operation. A major problem, especially in the case of diesel engines, is the extremely difficult coupling between the exhaust gas recirculation control and the separate boost pressure control. This means that it is currently not possible to regulate one of the two parameters without upsetting or having a detrimental effect on the adjustment of the other parameter. Instead both parameters have to be monitored and/or adjusted in parallel. This requires separate control elements for each of them, which have to be adjusted separately and which are extremely cost-intensive.
This invention is directed to providing a control method for increasing the exhaust gas temperature, in which dilution of the engine oil can be largely avoided.
According to the invention, the regulating system increases the exhaust gas back-pressure, whilst maintaining an exhaust gas recirculation rate, and a fuel injection quantity into the combustion chamber is here increased during the main injection, and/or the main injection is deferred to a later time.
In another embodiment of the present invention, the system increases the fuel injection quantity, followed by deferring the main injection if the required exhaust gas temperature or the required exhaust gas temperature level is not achieved via increased fuel injection. In an alternative embodiment, it is beneficial to defer the main injection to a later time, without increasing the exhaust gas back-pressure. In yet another embodiment of the present invention, it is also beneficial to defer the main injection to a later time, followed by possible increases in the exhaust gas back-pressure and the fuel injection quantity.