DE4434835A1 - Exhaust system - Google Patents

Abstract

The invention relates to an exhaust system for an internal combustion engine (1) with at least one exhaust emission control unit (main catalytic converter 8, adsorption device 10, secondary catalytic converter 11) arranged in an exhaust line (3) and a device for the supply of secondary air, which has a valve device which can be influenced by a control module. In order to prevent increased pollution immediately after starting of the internal combustion engine (1), a method of operation is proposed according to which the supply of secondary air is automatically maintained for a predefinable period of time even after shutting-off of the internal combustion engine (1). <IMAGE>

Description

The invention relates to an exhaust system according to the preamble of Claim 1.

A generic exhaust system has become known from the DE-41 27 596-A1 (F01N 3/10). It describes in detail as in particular when cold starting an internal combustion engine Emission of pollutants in the exhaust gas can be reduced effectively can. One is of particular importance in this context Device for supplying secondary air. With this it is possible Lich, with a catalytically effective converter in the start-up phase To operate excess oxygen. It has an oxidizing effect means the chemical reaction is exothermic, making its own Heating and the heating of the exhaust gases leaving it be accelerated.

An exhaust system is also to be regarded as generic according to US-PS-37 91 143 (F01N 3/14). This also shows exhaust gas cleaning ger, to which secondary air can be supplied. However, too an additional injection of fuel into the exhaust gas system, especially in the start-up phase, heating of the pre-catalytic converter, which is preferably arranged close to the machine to effect tors.

To round off the prior art, reference is still made to DE-AS-14 51 881 (F01N 3/10). This also reveals one Exhaust gas line consisting of pre-catalytic converter and main catalytic converter supply device. Details on the way of air supply however, this document cannot be found.

The invention has for its object generic exhaust gas systems with reduced equipment expenditure with regard to their To further improve the cleaning effect.

This problem is solved by the characteristic features of the Claim 1. The sub-claims contain appropriate Wei further developments of the invention.

According to the invention, a three-way catalytic converter is used as an exhaust gas purifier and an adsorption device of the internal combustion engine in series downstream. Each upstream of these exhaust gas purifiers open into the exhaust gas instructions supply lines for the secondary air. These are separately switchable, so that individually at each Ab specified air volumes can be set by gas cleaners. With which he The combination proposed according to the invention is in the starting phase as usual the engine with a relatively rich mixture with low operated against nitrogen oxide emissions. With simultaneous supply secondary air becomes a combustion of the rich starting mixture and also rapid heating of the three-way catalyst reached. The resulting in this "rich" mode of operation Increases in hydrocarbon and carbon monoxide levels are adsorbed in the still cool adsorption device. On this way the total amount of different pollutant components are noticeably reduced, especially in the start-up phase.

In addition or as an alternative to the solution according to patent claim 1 can also significantly reduce pollutant emissions be when the exhaust system according to the pre-defined in claim 5 operating mode works. By the invention Proposed supply of secondary air for a predetermined time span even after the internal combustion engine is switched off Flushing the exhaust pipe with fresh air. Consequently no residual exhaust gases can remain in the exhaust system. These Measure is based on the inventive consideration that esp especially in the case of internal combustion operated with alcohol fuels Remaining exhaust gases remain in the exhaust line, from which the  Water vapor contained in the exhaust gas at the gradually cooling Walls condensed. When restarting the burner the condensed water acts in the adsorber device as adsorbate and thereby reduces the absorption capacity of the Adsorbers for hydrocarbons on restart. That nega The flushing according to the invention is very effective effectively. This also makes the adsorber unit cooled down and restarted the engine made ready so that e.g. B. the hot start of an engine HC emissions from the so-called start cloud are adsorbed.

The implementation of the solutions according to the invention only requires minor program changes to already existing ones Control units. With the operation according to claim 5 can can be easily converted with exhaust systems in series. In addition, the purging with fresh air is also independent depending on the design of the exhaust system.

A preferred application of the invention is an exhaust gas location, in the exhaust pipe at least two in a row arranged exhaust gas cleaners can flow through the entire exhaust gas flow are. In this case, both the whole and a part of the exhaust system are flushed with fresh air if in flow direction before the first and second exhaust gas purifiers open a valve control influenceable supply lines.

Further reductions in pollutant emissions can be achieved if, for example, the adsorption device is still a Auxiliary catalyst is connected downstream, the volume of construction is lower than that of the main catalyst. In a preferred one Embodiment has the adsorption device as an adsorber a zeolite and the auxiliary catalyst a coating Palladium on. The latter is less expensive than the previous one used platinum-rhodium coatings and enables a Conversion of hydrocarbons and carbon monoxide already from approx. 200 ° C.

A particularly advantageous embodiment of the invention is shown in the drawing. An internal combustion engine 1 with an intake line 2 and an exhaust gas line 3 can be seen in a side view. Essential elements of the intake line 2 are an air flow meter 4 , a throttle valve 5 and an injection valve 6 . The most important components of the exhaust line 3 include a λ probe 7 , a main catalytic converter 8 designed as a three-way catalytic converter, a front silencer 9 , an adsorber device 10 and an auxiliary catalytic converter 11 . The latter two components are housed in a common housing 12 , to which a temperature sensor 13 and a second λ probe 14 are additionally attached. The temperature of the adsorber device 10 or of the auxiliary catalytic converter 11 can be detected via this temperature sensor 13 , for example. Another temperature sensor 15 is assigned to the main catalytic converter 8 . Depending on the signals supplied by these, for example, a changeover valve 18 can be controlled.

A secondary air pump 16 , from which a shut-off valve 17 and the switching valve 18 are arranged downstream, is particularly important for the application of secondary air to the exhaust line 3 . The air mass flow supplied by the secondary air pump 16 can be distributed by this changeover valve 18 via a first feed line 19 and / or a second feed line 20, depending on the specification of a control device 21 , which is only shown symbolically here. The control device 21 is not only connected to the sensors or sensors shown in the drawing, but also evaluates, for example, the speed n _{Mot of} the internal combustion engine 1 , the air temperature T _air in the intake line 2 and the temperature T _{cooling of} the cooling water in the Internal combustion engine 1 . The idle speed n _{empty of} the internal combustion engine is also monitored. Without being influenced by the Steuerein device 21 is a check valve 22 arranged in the first supply line 19 , which prevents the backflow of exhaust gas into the secondary air supply system. Basically, an arrangement of the check valve 22 in the supply line 20 is conceivable.

Of particular importance in connection with the invention is a timer 23 , which is connected downstream of an ignition switch 24 . As soon as the internal combustion engine 1 is switched off via the ignition switch 24 , the timing element 23 ensures that the operation of the secondary air pump 16 is switched on for a predefinable period of time. If the internal combustion engine 1 at the time of shutdown, the secondary air pump 16 will not have been in operation is also carried out in dependence on the signals of the timing element 23, a Power On processing the secondary air pump sixteenth This wake is particularly important when using alcohol fuels because they cause particularly heavy rainfall of water in the exhaust system.

For the construction shown in the drawing, an operating mode is advantageous, at least in the warm-up phase, in which the internal combustion engine 1 is operated as usual with a rich starting mixture (λ ≃ 0.7-0.9). In front of the main catalytic converter 8 , the system is supplied with secondary air via the supply line 19 . This measure causes combustion of the fat mixture and thus accelerated heating of the main catalyst 8 . This causes a significant reduction in the nitrogen oxide content. The increased output of hydrocarbons and carbon monoxide during the start-up and warm-up phase can be made harmless by the adsorption device 10 . According to the invention, when the operating heat in the main catalytic converter 8 and the adsorption device 10 has been reached, the operation of the internal combustion engine 1 should now take place in such a way that the λ probe 7 controls λ = 1.0, but within the so-called λ window on the "rich" Side ", for example with λ = 0.98. As a result, carbon monoxide and hydrocarbon emissions increase slightly; however, nitrogen oxide emissions decrease.

The increasing emissions of hydrocarbons and carbon monoxides are made harmless in the downstream auxiliary catalytic converter 11 by oxidizing it - e.g. B. with λ = 1.1 to 1.2 - operated. At the same time, the secondary air is controlled or regulated by the supply line 20 downstream of the main catalytic converter 8 and upstream of the auxiliary catalytic converter 11 as a function of signals from appropriately designed sensors (eg λ-probe 14 ).

Through this different operation of the main catalyst 8 (low fat) and auxiliary catalyst 11 (lean), the pollutants can be converted even more effectively overall. For normal driving conditions, the secondary air pump 16 is then in continuous operation. After completion of the warm-up phase, an interruption of the secondary air supply to the main catalytic converter 8 is necessary, because the catalytic converter 8 is then sufficiently warm and operates selectively.

In order to also keep the auxiliary catalytic converter 11 at the required temperature level in all operating states, it can also be heated in a further embodiment variant electrically or by a different type of energy supply, depending on the temperature.

With the configuration shown in the drawing, the supply of secondary air can be optimally controlled depending on the operating state of the internal combustion engine 1 . For example, when the engine is cold, the supply line 19 is first opened, so that an exothermic reaction of hydrocarbons with oxygen from the air takes place in the exhaust pipe. The main catalyst 8 is heated up faster and reaches its jump temperature after a short time. The mixture, which is usually displayed in bold on cold start, can thus be largely converted. After completion of the warm-up phase, the supply line 19 to the main catalyst 8 is blocked so that it can work selectively. Switching the air supply to the supply line 20 ensures a good residual conversion of remaining pollutants in the auxiliary catalytic converter 12 . Investigations by the inventors have shown that operation in the range λ = 1.1 to 1.2 is particularly advantageous for the residual conversion. This type of lean operation is regulated via secondary air from the supply line 20 . A second λ probe ( 13 or 14 ) may be required to control this operation.

The invention is not based on that shown in the drawing Embodiment limited, but can also with others Exhaust systems with secondary air supply can be used as desired. For example, there is also a direct start catalyze sator directly on the engine in the arrangement according to the invention integrable.

Claims (6)

1. Exhaust system for an internal combustion engine ( 1 ) with

• - An exhaust gas cleaning system arranged in an exhaust pipe (main catalytic converter 8 , adsorption device 10 ),
• a pump device (secondary air pump 16 ) for the supply of secondary air,
• a valve device controlling the supply of the secondary air at various points in the exhaust pipe (changeover valve 18),
• - a control device ( 21 ) influencing the valve device,

characterized in that

• - The internal combustion engine ( 1 ) as an exhaust gas purifier for the total th exhaust gas mass flow as a three-way catalyst main catalyst ( 8 ) and an adsorption device ( 10 ) are connected in series,
• - By the valve device (changeover valve 18 ) optionally via one or more supply lines ( 19 , 20 ) of the main catalyst ( 8 ) and the adsorption device ( 10 ) separately or jointly with secondary air.

2. Exhaust system according to claim 1, characterized in that the adsorption device ( 10 ) has an auxiliary catalyst ( 11 ) is switched on, the construction volume of which is smaller than that of the main catalyst ( 8 ). 3. Exhaust system according to claim 1 or 2, characterized by an operating mode according to which the main catalytic converter ( 8 ) is operated predominantly in the rich range within a control window oriented at the value λ = 1. 4. Exhaust system according to claim 3, characterized by a mode of operation, according to which the adsorption device ( 10 ) and / or the auxiliary catalyst ( 11 ) are operated within a control window designed for lean operation. 5. Exhaust system for an internal combustion engine

• an exhaust gas purification system arranged in an exhaust pipe,
• a pump device (secondary air pump 16 ) for the supply of secondary air,
• a valve device controlling the supply of the secondary air at various points in the exhaust pipe (changeover valve 18 ),
• - One of the valve device (changeover valve 18 ) influencing control unit ( 21 ), in particular according to claim 1, characterized by an operating mode according to which the supply of secondary air for a predetermined period after switching off the internal combustion engine ( 1 ) is automatically switched on or maintained.