GB2088476A

GB2088476A - An internal engine combustion engine exhaust system

Info

Publication number: GB2088476A
Application number: GB8134585A
Authority: GB
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1980-11-29
Filing date: 1981-11-17
Publication date: 1982-06-09
Also published as: FR2495220A1; FR2495220B1; DE3045112A1; SE452351B; DE3045112C2; IT1139831B; IT8125251A0; GB2088476B; SE8107098L

Abstract

An exhaust pipe 1 of an internal combustion engine is connected by branch duct 4 to a filter (2) dowstream of which is exhaust gas sensor 3, the discharge which is either returned to the engine through intake duct 10 or returned to the main exhaust stream. Sensor 3 has heating means 9 contained in common housing 8 and the condensate outlet of the filter may include throttle 7 to obtain the required flow characteristic for sensor 3. Pump 12 may be provided to assist the flow of exhaust gas and pressure peak responsive valves (13, 14, 15) may be provided to control the flow of exhaust gases from and into the main exhaust stream. <IMAGE>

Description

SPECIFICATION An internal combustion engine exhaust system This invention relates to an internal combustion engine exhaust system, having a sensor which monitors the composition of the exhaust gases.

As is known, senors which are suitable for detecting of analysing exhaust gases are used in the main exhaust gas stream of the exhaust system. As a result of this, the sensor is subjected to very high and predominantly thermal stresses.

The present invention seeks to provide an exhaust system which protects the sensor from damage and consequently from premature ageing caused by contamination, thermal stress, overstress and mechanical stress.

According to the invention there is provided an exhaust system of an internal combustion engine having a filter and a sensor which detects the composition of the exhaust gases, wherein the sensor is located in a by pass system of the exhaust system.

In a preferred embodiment of the invention its sensor is provided in a separate sensor housing having a heating means and spaced from the filter. The stream of exhaust gas bled off from the main exhaust stream may be returned after filtering and sensing either back to the main exhaust stream or to an inlet duct connected to the internal combustion engine.

Athrottle may be provided, in another embodiment of the invention downstream of the filter and a pump may be provided to the discharge duct downstream of the sensor. In another embodiment of the invention, pressure-peak responsive valves are provided between the main exhaust pipe and the partial streams of exhaust gas taken from and returned to the main exhaust pipe.

The measures proposed enable the sensor to be heated independently of the exhaust gas temperature. Consequently, the sensor can be operated within its own optimum temperature range as a result of a predetermined heating capacity or output.

Embodiments ofthe invention will now be described in more detail below by way of example and with reference to the accompanying drawings, in which Figure 1 illustrates automatically one arrangement of an internal combustion engine to hand system provided with a filter and a sensor. Figure 2to 6 illustrate respectively different embodiments ofthe exhaust system. In each embodiment, parts having the same function have the same reference numerals.

The bypass system shown in Figs. 1 to 6 consists of an exhaust gas feed pipe 4, which branches from an exhaust pipe 1 of an internal combustion engine (not shown) and leads through a filter 2 to a sensor 3, a discharge pipe 6 which is provided for the disposal of or discharge of filtered-off substances, for example water, and in the embodiments of Figures 1 to 4 and 6, a throttle 7 which is inserted in the discharge pipe 6.

The sensor 3 is fitted in a heatable sensor housing 8 which is constructed in such a way that heating elements 9 in the sensor housing 8 transmit heat mainly to the sensor 3 in order that the latter may operate within a temperature range which is favourable for the monitoring of exhaust gases. The heating capacity in this connection is designed accordingly. The heating elements, which are of a ceramic or even metallic type, are mounted so as to enable simple replacement of the sensor 3 without impairing the function of the heating elements 9.

The previously known modular unit consisting of the filter 2 and sensor 3 is not used and the spatial separation of the filter 2 from the sensor 3 has the advantage that filtering efficacy is considerably higher as a result of lower temperatures in the filter 2.

The exhaust gas which is taken from the exhaust pipe 1 is conducted through the filter 2 to the sensor 3 and passes from there to the intake pipe 10 shown in Fig. 1. The filtered-off substances, together with any collected water are also conducted to the intake pipe 10 by way of the discharge pipe 6 and the interposed throttle 7. However, this can also be effected in such a way that the exhaust gas pipe 5 and the discharge pipe 6 lead into a collecting return line 11 which is connected to the intake pipe 10 as shown in Fig. 2. However, the collecting return line 11 can also be connected directly back to the exhaust pipe 1 as shown in Figs. 4 and 6. The function of the interposed throttle 7 is to ensure a sufficient partial stream of exhaust gases through the sensor 3.

The exhaust gas return line to the intake pipe has the advantage that, depending on the quantity of the partial stream of exhaust gases recycled, a reduction in the pollutants of the combustion or exhaust gas can be achieved.

In addition and as shown in Figs. 3 and 4 a pump 12 can be used to improve the delivery rate of the exhaust gas, the pump being fitted in the exhaust gas pipe 5 in Fig. 3 and in the collecting return line 11 in Fig. 4.

The required flow rate of the partial stream of exhaust gases is set by a corresponding differential pressure; it results partly from utilizing the flow conditions, dynamic pressure and high pressure waves of the main exhaust gas stream and partly from diverting the partial stream of exhaust gases into the intake pipe 10, and also, where provided, from using the pump 12Orfromtheuseofvalves 13,14 and 15 (Figs. 5 and 6) which are in the form of butterfly valves and of which the valve 13 is arranged in the exhaust gas feed pipe 4 as shown in Figs. 5 and 6 and the valve 14 is arranged in the discharge pipe 6 (Fig. 5) or in the collecting return line 11 (Fig. 6). The embodiment shown in Fig. 5 avoids the need for a throttle.The partial stream of exhaust gases supplied in the.exhaust gas feed pipe 4 must, however, be greater than the partial stream of exhaust gases in the exhaust gas pipe 5 leading to the intake pipe 10 so that long-term operation of the filter 2 may be ensured.

The valve 13 in the exhaust gas pipe 4 is intended to open in response to high pressure peaks and the valves 14, 15to open in response to low pressure peaks so that the set throughflow of the partial stream of exhaust gases is dependent on the engine speed. The velocity of flow set in this manner enables an adequate flow of exhaust gases through the sensor so that an adequate control performance regarding the reduction of pollutants in the combustion gases may be achieved, for example in control systems in internal combustion engines operating according to the compression ignition and Otto cycles, as in the embodiments illustrated in Figures 1 to4.

The exhaust gas feed pipe 4 extends into the exhaust pipe 1 and is designed with a bend so that the inlet opening 16 is directed so that it faces towards the main exhaust gas stream whilst the outlet opening 17 of the discharge pipe 6 (fig. 5) and the outlet opening 18 of the collecting return line 11 (Figs. 4, 6), which also extend into the exhaust pipe 1 and are designed with a bend, so that they lie in the direction of flow of the main exhaust gas stream.

Claims

1. An exhaust system of an internal combustion engine having a filter and a sensor which detects the composition of the exhaust gases, wherein the sensoris located in a bypass system ofthe exhaust system.

2. An exhaust system according to Claim 1, wherein the sensor is provided in a separate sensor housing having heating means and is located at a predetermined distance downstream from the filter.

3. An exhaust system according to Claim 1 or Claim 2, wherein a partial stream of exhaust gases which is taken from the exhaust system can be fed downstream from the sensor either indirectly back to the internal combustion engine through an intake pipe or can be fed directly back into the main exhaust gas stream.

4. An exhaust system according to any one of Claims 1 to 3, wherein the filter comprises a discharge pipe which is provided for discharging filtered-off substances and which leads either back into the main exhaust gas stream orto the engine.

5. An exhaust system according to Claim 3 or claim 4, wherein a throttle is inserted in the discharge pipe.

6. An exhaust system according to any one of the preceding Claims, wherein a pump is provided downstream of the sensor.

7. An exhaust system according to any one ofthe preceding Claims, wherein a valve which opens in response to high pressure peaks is provided in the partial stream of exhaust gases leading to the filter, and a valve which opens in response to low pressure peaks is provided in the partial stream of exhaust gases or in the path of the filtered substances returning to the exhaust pipe.

8. An exhaust system according to any one of the preceding Claims, wherein the inlet opening of the exhaust feed pipe, which is provided for the partial stream of exhaust gases and is connected to the sensor, is directed towards the main exhaust gas stream in the exhaust gas steam in the exhaust pipe.

9. An internal combustion engine exhaust system substantially as herein before described and with reference to Figures 1, or Figure 1 modified as shown in any one of Figures 2 to 6 of the accompanying drawings.