METHOD OF REDUCTION OF EXHAUST GAS EMISSIONS FROM INTERNAL COMBUSTION ENGINES

Abstract: The invention relates to a method for reducing harmful and toxic exhaust gases from an internal combustion engine (1) which comprises at least one cylinder (2) to which an air/fuel mixture is supplied when a crankshaft (4) of the internal combustion engine (1) is to be made to rotate. The method comprises the following stages: an air/fuel mixture with a lambda value of greater than one is supplied to the cylinder (2), and the pressure in the intake channel (5) is controlled by means of an electric motor/generator (10) coupled to the crankshaft (4), so that when the pressure in the intake channel (5) exceeds a predetermined pressure, the electric motor/generator (10) is controlled in such a way that the pressure in the intake channel (5) can decrease, and when the pressure in the intake channel (5) falls below a predetermined pressure, the electric motor/generator (10) is controlled in such a way that the pressure in the intake channel (5) can increase.

Description: Method of reduction of exhaust gas emissions from internal combustion engines The present invention relates to a method for reducing harmful and toxic exhaust gases from an internal combustion engine which comprises at least one cylinder to which an air/fuel mixture is supplied when a crankshaft of the internal combustion engine is to be made to rotate. In internal combustion engines, it is desirable to reduce the harmful and toxic substances which occur in the exhaust gases of the internal combustion engine, in order thereby to reduce the burden on the surrounding environment and to comply with the legal requirements placed on internal combustion engines. The substances which occur in the exhaust gases include carbon monoxide CO, hydrocarbons HC and nitrogen oxides NOx. In order to reduce these substances from the exhaust gases, the internal combustion engine is provided with a catalytic converter which, by means of a chemical reaction, converts these substances to substances which do not adversely affect the surrounding environment. The chemical reaction in the catalytic converter occurs only when the catalytic converter has reached a predetermined working temperature, which is reached after a predetermined running time of the internal combustion engine. Therefore, when cold-starting the internal combustion engine, no reduction of the toxic substances takes place in the catalytic converter. Another problem which occurs when cold-starting internal combustion engines is that a relatively large amount of fuel in relation to the supplied air, i.e. a rich air/fuel mixture, must be supplied to the internal combustion engine for the internal combustion engine to be able to start and for the internal combustion engine to be able to operate at an essentially constant speed of rotation during idling. This rich air/fuel mixture is also supplied so that the internal combustion engine will be able to provide an increased torque upon acceleration. In this way, running of the internal combustion engine is guaranteed before the internal combustion engine has reached its operating temperature . The absence of the exhaust gas cleaning by the catalytic converter and the rich air/fuel mixture means that the levels of carbon monoxide CO, hydrocarbons HC and nitrogen oxides NOx emitted from the internal combustion engine are high upon cold-starting of the internal combustion engine. Attempts have previously been made to reduce the fuel quantity in relation to the air supplied, i.e. to drive the internal combustion engine with a leaner air/fuel mixture upon cold-starting of the internal combustion engine. However, this has meant that the internal combustion engine has worked very unevenly during idling, and that the drivability of the internal combustion engine has been poor. The reason why the speed of rotation varies during idling is that the torque provided by the internal combustion engine is very sensitive to variations in the lambda value of the air/fuel mixture supplied to the cylinder space of the internal combustion engine, when the air/fuel mixture is lean. The definition of the lambda value, or the air excess coefficient as it is also called, is the actual amount of air supplied, divided by the theoretically necessary quantity of air for complete combustion. If the lambda value is greater than one, the air/fuel mixture is lean, and if the lambda value is less than one, the air/fuel mixture is rich. It is possible to carefully control the fuel supplied from a fuel injection valve with the aid of the fuel injection system of the internal combustion engine, in order thereby to obtain an essentially constant lambda value for the air/fuel mixture supplied. When the internal combustion engine is cold, fuel will however condense on the comparatively cold walls in the intake channel and in the cylinder. The fuel condensed on the walls will evaporate during idling and follow the air/fuel mixture which flows into the intake channel and is supplied to the cylinder space. If the evaporation of the fuel condensed on the walls is uneven, on account of pressure changes, temperature gradients or the flow velocity of the air/fuel mixture in the intake channel, there will be a variation in the lambda value of the air/fuel mixture supplied to the cylinder space. Since the torque provided by the internal combustion engine will vary during idling upon a cold start, the speed of rotation of the internal combustion engine will also vary. The speed of rotation of the internal combustion engine here means the speed of rotation of the crankshaft of the internal combustion engine. When the speed of rotation varies, the pressure in the intake channel also varies, which in turn leads to the evaporation of the condensed fuel varying, so that there is a variation in the lambda value of the air/fuel mixture supplied to the cylinder space. The uneven speed of rotation of the internal combustion engine is thereby intensified. An object of the present invention is to reduce harmful and toxic exhaust gases from an internal combustion engine upon cold starts. Another object of the invention is to allow an internal combustion engine to operate with an essentially constant speed of rotation upon idling when a lean air/fuel mixture is supplied to the internal combustion engine. This is achieved by a method of the type specified in the introduction, comprising the following stages: an air/fuel mixture with a lambda value of greater than one is supplied to the cylinder, and the pressure in the intake channel is controlled by means of an electric motor/generator coupled to the crankshaft, so that when the pressure in the intake channel exceeds a predetermined pressure, the electric motor/generator is controlled in such a way that the pressure in the intake channel can decrease, and when the pressure in the intake channel falls below a predetermined pressure, the electric motor/generator is controlled in such a way that the pressure in the intake channel can increase. By controlling the pressure in the intake channels of the internal combustion engine with the aid of an electric motor/generator, the pressure in the intake channels can be maintained essentially constant. The lambda value of the air/fuel mixture supplied to the cylinders is thus maintained essentially constant, which means that the torque provided by the internal combustion engine will be essentially constant. The speed of rotation of the internal combustion engine will also be essentially constant, which means that harmful and toxic exhaust gases, in particular hydrocarbons, from the internal combustion engine decrease . The invention will be explained in greater detail below on the basis of an illustrative embodiment which is shown in the attached drawings, where: Fig. 1 is a diagrammatic representation of an internal combustion engine and an electric motor/generator for carrying out the method according to the present invention, Fig. 2 shows a flow chart representing the method according to the present invention, and Fig. 3 shows a diagram of the HC content in the exhaust gases, as a function of time, for an internal combustion engine which is driven using the method according to the present invention and for an internal combustion engine which is driven according to conventional methods. Fig. 1 is a diagrammatic representation of an internal combustion engine 1, which is provided with four cylinders 2. Arranged in each cylinder 2 there is a reciprocating piston 3 which is connected to a rotatable crankshaft 4. Connected to each cylinder 2 there is at least one intake channel 5. Only one intake channel 5 is shown in Fig. 1. Connected to the intake channels 5 there are fuel injection nozzles 6 which are controlled by a control unit 7. The control unit 7 is also coupled to a number of sensors 8 in the internal combustion engine 1, which sensors detect the temperature of the internal combustion engine 1, its speed of rotation, etc. It is also possible to arrange pressure sensors 9 in the intake channels 5 in order to detect the pressure in the intake channels 5. These pressure sensors 9 are connected to the control unit 7. An electric motor/generator 10, which functions as an integrated starting motor and generator (ISG), is coupled to the crankshaft 4 of the internal combustion engine 1. As a alternative to a direct coupling of the electric motor/starting motor 10 to the crankshaft 4, it is possible to use a belt, chain or gearwheel transmission for coupling the electric motor/generator 10 to the crankshaft 4. The electric motor/generator 10 is connected to a battery 12 via a control device 13. The control device 13 is connected to the control unit 7 and receives information from the control unit 7 on how the electric motor/generator 10 is to be driven. When the internal combustion engine 1 is in operation, air arrives at an intake manifold 14 via an air inlet pipe 15. From the inlet manifold 14, the air flows onwards to the intake channels 5 where the air is mixed with fuel which is injected into the intake channels 5 by means of the fuel injection nozzles 6. The air/fuel mixture then flows into the cylinders 2 and is ignited by an ignition plug (not shown) arranged in each cylinder 2. Lastly, the combusted air/fuel mixture in the form of exhaust gases runs off into the atmosphere through an exhaust gas system 16 connected to the internal combustion engine 1. As has been explained in the introductory part of the description, the combusted air/fuel mixture contains substances which can have an adverse effect on the surrounding environment. These substances include carbon monoxide CO, hydrocarbons HC and nitrogen oxides NOx. The exhaust gases are therefore treated in a catalytic converter 17 which is arranged in the exhaust gas system 16 and which converts these substances to substances which do not adversely affect the environment. However, the catalytic converter 17 functions only when it has reached a certain operating temperature, which is reached after a certain warming- up time after the internal combustion engine 1 has been started. Therefore, upon cold-starting of the internal combustion engine 1, no conversion of the abovementioned substances takes place in the catalytic converter 17. The amount of carbon monoxide CO, hydrocarbons HC and nitrogen oxides NOx in the exhaust gases depends, inter alia, on the mixing ratio of the air/fuel mixture supplied to the cylinders 2. This mixing ratio is usually indicated by a lambda value. The definition of the lambda value, or the air excess coefficient as it is also known, is the actual amount of air supplied, divided by the theoretically necessary amount of air. If the lambda value is greater than one, the air/fuel mixture is lean, and if the lambda value is less than one, the air/fuel mixture is rich. By supplying the cylinders 2 with an air/fuel mixture having a lambda value greater than one, i.e. a lean air/fuel mixture, when cold-starting the internal combustion engine 1, the level of hydrocarbons HC in the exhaust gases can be substantially reduced. If a lean air/fuel mixture is supplied to the internal combustion engine 1 when it is cold, i.e. when the internal combustion engine 1 has not reached its operating temperature, problems involving an uneven speed of rotation arise during idling, for the reason explained in the introductory part of the description. By controlling the electric motor/generator 10 so that the pressure in the intake channels 5 is maintained essentially constant, as is proposed according to the present invention, it is possible to achieve an essentially constant speed of rotation of the internal combustion engine 1 when the internal combustion engine 1 is cold and is being driven with an air/fuel mixture which is lean. The method according to the present invention will be explained below. When starting the internal combustion engine 1, the electric motor/generator 10 is first activated and thus drives the crankshaft 4 of the internal combustion engine 1. The electric motor/generator 10 functions as a starter motor for the internal combustion engine 1. At the same time, fuel and air, ignited in the cylinders 2, are supplied so that the crankshaft 4 is caused to rotate. In order to reduce the hydrocarbons HC which occur in the exhaust gases, the cylinders 2 are supplied with a lean air/fuel mixture having a lambda value of between 1.1 - 1.4, preferably between 1.1 - 1.2. However, when the internal combustion engine 1 is cold, fuel will condense on the comparatively cold walls in the intake channels 5. The fuel condensed on the walls is evaporated during idling of the internal combustion engine 1 and follows the air/fuel mixture which flows into the intake channels 5 and is supplied to the cylinders 2. The evaporation of the fuel condensed on the walls is uneven on account of pressure changes in the intake chanels 5. This results in a variation in the lambda value of the air/fuel mixture supplied to the cylinders 2. Since the torque provided by the internal combustion engine 1 will vary during idling at a cold start, the speed of rotation of the internal combustion engine 1 will vary. As has been mentioned above, the speed of rotation of the internal combustion engine 1 here means the speed of rotation of the crankshaft 4 of the internal combustion engine 1. When the speed of rotation varies, the pressure in the intake channels 5 also varies, which in turn leads to the evaporation of the fuel condensed on the intake channels 5 also varying, so that there is a variation in the lambda value of the air/fuel mixture supplied to the cylinders 2. The uneven speed of rotation of the internal combustion engine 1 is thus intensified. By controlling the pressure in the intake channels 5 with the aid of the electric motor/generator 10 coupled to the crankshaft 4, when the pressure in the intake channels 5 exceeds a predetermined pressure, the electric motor/generator 10 drives the crankshaft 4 in order thereby to reduce the pressure in the intake channels 5. This pressure reduction is achieved by means of the pistons 3 in the cylinders 2 generating an underpressure in the cylinders 2 during the intake stroke. The underpressure generated in the cylinders 2 will also be generated in the intake channels 5. When the electric motor/generator 10 drives the crankshaft 4, the speed of rotation of the crankshaft 4 increases, so that the underpressure generated in the cylinders 2 falls, which means that the pressure in the intake channels 5 falls. When the pressure in the intake channels 5 falls below a predetermined pressure, the crankshaft 4 drives the electric motor/generator 10 so that the speed of rotation of the crankshaft 4 decreases, which means that the pressure in the intake channels 5 increases. When the pressure in the intake channels 5 falls, the evaporation of fuel on the walls of the intake channels 5 increases. This leads to relatively more fuel being supplied to the cylinders 3 since the air/fuel mixture is richer. There is therefore an increase in the torque of the crankshaft 4, which also leads to an increased speed of rotation of the crankshaft 4. The electric motor/generator 10 will then take up this torque increase by means of the crankshaft 4 driving the electric motor/generator 10, which thus brakes the crankshaft 4. With this method, an essentially constant pressure can be obtained in the intake channels 5. A pressure sensor 9 can preferably be arranged in at least one of the intake channels 5 in order to measure the pressure in the intake channels 5. The pressure sensor 9 is coupled to the control unit 7 of the internal combustion engine 1, which control unit 7 sends signals to a control device 13 for the electric motor/generator 10. By controlling the pressure in the intake channels 5 of the internal combustion engine 1 with the aid of the electric motor/generator 10, the pressure in the intake channels 5 can be maintained essentially constant. The lambda value of the air/fuel mixture supplied to the cylinders 2 is thus maintained essentially constant, which means that the torque provided by the internal combustion engine 1 will be essentially constant. The speed of rotation of the internal combustion engine 1 is thus also essentially constant. Fig. 2 shows a flow chart representing the method according to the present invention. When the electric motor/generator 10 has started, it is possible, with the aid of the electric motor/generator 10, to rotate the crankshaft 4 of the internal combustion engine 1 through one or more turns, without fuel and air being supplied to the cylinders 2, for the purpose of generating an underpressure in the intake channels 5. This is generally referred to as the internal combustion engine 1 being cranked. When the air/fuel mixture is then supplied in order to start the internal combustion engine 1, more powerful evaporation of the fuel in the intake channels 5 will take place than would be possible if an underpressure had not been generated by cranking. The more powerful evaporation of the fuel leads to the hydrocarbons HC being reduced in the exhaust gases at the start-up time. The nitrogen oxides NOx also decrease at the start-up time on account of the fact that the combustion pressure in the cylinders 2 decreases as a result of the said cranking. When the combustion engine 1 is to be shut off, a temperature sensor 18 arranged on the catalytic converter 17 can detect the temperature of the catalytic converter 17. If the temperature of the catalytic converter 17 corresponds to or exceeds a predetermined temperature, the electric motor/generator 10 drives the crankshaft 4 for a period of time without fuel being supplied to the internal combustion engine 10, in order thereby to ventilate the fuel present in the intake channels 5 and the cylinders 2. The predetermined temperature corresponds preferably to the operating temperature of the catalytic converter 17. The fuel ventilated in the intake channels 5 and the cylinders 2 will be evaporated in the exhaust gas system 16 of the internal combustion engine 1, and hydrocarbons HC will be reduced in the warm catalytic converter 17. When the internal combustion engine 1 is next started up, there will therefore be no uncombusted fuel in the intake channels 5 and cylinders 2, which increases the level of hydrocarbons HC in the exhaust gases . Fig. 3 shows a diagram of the HC content, i.e. the content of hydrocarbons in the exhaust gases, as a function of time T, for an internal combustion engine 1 driven using the method according to the present invention and for an internal combustion engine driven according to conventional methods . The full line represents an internal combustion engine 1 driven using the method according to the present invention, and the broken line represents an internal combustion engine driven according to conventional methods. Tests have shown that the HC level is 5 to 10 times lower in an internal combustion engine 1 driven using the method according to the present invention than in an internal combustion engine driven according to conventional methods .

Claims: Patent Claims 1. Method for reducing harmful and toxic exhaust gases from an internal combustion engine (1) which comprises at least one cylinder (2) to which an air/fuel mixture is supplied when a crankshaft (4) of the internal combustion engine (1) is to be made to rotate, characterized in that the method comprises the following stages: an air/fuel mixture with a lambda value of greater than one is supplied to the cylinder (2), and the pressure in the intake channel (5) is controlled by means of an electric motor/generator (10) coupled to the crankshaft (4), so that when the pressure in the intake channel (5) exceeds a predetermined pressure, the electric motor/generator (10) is controlled in such a way that the pressure in the intake channel (5) can decrease, and when the pressure in the intake channel (5) falls below a predetermined pressure, the electric motor/generator (10) is controlled in such a way that the pressure in the intake channel (5) can increase. 2. Method according to Claim 1, characterized in that the pressure in the intake channel (5) is maintained essentially constant by means of the electric motor/generator (10) being controlled such that the crankshaft (4) rotates at an essentially constant speed of rotation. 3. Method according to Claim 1 or 2 , characterized in that the electric motor/generator (10) drives the crankshaft (4) for a predetermined time without fuel being supplied to the internal combustion engine (1), in order thereby to generate an underpressure in the intake channel (5) before the internal combustion engine (1) is started. 4. Method according to any of the preceding claims, characterized in that the temperature of a cataliser (17) arranged on the internal combustion engine (1) is detected, and if the temperature of the cataliser (17) corresponds to or exceeds a predetermined temperature, the electric motor/generator (10) drives the crankshaft (4) for a predetermined time without fuel being supplied to the internal combustion engine (1), in order thereby to ventilate fuel present in the intake channel (5) and the cylinder (2). 5. Method according to any of the preceding claims, characterized in that the internal combustion engine (1) is controlled by a control unit (7) which receives signals from the internal combustion engine (1) and which emits signals to a control device (13) for the electric motor/generator (10) . 6. Method according to any of the preceding claims, characterized in that the lambda value of the air/fuel mixture which is supplied to the cylinder (2) essentially lies in the range of 1.1 - 1.4 and preferably in the range of 1.1 - 1.2. 7. Method according to any of the preceding claims, characterized in that the method is essentially used for cold starting of the internal combustion engine (1) .

Inventors: ALMKVIST GOERAN, FREDRIKSSON KRISTER, ALMKVIST, GOERAN, FREDRIKSSON, KRISTER
Applicants: ALMKVIST GOERAN, FREDRIKSSON KRISTER, VOLVO AB, AB VOLVO, ALMKVIST, GOERAN, FREDRIKSSON, KRISTER
Application year: 2000
Main classification: F02D33
IPC codes: F02D41