Method and device for an EGR-system and a valve as well as a regulation method and device

The invention is related to a method and a device for recirculation of a part of exhaust gases from an exhaust pipe (6, 9) of a diesel engine (1) to the inlet of the engine, the exhaust gases being diverted from the exhaust pipe (6, 9) and directed through a recirculation conduit (10) to a controllable valve device (12) arranged between the engine and the air intake (2) thereof for allowing supply of air/recirculated exhaust gases in a desired relation to the combustion chamber of the engine (1). The invention also relates to a particular valve having two controllable inlets, said valve being useful in the method or device according to the invention, and a regulation method and device for regulating the air/fuel relation of a diesel engine.

The present invention is related to a method and a device for an EGR-system (Exhaust Gas Recirculation), particularly for use in heavy-duty diesel engines. The invention also relates to a valve which is particularly suited for the method and device according to the invention but the valve may also find use within other fields. Finally, the invention is also related to a regulation method and device for a diesel engine.

In order to reduce the contents of hazardous exhaust gases, particularly nitrogen oxide. (NOx), so called EGR-systems are used since many years in many types of combustion engines. Such systems admit a part of the exhaust gases to be recirculated to the intake system of the engine, where it is mixed with the intake air and is conveyed further to the combustion chamber of the engine. The recirculated exhaust gases replace a part of the intake air and have a reducing effect on the formation of NOx. A so called EGR-valve is then placed in connection with the exhaust system of the engine, the purpose of said valve being to regulate the amount of recirculated exhaust gases.

A method and a device according to the precharacterising parts of enclosed claims1and6are disclosed in DE A1 4 007 516. Although this prior art makes it possible to use an EGR-system in super charged diesel engines, where the pressure in the intake system downstream of the super charger is higher than the pressure in a recirculation conduit from an EGR-valve some important disadvantages are inherent in this prior art. Thus, the valve device comprises separate dampers arranged in the EGR-recirculation channel and an air intake channel. Separate drive motors are provided for these dampers, a fact which makes the valve device complicated and this also applies for a control device therefor.

OBJECT OF THE INVENTION

A primary object of the present invention is to provide a method enabling a more reliable and simple regulation of the relation air/recirculated exhaust gases. As to the device according to the invention, the aim is to simplify the valve device and provide for a more reliable and simple control thereof.

A secondary object of the invention is to provide a valve suitable for mixing two fluids flowing through two inlet channels. Such a valve should be suitable for general purposes but is particularly useful in an EGR-system for diesel engines, including super charged diesel engines.

A tertiary object of the invention is to provide a regulation method and device providing for improved regulation possibilities with regard to a diesel engine provided with an EGR-system.

SUMMARY OF THE INVENTION

The primary object of the invention is achieved by the features defined herein. The design of the valve device as comprising two dampers, where at least one of the dampers always is open and where the other of the dampers is closable by means of a drive motor common to the dampers provides for a simple design and a reliable operation.

The secondary object of the invention is achieved by means of the valve as defined herein.

The tertiary object of the invention is achieved by means of the regulation method and device as defined herein. Thus, this aspect of the invention is based on use of probes and sensors connected to a control device for the valve device so as to enable regulation not only of the relation air/recirculated exhaust gases but also regulation of the air/fuel relation of the engine.

This aspect of the invention provides for an improved overall regulation of the engine and a smaller amount of pollution.

Preferable developments of the basic aspects of the invention are defined herein.

The use of an EGR-system as contemplated by the invention on an engine provided with a catalyst and a particle filter according to the prior art results in a substantial reduction of the NOx contents. This reduction may be up to 50% and makes it possible to upgrade existing diesel engines to present emission requirements and to upgrade modern diesel engines to future emission requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by means of non-limiting embodiments illustrated in the drawings, where

FIG. 1illustrates a diagrammatical view of an EGR-system according to the invention;

FIG. 2aillustrates a sectioned valve according to the invention in one end position;

FIG. 2bis a section view of the valve inFIG. 2aas viewed in the direction of the arrow B—B;

FIG. 3aillustrates a sectioned valve according to the invention in an intermediate position;

FIG. 3billustrates a section view of the valve inFIG. 3aas viewed in the direction of the arrow B—B;

FIG. 4aillustrates a cut valve according to the invention in a second end position; and

FIG. 4billustrates a section view of the valve inFIG. 4aas viewed in the direction of the arrow B—B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1is a diagrammatical view showing the parts, which are essential to the invention, of a combustion engine indicated with the reference character1. The engine is in the selected embodiment example a turbo charged diesel engine but as already mentioned the engine may be a diesel engine without super charging or a diesel engine with a different type of super charging than a turbo charger. Air is taken to the engine1through an air intake, an air filter2, and is directed via an inlet air channel3to a turbo charger4, where the air is super charged and then conveyed further through an intercooler5, where the super charged air is cooled down before it is conveyed into the engine1. The exhaust gases from the engine1are first directed through the second side of the turbo charger4, namely that side which is the driving one, and then through an exhaust pipe6, a catalyst7and a particle trap8to finally be emitted to the open air via an end pipe9.

From the end pipe9, i.e. an extension of the exhaust pipe after the catalyst and particle trap, there is a branch, a recirculation conduit10, to recirculate from the exhaust gases a part thereof to the engine. The recirculation conduit10passes suitably through a cooler11to cool down the recirculated exhaust gases and it connects to the inlet air channel3via a valve device12controllable by means of an EGR control device13. The valve device12may, with the assistance of the EGR control device13, regulate the relation between the supplied amount of fresh air from the inlet air channel3and the supplied amount of recirculated exhaust gases from the recirculation conduit10.

The EGR control device13regulating the valve device12is supplied with information about the actual operational state of the engine from a.o. a Lambda probe14, a sensor15for the number of revolutions of the engine and a sensor16for engine load and this control device is programmed to control the valve device12and, accordingly, the mixing relation fresh air/exhaust gases for the purpose of minimising the contents of hazardous substances leaving the end pipe9and being emitted into the open air. The programming of the EGR control device13occurs in a previously known manner with regard to the relations between the different factors given hereinabove. As is well known, a Lambda probe provides an output signal varying with the oxygen contents of the exhaust gases. The engine load sensor16may for instance be a throttle position sensor and/or a sensor sensing the amount of fuel injected to the engine. Also other sensors than those mentioned may be added to achieve a refined regulation.

The valve device12may comprise separate valves in the inlet air channel3and in the recirculation conduit10, said valves then being separately controllable by the EGR control device13. Alternatively the valve device12may also comprise a unit, in which flows from the inlet air channel3and the recirculation conduit10may be selectively brought together, by means of valves contained in the valve device, to a common output flow, which is conveyed further to the turbo charger for super charging and introduction into the engine via the intercooler5. A particularly suitable valve device12in one unit is a particular part of the invention and will be described more closely hereunder.

The valve illustrated inFIGS. 2–4is a type of mixing valve providing for mixing of two in-flowing fluids in such a manner that the in-flowing fluid in one of the two inlet channels may be regulated from 0 to maximum, and thereafter the in-flowing fluid in the second inlet channel from a maximum to 0.

In use of the valve according to the invention as illustrated inFIGS. 2–4as a valve device12in the method or device according to the invention, the inlet air channel3is connected to the second inlet channel18of the valve, whereas the recirculation conduit10is connected to the first inlet channel17of the valve. Furthermore, there is in the valve an outlet channel19, which in the present embodiment conveys the gases mixed in the valve to the turbo charger4. In both inlet channels17and18, there are dampers20and21, which are pivotable between an open and a closed position by means of an adjustment motor22, for instance a step motor, to open or close the inlet channels. The two dampers20,21are placed on concentric axles23,24, which are rotatable by means of the adjustment motor22and an actuation pin25driven by the motor, said actuation pin being capable of pivoting actuation arms26,27connected to the axles23and24respectively. The actuation arms26,27are spring loaded by one or more springs28,29to a normal position, illustrated inFIG. 3, where both dampers20,21are held in a position such that the inlet channels17,18are open.

In the position illustrated inFIGS. 2a, b, which is a starting position, the adjustment motor22has, by means of its actuation pin25and by means of the actuation arm26, rotated the damper20to a closed position, and thus, the first inlet channel17connected to the recirculation conduit10is closed and no exhaust gases may be recirculated to the turbo charger and the engine. The second actuation arm27is maintained in its normal position by the spring29, which means that the damper21in the second inlet channel18connected to the inlet air channel3is maintained in its normally opened position and allows free flow of inlet air through the valve via the outlet channel19to the turbo charger. The adjustment motor22is controlled by the EGR control device13to regulate the relation between fresh air via the inlet air channel3and recirculated exhaust gases via the recirculation conduit10. In the position with the damper21open, the adjustment motor22may rotate, by means of its actuation pin25and by means of the actuation arm26, the damper20from the entirely closed position shown inFIGS. 2a, bto the position which is shown inFIGS. 3a, bwhere also the damper20is in such a position that also the first inlet channel17is open. The adjustment motor may also adjust the damper20into any position between these two end positions.

The position illustrated inFIGS. 3a, b, which is the normal position for the adjustment motor20, is such that the actuation pin25of the adjustment motor does not actuate any of the actuation arms26,27but they are maintained by the springs28,29in a normal position, where, accordingly, the dampers20,21open both inlet channels17,18.

FIGS. 4a, billustrates a position contrary to the one inFIGS. 2a, b. Thus, the adjustment motor22has by means of its actuation pin25and by means of the actuation arm27rotated the damper21to a closed position, which means that the connection of the inlet air channel3with the outlet channel19is entirely interrupted whereas on the contrary the first inlet channel17connected to the recirculation conduit10is entirely open and allows the recirculated exhaust gases to freely flow further through the outlet channel19and then to the turbo charger4and further on to the engine. However, by means of the adjustment motor22, the damper21may be adjusted into any intermediate position between the end positions illustrated inFIGS. 3 and 4to allow a desired amount, controlled by the EGR control device13, of fresh air to be mixed with the recirculated exhaust gases.

Thus, with the valve according to the invention it becomes possible to control, in a simple manner, a three-way valve having two inlets and having a normal position, where both inlets are open so that one or the other of the inlets may be controlled steplessly whereas the remaining inlet is maintained open. The valve may of course be controlled in other manners than by means of the EGR control device13described above and it may be used in quite different connections than the one now described and where corresponding control properties are desirable.

In a regulation method according to the invention, a control device is used which is supplied with information from a lambda probe14, a motor speed sensor15and an engine load sensor16. The control device is connected to a valve device, corresponding to the valve device12described here-inabove, for regulation of the in-flowing amounts of air and/or recirculated exhaust gases to the engine. This valve device is arranged between the air filter and the inlet channel of the engine and may, as also has been described for the valve device12, comprise separate valves in the inlet air channel and recirculation conduit, or a three-way valve of the kind also described hereinabove. The valve device is controllable in a corresponding manner as also described hereinabove, and the control device may therefore control, based on the input signals received, the air/fuel relation of the engine by regulating the amount of in-flowing air and simultaneously regulating the relation between the supplied fresh air and recirculated exhaust gases. This aspect of the invention is applicable with or without supercharging.

With the regulation method and device according to the invention it is possible to further decrease the NOx-contents in the exhaust gases exiting from the end pipe of a diesel engine.