SE524515C2 - Arrangement for exhaust gas feedback in internal combustion engine incorporates adjustable venturi device for feeding exhaust gases into engine inlet conduit - Google Patents

Abstract

The arrangement for exhaust gas feedback in an internal combustion engine incorporates an adjustable venturi device (9) for feeding exhaust gases into engine inlet conduit (2). The venturi device includes a fixed venturi housing (8) and a movable venturi insert (10), and, for its adjustment, a pneumatic cylinder (21) activatable in one direction by compressed air and in another direction by a return spring. The pneumatic cylinder is formed so that it can bring the venturi insert to both a distinct intermediate position (10) and to its end position. The invention also includes a suitable internal combustion engine and a method for exhaust gas feedback.

Description

As a prior art with respect to the present invention, mention may also be made of WO Ol / 90559, where the flow effect can be varied by a venturi insert movable in the venturi device. In this way, both the quantity and the time of the return can be optimized. It also makes it possible to minimize flow losses as dampers and similar control devices become unnecessary.

A problem with the above configuration is that in certain operating cases an optimal mixture of exhaust gases is not obtained, which can lead to increased emissions of harmful compounds, such as NOX.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a solution to or reduction of the problems of the prior art. A main purpose is thus to reduce the emission of harmful compounds, in the event of a larger number of operating cases of the engine.

According to the invention, this is achieved in a device of the kind mentioned in the introduction by the features stated in the characterizing part of claim 1.

The invention reduces the emissions of harmful compounds in a large number of operating cases for the engine, by providing increased possibilities to control the venturi insert with simple means. This is done in such a way that the pneumatic cylinder is designed to bring the venturi insert to a distinct intermediate position, whereby the return of exhaust gases is optimized for counter- This means that the total emission of corresponding operating cases. harmful compounds during the entire operation of the engine are reduced. 71780; 2002-12-20 l5 a: å5 ~ I | - u ...

E 5 5 v .. u. V. . . 4 1 - u ..., '__' O t: u ». n. n: - av uo o u -,, ': - o u n. -. ; In a first aspect of the invention, the Venturi insert is brought to a distinct intermediate position by providing the pneumatic cylinder with two chambers each comprising a piston, and with an air intake to each chamber.

In this first aspect of the invention, compressed air with a pressure level can be used. Conveniently, the two chambers of the pneumatic cylinder are pressurized by two on / off valves.

In order to bring the Venturi insert to a distinct intermediate position, in a second aspect of the invention a modified pneumatic cylinder is used, which comprises spring return means with different spring constants according to their length.

In this second aspect of the invention, compressed air is used for the pneumatic cylinder with two different pressure levels. A first lower level for guiding the piston of the cylinder to a distinct intermediate position and a second level for guiding the piston to its pressurized end position. These two different pressures can be achieved by using a proportional valve or two on / off valves, which. controls two different pressures. The venturi insert can be designed so that for the open position the cylinder is inactivated, for an intermediate position the cylinder is under medium pressure, and for the closed end position the cylinder is under higher pressure.

It is preferred that this is realized by inserting two return springs, which are of different lengths in order to obtain the distinct intermediate position of the piston of this pneumatic cylinder.

Further features and advantages of the invention will become apparent from the following descriptive examples. vivso; zooz-12-zc _ YH s 524 515 _, 4 DRAWING DESCRIPTION Embodiments exemplifying the invention will now be described with the aid of the accompanying drawings, in which: Fig. 1 schematically shows an internal combustion engine provided with a venturi device according to the invention for exhaust gas recirculation, Fig. 2 shows more in detail the venturi device provided with a movable venturi insert, Fig. 3 shows a pneumatic cylinder according to a first embodiment for regulating the venturi insert, where the piston of the cylinder is in a non-pressurized, inactivated position, Fig. 4 shows a pneumatic cylinder according to the Fig. 5 shows a pneumatic cylinder according to the first embodiment, where the piston of the cylinder is in a pressurized intermediate position, Fig. 6 shows a pneumatic cylinder according to a second embodiment, wherein the pneumatic cylinder comprises a first and a second piston, both pistons being in a non-three Fig. 7 shows the pneumatic cylinder according to the second embodiment, the first piston being in a pressurized position, Fig. 8 shows the pneumatic cylinder according to the second embodiment, the second piston being in a pressurized, activated position.

DESCRIPTION OF EMBODIMENT 71780; 2002-12-20 b3 .. 'U1 .ri s h. U. O. _ 524 515. ~ ... @, _.... . . . n l u n v. ,,. _ an 4 ~ n o 4 u, u. . . _ ': .v u.

I, 3: v ..,. _ v ~ | . .. u. n .. -. . . Fig. 1 schematically shows an internal combustion engine type 1 combustion engine 1 with cylinders arranged in a straight cylinder bank. In this example, the engine is a supercharged four-stroke diesel engine intended, for example, for a heavier vehicle such as a truck or a bus.

The engine is equipped with a supercharger in the form of a turbocharger comprising a compressor C and an exhaust turbine T.

Inlet air to the engine is led via an inlet line 2 to an inlet manifold 2a from where the inlet air is distributed to the respective cylinder in the engine. The inlet line comprises a charge air cooler 5 and a venturi device 9 where the venturi device is arranged on the inlet line 2 between the charge air cooler 5 and the inlet manifold 2a. Exhaust gases from the engine cylinders are collected in an exhaust gas collector 3a from where these are led via an exhaust line 3 to the exhaust turbine T.

The exhaust line 3 and the inlet line 2 are connected to each other via a transfer channel 4 which at the inlet line opens into the venturi device 9. The transfer channel 4 comprises an EGR control valve 6 for regulating the flow through the transfer line and an EGR cooler 7 for cooling the returned exhaust gases.

The venturi device 9 comprises a throttle which is controllable under the influence of a control system S, suitably in the form of a computer, and which control system regulates the throttle in dependence on engine parameters. The venturi device influences the inlet air that during the passage through the throttle a speed increase is given which results in the formation of a negative pressure zone, at which exhaust gases from the transfer duct 4 can be initiated and mixed with the inlet air. 71780; 2002-12-20 i! n. n. . _, 4 5 1 5 'I I o n n a .nu l "' '' 'N. - n p...."' ° ~ n 1 nu o u p I,, _ 'U u u. _ ': o 1 f. . , '' I - -. . . .

I. ... . »-. u u .. _ 6 Fig. 2 shows the venturi device 9 in more detail. An adjustable venturi insert 10 is rotatably attached to a hinge 26 and is shown in a maximum position 'with solid lines brought into the inlet line 2, in an intermediate position 10 "with dashed lines and in a position 10'" made maximum from the inlet line 2 with dashed lines when the venturi insert 10 is instead housed in a recess 27 in a venturi housing 8.

The positions of the venturi insert 10 are controlled under the influence of the control system S (Fig. 1) by means of an intended adjusting member 21 which is mechanically connected to the venturi insert. The venturi housing 8 in this way comprises a channel with a substantially square cross-sectional shape where the side walls are parallel to each other and where the venturi insert cooperates with an opposite flat wall in the inlet pipe 2. The venturi insert itself comprises substantially two planes connected to each other at a certain angle. . Arrow R indicates the flow direction in the inlet line 2. The transfer channel 4 opens approximately in the middle of the part of the venturi device 9, where the greatest negative pressure prevails.

Control of the amount of exhaust gases to be returned takes place by means of the control system S (Fig. 1), which in a manner known per se communicates with sensors for sensing suitable engine parameters. The figure also shows an adjusting member 21, which is controlled by the control system S (Fig. 1). In the present invention, the actuator is a pneumatic cylinder capable of occupying a distinct intermediate position corresponding to a distinct intermediate position 10 "in addition to the end positions 10 'and 10"' of the venturi insert.

Fig. 3 shows a pneumatic cylinder 21 according to a first embodiment of the invention. The cylinder 21 is provided with a working chamber 24 and a compressed air inlet 25. Furthermore, the cylinder 21 is provided with a piston 22 and spring return means in the form of 71780; 2002-12-20 Üäo 524 515 7 - =. . - «« o -. v u »e - u .- two return springs ll, 12, the first spring ll being longer in the axial direction than the second 12. In this figure the cylinder is not pressurized, and the two springs in their most extended positions.

When the cylinder is pressurized with a first pressure at a first level, as shown in Fig. 4, the piston 22 moves inwards in the cylinder 21 and is able to compress the first spring 11 to a position where the piston meets the second spring 12. Now spring increases the force on the piston is abrupt, as it abuts both springs, so the piston stays in a distinct intermediate position, where equilibrium prevails.

To bring the piston to its pressurized end position, the air pressure is further increased to a second pressure at a second level in the cylinder 21, as shown in Fig. 5. Here full pressure is applied, the two springs are maximally compressed and the piston 22 is in its pressurized end position.

A suitable level of the first pressure is cza 1-2 bar, while a suitable level of the second pressure is cza 5-8 bar.

By having a significant separation between the pressure levels, greater opportunities are obtained to obtain the desired intermediate position more precisely.

In another, not shown, variant of this first embodiment of the invention, a pneumatic cylinder with spring return means in the form of only one spring can be used. In order to achieve the distinct intermediate position, the spring is designed in such a way that it has a varying spring constant along its length. For example, the spring may have a first spring constant in a portion closest to the piston and a second spring constant in another portion. If the spring is designed in a suitable, tuned manner, 71780; 2002-12-20 '.n5 w v .. n.. . H n ß -n n. I n n u n u en v.., Z ': u. u n o 'v n- o. u.,,, 0 n u. v o q v n,. , '' '' ° 1 u ... n n -. a n | . . . ., 8 the behave as follows. When the spring is compressed, at a low pressure, the main compression takes place in the part of the spring with a low spring constant. At a certain pressure this part of the spring is compressed, while the other part is not appreciably compressed. A distinct intermediate position arises in this way. If the spring is divided into more than two areas with different spring constants, the piston can be made to assume several distinct positions at the corresponding differential pressurization.

The varying spring constant can be achieved e.g. by varying the thickness, pitch, degree of hardening or material of the spring.

Yet another variant, not shown, of this first embodiment is a pneumatic cylinder with more return springs than two. With several springs, several distinct positions can be achieved, in a manner analogous to that described above for two return springs.

Fig. 6 shows a pneumatic cylinder 21 according to a second embodiment of the invention. The cylinder is here provided with two chambers 16, 17 with associated pistons 14, resp. 15 and to these chambers each have an inlet for compressed air 18, 19. The first piston 14 and the chamber 16 may, for example, be annular. The cylinder is shown here in a non-pressurized position.

When the first chamber 16 is pressurized with compressed air through the inlet 18, the piston 14, as shown in Figure 7, moves until it comes into contact with a stroke-limiting projecting member 20. The stroke of the piston 14 is thus limited in the axial direction. During this movement, the piston 14 pushes the second piston 15 forward to the position where the first piston 14 contacts the projecting means 20 and 71780; 2002-12-20 .'-: 3o n u I ø .a u ..- '' - Q. | ,, 9 thus occupies its end position. The second piston 15 then assumes a distinct intermediate position. Preferably, the axial position of the member 20 is adjustable to obtain a desired intermediate position.

If the second chamber 17 is pressurized via the second inlet 19 for compressed air, as shown in Figure 8, the second piston is brought to its pressurized end position due to its stroke length exceeding the stroke length of the piston 14.

An advantage of this second embodiment of the invention is that only compressed air with a single pressure needs to be provided, whereby the compressed air can easily be controlled out with two on / off valves.

It is desirable to have an exhaust gas mixture of about 10%, even if other admixture proportions are not excluded. This results in a slower combustion and thus a smaller amount of unwanted compounds, e.g. NOX, in the exhaust gases. At different loads and speeds of the engine, the inlet gas flow to it varies. To compensate for this, the venturi insert is varied in such a way that at low inlet gas flow, corresponding to low load for the engine, the venturi insert is largely inserted in the line and vice versa for high inlet gas flow, corresponding to high load for the engine.

In the case of a heavy vehicle, a large part of the engine's operating time takes place at an inlet gas flow, which is between the lowest and the highest flow of the engine, this intermediate position corresponding to approximately 1500 rpm or approximately 50-80% load. An example of such operation is motorway driving at high speeds on smooth roads. Achieving optimal conditions at this operating condition would thus lead to an improved overall efficiency and decreased 71780; 2002-12-20 524 515 emissions during this operation. This is achieved according to the invention by bringing the venturi insert to a distinct intermediate position in the manner shown. It should be noted that "intermediate position" refers to a position between two end positions and not necessarily a middle position. Physically, at the intermediate position of the venturi insert, for example, there may be 25% left to the closed end position, corresponding to the pressurized end position of the cylinder.

Adjustment of the distinct intermediate position to the desired operation can be easily done by designing the dimensions of the cylinder and, where applicable, the length of the return springs.

Controlling the venturi insert with a pneumatic cylinder is advantageous from many points of view, and compressed air is often already available in the applications where the engine is used, and the pneumatic cylinder is compact and simple in construction, which makes it reliable, reliable and economical. advantageous.

Of course, it is possible to control the venturi insert proportionally, with an ordinary pneumatic cylinder, with a single spring with one and the same spring constant over its working length, and a means for positional feedback of the position of the venturi insert.

However, it means a more complicated and expensive solution, which is not preferred.

It should be mentioned that the end positions of the respective cylinder can be reversed, so that the pressureless end position of the cylinder corresponds to the venturi insert being maximally inserted into the inlet line 2 and the pressurized end position corresponds to it being maximally removed from the inlet line 2. 71780; 2002-12-20 1 ... 524 5153-- v 1 uvcnq so n, 0 1 n ll The invention has been described in the light of a venturi device for a supercharged four-stroke internal combustion engine, but it is also applicable to other types of internal combustion engines, in which similar problems and conditions prevail. 71780; 2002-12 ~ 20

Claims (1)

1. 0 15 20: “% 5 524 515 12 I ~ | A device for exhaust gas recirculation (EGR) in an internal combustion engine (1), comprising an adjustable venturi device (9) for feeding exhaust gases into the engine inlet line (2) to, together with the engine inlet air is led to the engine (1), the venturi device (9) comprising a fixed venturi housing (8) and a movable venturi insert (10) and, for adjusting it, a pneumatic cylinder (21), the venturi insert (10) being adjustable in a first end position (10 ') where it is maximally inserted into the inlet line (2), and a second end position (10 "') where it is maximally removed from the inlet line (2), and wherein the pneumatic cylinder (21) is actuable in one direction of compressed air and in a second direction of a (first) return spring, characterized in that the pneumatic cylinder (21) is designed to also bring the vent insert (10), to a distinct intermediate position (10 ") between device according to claim 1, characterized in that the intermediate position (10 ") against corresponds to operation of the motor (1) in an operating case corresponding to 50-80% of the full power of the motor (1). Device according to claim 1, characterized in that the pneumatic cylinder (21) is designed to bring the venturi insert (10) to a further distinct intermediate position. Device according to one of Claims 1 to 3, characterized in that an EGR valve (6) is provided for shutting off the exhaust gas return to the engine (1). Device according to claim 1, characterized in that the cylinder (21) has a first air intake (18) which communicates with a 71780; 2002-12-20 10 l5 20, ~ -2,5 É'-3: 0 524 515 13 on -, u first chamber (16) comprising a first piston (14), the stroke of which is limited in axial direction, and a second air intake (19) which communicates with a second chamber (17) comprising a second piston (15), the stroke of which in axial direction is greater than the stroke of the first piston (14), the first piston (14) being arranged so that at pressurized air contact the second piston (15) and push this second piston (15) to a distinct intermediate position, corresponding to the distinct intermediate position (10 ") of the venturi insert (10), and wherein the second piston (15) is arranged to take a end position, corresponding to one of the end positions of the venturi insert (10 ', 10 "') under the action of compressed air by the second chamber (17). Device according to claim 5, characterized in that the first piston (14) and the first chamber (16) are annular. Device according to Claim 5 or 6, characterized in that the second air intake (19) extends inside the first chamber (16). Device according to claim 1, characterized by spring return means for being able to bring a piston movable in the cylinder against the action of spring return with a first spring constant to a distinct intermediate position during the action of compressed air at a first, lower, level, corresponding to the distinct intermediate position (10 ") of the venturi insert and in the action of compressed air on the cylinder at a second, higher level, being able to bring the piston against the action of spring return with a second spring constant to an end position corresponding to one of the end positions of the venturi insert (10 ', 10 "'). Device according to claim 8, characterized in that the spring return means also includes a second return spring 71780; 2002-12-20 10 15 20 10 ll 12 13. Device according to claim 8, .Q (1 ° 524 515 ¿'._ .: ¿.._ ¿14 (12), with a length less than the first return spring ( Device according to claim 9, characterized in that the two return springs (11, 12) are centered around the longitudinal axis of the pneumatic cylinder, 9 or 10, characterized in that the first level corresponds to an overpressure of about 1-2 bars, the The second level corresponds to an overpressure of about 5-8 bars. The internal combustion engine, characterized in that it comprises a device according to any one of claims 1 to 11. The process for exhaust gas recirculation (EGR) in an internal combustion engine (1) which comprises an adjustable venturi device. (9) for feeding exhaust gases into the engine inlet line (2) to be led together with the engine inlet air to the engine (1), the venturi device (9) comprising a fixed venturi housing (8) and a movable venturi insert (10) and, for setting this, a pneumatic cylinder (21), the venturi insert (10) being set in a first end position (10 ') then it is maximally inserted in the inlet line (2), or in a second end position (10 "') where it is maximally removed from the inlet line (2), and the pneumatic cylinder (21) is actuated in one direction of compressed air and in a second direction of a (first) return spring, characterized in that the pneumatic cylinder (21), if necessary, also brings the vent insert (10), to a distinct intermediate position (10 ") between said end positions. 71780; 2002-12-20 1! . . . . ... . ..,. , _ 52. .. -. . . ... ". '."' 2 «. . . . K. Ü. . . . . . A method according to claim 13, characterized in that the intermediate position (10 ") is set during operation of the engine (1) in an operating case corresponding to 50-80% of the full power of the engine (1). 71780; 2002- 12-20