DE4322736A1 - Vehicle exhaust system with catalyser - has gas by=pass switched in when engine is in idle or cuts out - Google Patents

Abstract

A vehicle exhaust system is fitted with a catalyser and a bypass system such that the catalyser can be switched in and out. Upon engine (1) cut out, the gas flow path is switched to the bypass (8) position, and at idle speeds the gas also flows the bypass route. As soon as the engine cuts out, the flaps (7) are moved to their other position by a control device having sensors for the throttle flap or the accelerator position and r.p.m. of the engine. ADVANTAGE - Avoids unwanted sudden cooling of catalyser.

Description

The invention relates to an exhaust system according to the preamble of Claim 1. Such exhaust systems with a bypass for Directing the exhaust gas flow around the catalyst assembly to solve three tasks:

Catalysts need a certain min minimum temperature, but on the other hand are against excessive temperature vulnerable. For this reason it is known to protect a catalyst arrangement against excessive temperatures Exhaust gases flow through the bypass around the catalyst to redirect. To achieve an early start of the Catalytic converter arrangement during warm-up of an internal combustion engine, i. H. after a cold start, find catalyst assemblies with a close to the machine (and therefore quickly heating up) Starting catalyst and a ma away from the machine (so that it does not assume too high temperatures can) main catalyst application. During warm-up, i.e. H. if the exhaust gases are still cold, the bypass to the catalytic converter is ge locks, so that the entire exhaust gas flow through the start catalytic converter sator is conducted while after warming up, d. H. in the presence of hot exhaust gases and after heating the main kata lysators, the exhaust gas flow bypassing the starting catalyst is passed through the bypass. Finally, there are suggestions ge, when using leaded fuel for avoidance a "poisoning" of the catalyst material, the exhaust gases around the To redirect catalyst assembly.  

However, the fact that in the operation of an internal combustion engine driving a vehicle machine with modern engine management operating phases occur, in which - generally speaking - the exhaust system from cold Is flowing through gases. This is always the case when high Excess air is worked, especially in overrun mode with overrun cutoff, d. H. Switch off the fuel supply in the operating phases in which the internal combustion engine as driving brake acts. Similar conditions can be idle operation. So the catalyst assembly during such operating phases from the gas flow in the exhaust system flows through, the catalyst arrangement can be undesirable Cooled way, so that for example after completion of the push operation, i.e. after the transition from the push to the train drove the catalytically active material for a certain time does not have the temperature required for conversion.

The invention is therefore based on the object, a genus to create a proper exhaust system that such "conversion gaps "during the operation of the vehicle internal combustion engine avoids.

The inventive solution to this problem consists in the characterizing features of the main claim, an advantageous Further development of the invention describes the subclaim.

Such a control is essential for the invention the one formed, for example, by a flap or a valve Means for switching the exhaust gas flow between catalyst order and bypass that during overrun fuel cutoff phases which are the combustion chambers of the machine and accordingly the exhaust gas system is essentially permeated by relatively cold air, the catalyst arrangement outside the flow path thereof lies, so that cooling by convection is avoided.

An embodiment of the invention is explained below with reference to the drawing. At 1 , the usual and therefore not to be described structure possessing a vehicle driving internal combustion engine is indicated. The exhaust manifold 2 is used to collect the exhaust gases of all combustion chambers (cylinders) of the engine 1 and passes them into the exhaust pipe 3 , in which the catalyst arrangement 4 known and therefore not to be described structure and in series with this the silencer 5 and the rear silencer 6 are.

In the direction of flow in front of the catalytic converter arrangement 4 , the flap 7 can be seen, which, in the position shown, guides the exhaust gas flow leaving the engine 1 around the catalytic converter arrangement 4 through the bypass 8 . In the drawing, it is assumed that the internal combustion engine 1 in overrun with overrun cutoff, that is to say the cutoff of the fuel supply, is working, so that the combustion chambers of the machine 1 are essentially flowed through by cold air, which flows through the catalyst arrangement 4 when it flows through them in an undesirable manner would cool down.

On the other hand, as soon as the overrun mode or the overrun cutoff is lifted, the flap 7 is pivoted into its other position indicated at 7 'in a position in which it now switches off the bypass via a control unit with sensors for throttle or accelerator pedal position and engine speed 8 releases the catalytic converter arrangement 4 for flow through with the now again hot exhaust gas.

With the invention is accordingly a gat with simple means Exhaust system in accordance with the created during operation the internal combustion engine otherwise through operating phases of the same conditional cooling of the catalyst arrangement is avoided.

Claims (2)

1. Exhaust system for an internal combustion engine serving as a vehicle drive with a catalytic converter arrangement, a bypass to this as well as means for switching the exhaust gas flow between the catalytic converter arrangement and bypass, characterized in that the means ( 7 ) the exhaust gas flow during overrun cutoff operation of the machine ( 1 ) switch to the bypass ( 8 ). 2. Exhaust system according to claim 1, characterized in that the means ( 7 ) switch the exhaust gas flow when idling the machine ne ( 1 ) on the bypass ( 8 ).