GB2354722A

GB2354722A - Heatable catalytic converter

Info

Publication number: GB2354722A
Application number: GB0022708A
Authority: GB
Inventors: Martin Klenk; Andreas Posselt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-09-16
Filing date: 2000-09-15
Publication date: 2001-04-04
Anticipated expiration: 2020-09-15
Also published as: DE19944388A1; GB0022708D0; GB2354722B

Abstract

Exhaust emission control equipment for a motor vehicle with an internal combustion engine (10) and a fuel tank (27) comprises a catalytic converter 15 which is heatable during a heating phase without adding to fuel consumption. For this purpose, air is heated by combustion of fuel components volatilised from the fuel (40) in the fuel tank (27) and conducted through the converter (15). The air can be provided by a flushing air flow drawn through an activated carbon filter (26), which stores volatilised hydrocarbons vented from the tank, by an air pump (22) and fed to a burner (21), which is integrated in the converter (15), via a flow control valve (24) open during a converter heating phase.

Description

2354722 EXHAUST EMISSION CONTROL EQUIPMENT The present invention relates

to exhaust emission control equipment, especially equipment providing rapid heating up of a catalytic converter in a motor vehicle with an internal combustion engine and a fuel tank.

In known equipment of this kind (DE 44 45 971 Al), secondary air injection, in which compressed air is conducted in directly in front of the hot exhaust valves of the internal combustion engine, is used for heating up the catalytic converter. This secondary air injection leads to oxidation and thus to decomposition of the hydrocarbons in the exhaust gas, which contributes to reduction in the noxious exhaust gas constituents and effects, through the arising oxidation heat, an accelerated heating up of the catalytic converter, in which an appreciable conversion of the noxious substances in the exhaust gas takes place from only about 2500C and the ideal operating conditions of which for high conversion rates and long service life lie at about 400 to 8000C. The injection of secondary air is carried out by means of a secondary air pump, which is connected with a secondary air duct, for conveying the air flow and building up a conveying pressure, a control valve for selectable switching on and off the secondary air flow and a non-retum valve which prevents the exhaust gas from passing to the control valve against the conveying direction of the secondary air pump. The secondary air duct ends in individual feed ducts which in turn open into individual outlet channels of the engine downstream of each exhaust valve. An electronic control device evaluates the operating parameters, for example the lambda value, of the engine and controls the operation of secondary air pump and control valve.

The fuel storage tank of a motor vehicle is, for reasons of a reduced environmental loading, frequently equipped with a device for collecting components of the fuel volatilising from the fuel in the tank, as described in, for example, DE 35 19 292 C2. These volatilised fuel components, principally highly volatile hydrocarbons, are stored in an activated carbon filter and subsequently fed for combustion to the engine. In that case, the activated carbon filter is received in a filter housing, which has an outlet and two inlets. The first inlet is connected with the vent of the fuel tank and the second inlet continues in an air feed pipe. The outlet is connected with the induction duct of the engine by way of a controllable electromagnetic delivery regulation valve, wherein the connecting duct opens upstream of the throttle flap present in the induction duct. The regulating valve is controlled by an electronic control device. In the open state of the delivery regulation valve, flushing air is 2 sucked through the filter by the underpressure prevailing in the induction duct via the air feed stub pipe of the filter housing and entrains the volatilised fuel components deposited in the activated carbon filter and thus regenerates the activated carbon filter. The air, enriched with the fuel components and metered by the delivery regulating valve is conducted together with the air-fuel mixture into the cylinders of the engine.

According to the present invention there is provided a device for rapid heating up of a noxious substance catalytic converter in a motor vehicle with internal combustion engine and fuel tank, characterised in that during catalytic converter heating phases air is heated by combustion of fuel components volatilised from the fuel reserve in the fuel tank and is conducted through the converter.

Emission control equipment embodying the invention may have the advantage that the catalytic converter is directly and thus rapidly heated up by means of hot combustion gases, and the highly volatile hydrocarbon portions, which volatilise from the fuel in the fuel tank, are used for that purpose. Thus, a high conversion rate of the exhaust gas in the converter is achieved very soon after starting of the engine or after a cooling down of the converter that has taken place during a longer idling or overrun operational phase. No fuel for combustion is needed for heating the converter, so that fuel consumption does not rise. As the activated carbon filter is almost completely emptied in the converter heating phases, which are always triggered in the case of an under- temperature of the converter after, for example, a longer period of idling or overrun operation of the engine, the risk of overflow of the filter and the frequency of flushing of the filter during travel can be significantly reduced. The hydrocarbon emission of the engine is decreased overall.

According to an advantageous embodiment of the invention, the combustion takes place in a burner which is integrated in the converter at the inlet side and to which an air flow enriched with volatilised fuel components is fed by way of a control valve open only in the catalytic converter heating phase.

In a preferred embodiment the air flow is a flushing air flow led by means of an air pump through an activated carbon filter in which fuel components volatilised from the fuel tank can be deposited, wherein advantageously the activated carbon filter is received in a filter housing which has a first inlet opening connected by way of a first blocking valve with a ventilating stub pipe of a fuel tank, a second inlet opening connected by way of a second 3 blocking valve with an air feed stub pipe, and an outlet opening connected with the suction inlet of the air pump.

The feed and preparation of the volatilised fuel components can take place in, for example, two different ways. In a first example, the control valve is arranged between the pressure outlet of the air pump and the burner, and the air pump, the control valve and the blocking valves are controlled by a control unit in such a manner that during the converter heating phases the air pump is switched on, the control valve and the second blocking valve are opened and the first blocking valve is closed. In this system design the substantial part of the fuel components stored in the activated carbon filter are flushed out during the heating phases and combusted in the burner.

In a second example, the control valve is arranged between the burner and a device, which is connected with the pressure outlet of the air pump, for condensing and storing the fuel components flushed out of the activated carbon filter. The air pump, which is arranged between the outlet opening of the filter housing and the condensing and storing device, the control valve and the blocking valves are controlled by a control unit in such a manner that in travel operation outside the converter heating phases when the control valve is constantly closed the air pump is switched on, the second blocking valve opened and the first blocking valve closed, and conversely the air pump is switched off and the blocking valves opened, at intervals in alternation. During the converter heating phases the control valve is opened and, with activated burner, the air pump is switched on. The first blocking valve is closed and the second blocking valve remains open. In the case of this system design, the highly volatile fuel components stored in the filter are flushed out during normal travel operation so as to be condensed and stored in the condensing and storing device and are blown out of the device by the flushing air flow during the heating phases and combusted in the burner.

In both cases it is advantageous to admix to the air flow, which is fed to the burner and is enriched with volatilised fuel components, supplementary air which is preferably branched off by a secondary air pump which is usually present in the engine installation. By virtue of this air excess an ignitable fuel-air mixture and a sufficiently large gas quantity for heating of the converter is produced in the burner.

4 In the case of the afore-mentioned intermediate deposit of the highly volatile fuel components, which are flushed out of the filter during travel operation, in the condensing and storing device the flushing air flow through the activated carbon filter can also be produced, if an additional air pump is not provided, by means of an underpressure, to which, in the case of an engine with induction duct injection, the induction duct underpressure is referred. A flushing air valve is arranged between the outlet opening of the filter housing and the condensing and storing device, which is connected at the outlet side on the one hand with an underpressure duct and on the other hand with the control valve. In the converter heating phases the flushing air valve is closed and a suction flow, which is charged in the condensing and storing device with the fuel components stored therein, is fed, led by way of the condensing and storing device, to the burner. This suction flow is preferably produced by a secondary air pump of the engine, which pump serves for reduction in the noxious substance emission and is connected at the outlet side by way of a branch duct with the burner and blows supplementary air into the burner.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic diagram of an engine fitted with first exhaust emission control equipment embodying the invention; Fig. 2 is a schematic diagram of an engine fitted with second exhaust emission control equipment embodying the invention; and Fig. 3 is a schematic diagram of an engine fitted with third exhaust emission control equipment embodying the invention.

Referring now to the drawings there is shown in each of Figs. 1 to 3 an internal combustion engine 10 with a combustion cylinder 11 containing a working piston 12, inlet valve 13 and an exhaust valve 14. The exhaust valve 14 is connected with an exhaust pipe 39, in the course of which a three-way catalytic converter 15 is arranged. Operating parameters are detected by means of sensors 16 and 17 and fed to a control device 19, which, inter alia, controls in dependence on these operating parameters the ignition in the cylinder 11 and the injected fuel quantity and for this purpose is connected with fuel injection valves 18 and an ignition device 20 present in the head of the cylinder 11.

For reducing the noxious substance emission in the exhaust gas there is provided a secondary air pump 42 as described in the introduction. The secondary air pump 42 is, as known, connected by way of a secondary air duct 43, which is divided into individual feed ducts 49, with the individual exhaust manifold ducts of the engine downstream of the exhaust valves 14. The feed ducts 49 are controlled by a secondary air switching valve 50.

A recombustion of the exhaust gases and thus a lowering of the noxious substances in the exhaust gas takes place in the catalytic converter 15. The conversion rate of the converter 15 in that case depends quite substantially on the operating temperature, wherein an appreciable conversion of the noxious substances arises only from about 2500C. The ideal operating condition for the converter 15, with high conversion rates and long service life, occurs at about 400 to 800 OC. In order to achieve these ideal operating conditions as soon as possible after starting the engine 10 or after cooling down of the converter 15 during a longer period of idling or overrun operation of the engine, there is provided a device which is illustrated in block circuit form in Figs. 1 to 3 and which rapidly heats up the converter 15 in a heating phase following each starting of the engine or each cooling down of the converter and brings it to the desired operating temperature.

The heating-up device illustrated in Fig. 1 comprises a burner 21 integrated in the catalytic converter 15 at the inlet side, an air pump 22, which is connected with the burner 21 by way of a feed duct 23, a control valve 24, which is arranged in the feed duct 23 and preferably has the form of an electromagnetic valve, and a filter housing 25 with an activated carbon filter 26, to which the air pump 22 is connected at the suction side, for collecting fuel components (hydrocarbons) volatilising from the fuel 40 for the engine 10. The fuel is received in a fuel tank 27 with a filler pipe 28, which is hermetically closed by a tank cap 41, and a vent pipe 29. The latter is connected by way of a connecting duct 30 with a first inlet opening 31 of the filter housing 25. A first electromagnetic blocking valve 32 is arranged in the duct 30. The housing 25 has a second inlet opening 33, which is formed at the housing wall opposite the first inlet opening 31 and is connected by way of a second electromagnetic blocking valve 34 with an air feed pipe 35 opening into the ambient atmosphere. Provided in the filter housing 25 in the housing wall opposite the second inlet opening 33 is an outlet opening 36 which is connected by way of a suction 6 duct 37 with the suction inlet of the air pump 22. The air pump 22, the control valve 24 and the two blocking valves 32 and 34 are controlled by the electronic control device 19.

In travel operation with the catalytic converter 15 sufficiently warm the air pump 22 is switched off, the control valve 24 closed, and the first and second blocking valves 32, 34 are opened. The fuel components (principally highly volatile hydrocarbons) volatilising from the fuel 40 in the fuel tank 27 pass by way of the open connecting duct 30 into the filter housing 25 and are deposited in the activated carbon filter 26. If the converter is below temperature, thus directly after the start of the engine 10 or after a cooling-down phase, a converter heating phase is initiated, in which a flushing air flow enriched with the fuel components from the activated carbon filter 26 is fed to the burner 21. For this purpose the air pump 22 is switched on by the control device 19, the control valve 24 opened and the first blocking valve 32 blocked. Air is sucked by way of the open second blocking valve 34 through the filter 26 and flushes the fuel components out of the filter. This flushing air flow enriched with the volatilised fuel components then passes by way of the opened control valve 24 into the burner 21, which is activated by the control device 19 and combusts the fuel-enriched flushing air. In that case the converter 15 quickly reaches the desired operating temperature of more than 2500C.

In order to obtain an ignitable fuel-air mixture in the burner 21 and a sufficiently large, heated gas quantity through air excess, an additional air quantity delivered by the secondary air pump 42 is fed to the burner 21. For this purpose there is branched off to the burner 21 from the secondary air duct 43 a branch duct 44 which is controlled by a secondary air valve 45 opened only during the converter heating phases.

In the embodiment illustrated in Fig. 2, the device for heating up the converter 15 differs from the afore-described device of Fig. 1 only to the extent that a device 38 for condensing and storing the volatilised fuel components flushed out of the activated carbon filter 26 is arranged in the pressure duct 23 between the air pump 22 and the burner 21. This condensing and storing device 38 is connected into the feed duct 23 between the control valve 24 and the pressure outlet of the air pump 22 and is provided with a relief opening 46 communicating with the ambient atmosphere. The highly volatile fuel components stored in the activated carbon filter 26 are flushed out by the flushing air flow, which is generated by the air pump 22, during normal travel operation (outside the catalytic converter heating phases) and conducted into the condensing and storing device 38. For 7 this purpose the control device 19 switches on the air pump 22 at time intervals and closes the first blocking valve 32 so that the flushing air flow flows through the open second blocking valve 34, the filter 26 and the air pump 22 into the device 38. The highly volatile fuel components are condensed and stored therein, whilst the air flows away via the relief opening 46. In the intermediate time intervals in which the air pump 22 is switched off, the first and second blocking valves 32, 34 are opened so that the volatilising fuel components pass to the filter 26 and can deposit therein. The control valve 24 remains closed outside the converter heating phases. During the converter heating phases the burner 21 and the air pump 22 are switched on, and the control valve 24 opened, by the control device 19, whilst the second blocking valve 34 remains opened. The highly volatile fuel components condensed and stored in the device 38 are fed to the burner 21 together with the flushing air flow, which is delivered by the air pump 22 and flows through the filter 26 and which is similarly charged with volatile fuel components, and are used for heating the converter 15.

The form of heating-up device shown in Fig. 3 differs from that according to Fig. 2 in that the flushing air flow through the filter 26 is produced not by an air pump, but by an underpressure. In the case of an engine with induction duct injection the condensing and storing device 38, which is arranged upstream of the control valve 24 in the feed duct 23, is for that purpose connected by way of a further outlet with an underpressure duct 47 leading to the induction duct of the engine. A flushing air valve 48, which is controlled similarly to the other valves 24, 32 and 34 by the control device 19, is arranged between the outlet opening 36 of the filter housing 25 and the inlet of the condensing and storing device 38. As in the case of the embodiment of Fig. 2, the flushing of the filter 26 takes place in time intervals during the travel operation outside the converter heating phases, in that a flushing flow produced by the induction duct underpressure is sucked, by way of the air feed pipe 35, through the filter 26 and by way of the opened flushing air valve 48. The suction flow flows through the device 38 and the major part of the volatilised fuel components contained in the flushing air flow is condensed and stored. In the converter heating phases the flushing air valve 48 is closed and the control valve 24 opened, and the secondary air valve 45 opened, by the control device 19. The secondary air fed to the burner 21 by way of the branch duct 44 produces a suction air flow, which flows by way of the relief opening 46 and through the device 38 by way of the opened control valve 24 to the burner 21 and which entrains, and transports into the burner 21 the intermediately deposited fuel components. Consequently, there is provided an ignitable fuel-air mixture 8 which cornbusts and makes available a sufficiently large hot gas quantity for the heating of the converter 15.

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Claims

Exhaust emission control equipment for a motor vehicle, comprising a catalytic converter heatable during a heating phase and means for heating air by combustion of fuel components volatilised from fuel in a fuel tank of the vehicle and heating the converter by the heated air.
2. Equipment as claimed in claim 1, wherein the means for heating air comprises a burner integrated in the converter at an exhaust gas inlet thereof and connected to supply means for supplying to the burner an air flow enriched with the volatilised fuel components.
3. Equipment as claimed in claim 2, the supply means comprising a flow control valve openable only during the heating phase.
4. Equipment as claimed in claim 3, the supply means comprising an activated carbon filter for collecting the volatilised fuel components and air feed means for feeding air to the filter to provide a flushing air flow for removal of the components from the filter.
5. Equipment as claimed in claim 4, wherein the filter is housed in a housing having a first inlet connectible by way of a first blocking valve with a vent of the tank, a second inlet communicable by way of a second blocking valve with the ambient atmosphere to form the air feed means and an outlet for the flushing air flow with entrained fuel components.
6. Equipment as claimed in claim 4 or claim 5, comprising a condensing and storing device for receiving the flushing air flow and condensing and storing the fuel components, the device having a relief opening communicating with the ambient atmosphere.
7. Equipment as claimed in claim 5, comprising conveying means connected with the outlet of the housing and operable to convey the flushing air flow directly to the burner.
8. Equipment as claimed in claim 7, comprising a control unit to so control the flow control valve, blocking valves and conveying means that during the heating phase the control valve and second blocking valve are open, the first blocking valve is closed and the conveying means is in operation.
9. Equipment as claimed in claim 6, comprising conveying means connected with the outlet of the housing and with air inlet of the condensing and storing device, the flow control valve being connected with an outlet of the device and an inlet of the burner to permit flow of air charged with fuel components to the burner.
10. Equipment as claimed in claim 9, comprising a control unit to so control the flow control valve, blocking valves and conveying means that during the heating phase the control valve and second blocking valve are open, the first blocking valve is closed and the conveying means is in operation and during engine operation outside the heating phase the control valve is closed, the second blocking valve is open and the pump is placed in operation and taken out of operation at intervals in alternation, the first blocking valve being closed when the pump is operating and open when the pump is not operating.
11. Equipment as claimed in any one of claims 2 to 10, comprising means for feeding supplementary air to the burner.
12. Equipment as claimed in claim 6, comprising a flushing air flow valve for controlling the flushing air flow from the filter to the device, the device being so connectible at outlet rneans thereof with a source of underpressure and with the flow control valve that the flushing air flow is produced by underpressure and is fed to the burner by way of the control valve.
13. Equipment as claimed in claim 12, comprising a control unit to so control the flow control valve, blocking valves and flushing air flow valve that during the heating phase the control valve is open and the flushing air valve is closed and during engine operation outside the heating phase the control valve is closed, the second blocking valve is open and the flushing air flow valve is opened and closed at intervals in alternation, the first blocking valve being closed when the flushing air flow valve is open and being open when the flushing air flow valve is closed.
14. Equipment as claimed in claim 12 and 13, wherein the underpressure producing the flushing air flow is provided by means for feeding supplementary air to the burner.

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15. Equipment as claimed in claim 11 or 14, wherein the means for feeding supplementary air comprises a secondary air pump connected with the burner by way of a valve which is open only during the heating phase.
16. Exhaust emission control equipment substantially as hereinbefore described with reference to any one of Figs. 1 to 3 of the accompanying drawings.
17. A motor vehicle with an internal combustion engine and emission control equipment as claimed in any one of the preceding claims.