The invention relates to a process for regenerating the exhaust-gas particle filter of an internal combustion engine with a supercharger unit having a preceding flap valve.
There are already statutory limits in some countries of the degree of particle emission from internal-combustion engines; other countries will follow suit, and it may generally be expected that the permissible limiting values of exhaust-gas particles will be made more stringent.
The particle emission from internal-combustion engines is composed essentially of the following constituents:
freely suspended soot,
hydrocarbon compounds and other organic substances added to the soot,
sulphate compounds,
lead compounds, particularly in spark-ignition engines.
It has not yet been possible hitherto to eliminate particle emission in internal-combustion engines completely by means of measures carried out within the combustion process, but progress has already been made in reducing particle emission as a result of precautions applied to the exhaust gases.
It is known from EP-A-No. 72,059 to arrange an exhaust-gas particle filter in the high-pressure part of the exhaust system in front of the pressure-wave machine. When clogging of the exhaust-gas particle filter occurs under partial load, the primary effect is that its pressure loss impedes the gas exchange of the engine, thus resulting in a reduction in useful power. The vehicle driver compensates for the power loss by supplying a greater quantity of fuel. If the vehicle driver demands sufficiently high power from the vehicle, the exhaust-gas temperature increases sharply and the exhaust-gas particles deposited in the filter burn off automatically. The temperature surge on which this control operation is based can also be achieved when the supercharging-air flap, exhaust-gas bypass valve or recirculation flap are briefly actuated. When the supercharging-air flap or recirculation flap is closed or the exhaust-gas bypass valve is opened, the supercharging-air density and consequently the excess air is briefly reduced, and with a constant fuel supply quantity this increases the exhaust-gas temperature.
However, this sporadic regeneration of the exhaust-gas particle filter necessarily results in continuously increasing clogging of the filter and therefore in a poor thermodynamic behaviour of the engine. Sporadic regeneration of the exhaust-gas particle filter means per se a random uncontrolled burn-off of the deposits and, because of the high temperature gradients and thermal stresses, leads to fatigue of the material and destruction of the filter. It must also be assumed that the resistance and high thermal inertia of the exhaust-gas particle filter worsen the fuel consumption and the driving performance, above all under transient conditions.