EP2769065B1

EP2769065B1 - Exhaust manifold for exhaust gases from a multi cylinder combustion engine

Info

Publication number: EP2769065B1
Application number: EP12842530.3A
Authority: EP
Inventors: Dennis KONSTANZER
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2011-10-20
Filing date: 2012-10-10
Publication date: 2016-12-14
Anticipated expiration: 2032-10-10
Also published as: EP2769065A4; CN103958848A; EP2769065A1; SE539038C2; WO2013058700A1; BR112014009374A2; SE1150971A1

Description

BACKGROUND TO THE INVENTION AND PRIOR ART

The present invention relates to a manifold for receiving exhaust gases from a multi-cylinder combustion engine according to the preamble of claim 1. The invention relates also to a combustion engine provided with such a manifold.
Exhaust gases from multi-cylinder combustion engines are usually received in a manifold. A manifold comprises branch lines which receive exhaust gases from the engine's cylinders and a common line which receives the exhaust gases from the respective branch lines. When the exhaust valves of a cylinder open, the exhaust gases flow out initially into a branch line at a high pressure substantially related to their pressure in the cylinder just after the combustion stroke has ended. The pressure of the exhaust gases in the branch line during the remainder of the time when the exhaust valves are open will be lower and be substantially related to the work which the piston performs in pushing the exhaust gases into the branch line from the cylinder. The exhaust valves of a cylinder are normally open for the whole of the exhaust stroke, i.e. for a relatively large proportion of the work cycle of a four-stroke engine. In multi-cylinder combustion engines the opening times of the exhaust valves of the various cylinders usually overlap. In such situations, exhaust gases are led out into the manifold from two or more cylinders simultaneously.
Leading exhaust gases out from two or more cylinders simultaneously into a shared manifold is not uncomplicated. When the exhaust valves of the cylinder open, the exhaust gases are led out at high pressure from the cylinder into the connected branch line and the common line. If exhaust gases are at the same time led out from another cylinder into another branch line at a lower pressure, there is obvious risk that those at the higher pressure may make their way down into the branch line which is at the lower pressure. The pressure in this latter branch line will therefore rise, necessitating increased pumping work by the cylinder's piston to drive out the exhaust gases. The increased amount of pumping work results in increased fuel consumption of the engine. This disturbance to the exhaust flow in a manifold may be referred to as cross-leakage.
A known way of counteracting this disturbance is to provide the common line with constrictions close to the outlets into it from the branch lines, thereby raising the velocity of the exhaust gases and reducing their static pressure close to the outlets from the branch lines into the common line. The reduced static pressure of the exhaust gases makes it possible for exhaust gases to be led out at a lower pressure from a branch line into the common line. Providing the common line with constrictions does however have the disadvantage of increasing the flow losses of the exhaust gases in the common line.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a manifold for receiving exhaust gases from a combustion engine such that the risk of the type of exhaust flow disturbance called cross-leakage is substantially eliminated while at the same time the flow losses of the exhaust gases in the common line can be kept at a low level.
This object is achieved with the manifold of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. Using a guide element is a simple way of reducing the cross-section for the flow of exhaust gases in the common line close to the outlet aperture of the second branch line. The exhaust gases in the common line thus assume an increased velocity and a reduced static pressure close to the outlet aperture from the second branch line into the common line. This means that the risk of exhaust gases from the common line being led down into the second branch line is substantially eliminated even in situations where the exhaust valves of the first cylinder open when those of the second cylinder are already open. There is thus no need for the piston in the second cylinder to perform any extra pumping work in order to drive the exhaust gases out from the cylinder to the second branch line and the common line in such circumstances. The guide element comprises an edge portion where the contact of the exhaust gases with the guide element ceases. Relief vortices inevitably occur downstream of the edge portion. The guide element is therefore provided with a hole so that part of the exhaust gases can pass through to the leeside of the guide element. The negative pressure on the leeside of the guide element is thus reduced, with consequent reduction in the magnitude of the relief vortices and hence reduction of the losses of the exhaust gases in the common line when they flow past the guide element. The guide element may be provided with more than one hole.
According to an embodiment of the present invention, the guide element protrudes into the common line so as to cause a reduction of the order of 10-40% in the cross-section for the flow of exhaust gases. Such a reduction of flow cross-section may increase the velocity of the exhaust gases markedly and lower their static pressure to a level at which the risk of cross-leakage is substantially eliminated without causing too much resistance to their flow when they pass the guide element. The guide element is with advantage so positioned as to mainly reduce the flow cross-section for the exhaust gases on the side of the common line where the outlet aperture of the second branch line is situated. The guide element is with advantage positioned substantially immediately upstream of the outlet aperture into the common line with respect to the direction of exhaust flow in the common line. The exhaust gases in the common line will thus flow past the outlet aperture of the second branch line at a distance which is defined by how far the guide element protrudes into the common line. A further result is a region downstream of the guide element where the exhaust gases from the second branch line can be led into the common line. Such a guide element also tends to prevent exhaust gases from the second branch line from moving in an undesired direction in the common line.
According to another preferred embodiment of the present invention, the guide element comprises a first guide surface which is adapted to being encountered by part of the exhaust gases flowing in the common line and which has a slope such that it progressively reduces the cross-section for the flow of exhaust gases close to the second outlet aperture. This progressive reduction in the flow cross-section means that the flow losses of the exhaust gases in the flow-reducing region can be kept at a low level. Said hole may have a cross-section amounting to 5-15% of that of the first guide surface. With such a hole, a relatively small proportion of the exhaust gases reaching the guide element will pass through to its leeside but will in most cases be sufficient to reduce the exhaust vortices which occur downstream of the guide element. The exhaust flow through said hole also causes a shift of the exhaust vortices away from the guide element. An appropriate such shift will result in the vortices being at a location where they at least partly mask the outlet aperture of the second branch line, thus further reducing the risk of exhaust gases from the common line making their way down into the second branch line.
According to another preferred embodiment of the present invention, the guide element comprises a second guide surface which is adapted to guiding the exhaust gases when they are led into the common line from the second branch line and which has a slope substantially parallel with the direction of flow of the exhaust gases leaving the second branch line. The second branch line has with advantage a certain curvature close to its outlet aperture into the common line so that the exhaust gases leaving it are led in a direction which at least partly corresponds to their intended direction of flow in the common line. When the exhaust valves of the second cylinder open, the exhaust gases flow out from the second branch line into the common line at high velocity and the second guide surface of the guide element leads them into the common line in a desired direction. The second guide surface thus substantially prevents the exhaust gases from flowing in an incorrect direction in the common line and into a branch line situated upstream. In this case the second guide surface forms an angle with the extent of the hole so that substantially no exhaust gases from the second cylinder pass through the hole. The hole in the guide element thus does not tend to encourage any exhaust flow in incorrect directions in the common line.
According to another preferred embodiment of the present invention, the guide element has a substantially constant wall thickness, in which case the first and second guide surfaces will be substantially parallel. Such a guide element may with advantage have a relatively simple configuration. Its wall thickness may be thinner than that of the branch lines and the common line. It may take the form of a tubular portion of the second branch line which protrudes into the common line. During a process of manufacturing the manifold, this tubular portion may be inserted through an aperture in the common line to a position at which it protrudes into an appropriate section of the common line, followed by the branch line and the common line being connected together by welding or some other fastening method. Alternatively, the guide element may take the form of a separate unit fastened inside the common line by a suitable fastening method. Such a separate guide element may be provided with individually formed first and second guide surfaces.
According to another preferred embodiment of the present invention, the manifold comprises at least three branch lines leading exhaust gases from three cylinders to the common line. The more cylinders of the combustion engine are connected to a common line, the more difficult it becomes to prevent mutual overlap of the opening times of the exhaust valves of two cylinders. In the case of a manifold receiving exhaust gases from four cylinders it is substantially impossible to prevent mutual overlap of the opening times of the exhaust valves of the various cylinders.

BRIEF DESCRIPTION OF THE DRAWING

Preferred embodiments of the invention are described below by way of examples with reference to the attached drawings, in which

Fig. 1: depicts a manifold for receiving exhaust gases from a four-cylinder combustion engine,
Fig. 2: depicts a connecting region between a common line and a branch line of the manifold and
Fig. 3: is a sectional view of the common line in the plane A-A in Fig. 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 depicts schematically a combustion engine 1 with four cylinders 2a-d. The exhaust gases from the engine's cylinders are received in a manifold. The manifold comprises four branch lines 3a-d which each receive exhaust gases from one of the four cylinders. The manifold comprises a common line 4 which receives exhaust gases from the branch lines. The common line 4 leads into an exhaust line 5 which may lead the exhaust gases to a turbine of a turbo unit. The exhaust flow from the engine's respective cylinders 2a-d is controlled by at least one exhaust valve which is arranged to be movable between closed and open states. Each of the cylinders 2a-d are often provided with two exhaust valves to facilitate the exhaust flow from the cylinders.
When the exhaust valves open, an initial exhaust flow at high pressure is led out from the cylinder 2a-d to the common line 4 via the respective branch line 3a-d. For the remainder of the time when the exhaust valves are open, the exhaust gases are driven out at a lower pressure into the branch line 3a-d. This lower pressure is defined substantially by the movements of the piston in cylinder 2a-d when it pushes the exhaust gases out from the cylinder into the branch line. When a manifold receives exhaust gases from four cylinders 2a-d, it is substantially impossible to prevent mutual overlap of the opening times of the exhaust valves of the respective cylinders. The manifold will therefore receive exhaust gases from more than one cylinder in certain circumstances.
In situations where the exhaust valves of two cylinders are open at the same time, their respective exhaust flows may affect one another, particularly in cases where exhaust gases from two cylinders are led out into the manifold at markedly different pressures. This happens where the exhaust valves of one cylinder open when those of another cylinder are already open. In such situations the exhaust gases which are at the higher pressure will flow down into the branch line which is leading out exhaust gases at the lower pressure. The pressure in the branch line will therefore rise, necessitating an increased amount of pumping work by the piston of the respective cylinder in order to pump out the exhaust gases. Such increased pumping work will lead to higher fuel consumption of the engine. To prevent this disturbance of the exhaust flow in the manifold, which may be referred to as cross-leakage, a guide element 7 is provided in each of the connecting regions where the branch lines 3b-d have outlet apertures 3b₁-3d₁ which lead exhaust gases out into the common line 4.
Fig. 2 depicts in more detail the connecting region where the branch line 3c leads exhaust gases out into the common line 4. The guide element 7 is situated in the common line immediately upstream of the branch line's outlet aperture 3c₁ into the common line with respect to the intended direction of flow of the exhaust gases in the common line. The guide element has a clear edge portion 7d which protrudes a certain distance into the common line so as to reduce the cross-section for the flow of exhaust gases in the common line close to the connecting region. The resulting reduction in the flow cross-section of the common line may be of the order of 10-40%. The guide element may for example reduce the flow cross-section by 30%. The guide element is so positioned as to mainly reduce the cross-section for the flow of exhaust gases on the side of the common line where the branch line has its outlet aperture 3c₁. The guide element has a first guide surface 7a adapted to being encountered by the exhaust gases flowing in the common line. This first guide surface is at an angle to the direction of flow of the exhaust gases in the common line which subjects them to a relatively gentle change of direction when they encounter the guide element. The guide element thus reduces the flow cross-section in the connecting region between the common line and the branch line. The exhaust gases in the common line thus assume an increased flow velocity in the connecting region and a reduced static pressure which diminishes their tendency to flow down into the branch line.
The guide element 7 has a second guide surface 7b intended to lead the exhaust gases into the common line 4 from the branch line 3c. The branch line has a curvature upstream of its outlet aperture 3c₁ so that the exhaust gases led through the aperture assume a direction of flow at least partly corresponding to the main direction of flow of the exhaust gases in the common line. This second guide surface substantially maintains continuity of the direction of flow of the exhaust gases for a certain distance into the common line. The guide element takes the form of a relatively thin-walled element with a substantially constant wall thickness. The first guide surface 7a and the second guide surface 7b are therefore parallel. In this case the guide element takes the form of an end portion of a pipe which constitutes the branch line 3c. It may alternatively take the form of a separate unit fastened in an appropriate way in the connecting region between the common line and the branch line.
The guide element 7 has running through it a hole 7c, the size of which is such that a small proportion of the exhaust gases flowing through the common line passes through said hole. Fig. 3 is a cross-sectional view in the plane A-A in Fig. 2. The hole is in this case circular and positioned substantially centrally on the first guide surface 7a. The cross-section of the hole amounts to 5-15%, preferably 10%, of that of the first guide surface. The hole serves as a short flow duct with in this case an extent substantially parallel with the main direction of flow of the exhaust gases in the common line. Alternatively it may have an extent which forms substantially a right angle with the first guide surface 7a and the second guide surface 7b.
In situations where the exhaust valves of either of the cylinders 2a, 2b open when those of the cylinder 2c are already open, the result is a momentary exhaust flow into the manifold from two cylinders. The flow from the cylinders 2a, 2b is led out at high pressure into the common line 4 at a location upstream of the branch line 3c. When the exhaust gases in the common line reach the connecting region with the branch line, part of the exhaust flow encounters the first guide surface 7a which reduces the cross-section for their flow, with the result that they assume an increased velocity and a reduced static pressure in the connecting region. When the exhaust gases leave the guide surface 7 an exhaust vortex 8 forms in a region immediately downstream of the edge portion 7d. A small proportion of the exhaust flow in the common line passes through the hole 7c in the guide element. This exhaust flow through the hole raises the pressure on the leeside of the guide element, thereby reducing the magnitude of the exhaust vortex and hence the flow losses of the exhaust gases in the common line. At the same time, the exhaust flow through the hole shifts the exhaust vortex 8 a certain distance downstream away from the guide element to a location substantially above the branch line's outlet aperture 3c₁ into the common line and particularly above a downstream portion of the outlet aperture where there is greatest risk that exhaust gases from the common line might make their way down into the branch line. When the exhaust vortex is at this location it thus very effectively prevents the exhaust flow in the common line from being led down into the branch line.
If conversely the exhaust valves of the cylinder 2c open at a time when those of either of the upstream cylinders 2a, b are open, exhaust gases at high pressure will flow out from the cylinder 2c and reach the common line 4 via the branch line 3c. The guide element's second guide surface 7c will lead the exhaust gases in the common line in the intended direction in the common line, preventing them from flowing in an incorrect direction in the common line.
Even if the exhaust valves of either of the cylinders 2a, 2b are already open when those of the cylinder 2c open, the guide element thus prevents the exhaust gases from the cylinder 2c from reaching the upstream branch lines 3a, 3b. As the exhaust gases flow along the second guide surface 7b at high velocity in a direction which is clearly different from the direction of flow through the hole 7c, there will in this case be substantially no exhaust flow through the hole.
The invention is in no way restricted to the embodiment described above but may be varied freely within the scopes of the claims. The shape of the guide element may for example be varied, as also the number of holes in it and the shape and position of the hole. The number of cylinders which connect to a common line via branch lines may also vary, and in its simplest form the engine may have only two cylinders which connect to a common line. V8 engines for example usually have two common lines each which connect to the respective bank of cylinders on their respective side of the engine. In such a configuration it is appropriate for each common line to be configured as in the example described above.

Claims

A manifold for receiving exhaust gases from a multi-cylinder combustion engine (1), such that the manifold comprises a common line (4), a first branch line (3a-c) adapted to receiving exhaust gases from a first cylinder (2a-c) and to leading them into the common line (4) via a first outlet aperture (3a₁-3c₁), and at least one second branch line (3b-d) adapted to receiving exhaust gases from a second cylinder (2b-d) and to leading them into the common line (4) via a second outlet aperture (3b₁-3d₁) situated downstream of the first outlet aperture with respect to the intended direction of flow of the exhaust gases in the common line (4), and the common line (4) has in it close to the second outlet aperture (3b₁-3d₁) a reduced cross-section for the flow of exhaust gases, wherein the manifold is provided with a guide element (7) which comprises a first guide surface (7a) with a clear edge portion (7d) which protrudes into the common line (4), thereby reducing the cross-section for the flow of exhaust gases close to the second outlet aperture (3b₁-3d₁) so that part of the exhaust gases encounters the guide surface (7a) and a remaining portion of them is led past the guide element (7) without encountering the guide surface (7a), and that the guide element (7) is situated immediately upstream of the branch line's outlet aperture (3c₁) into the common line (4) with respect to the intended direction of flow of the exhaust gases in the common line, characterised in that the guide element (7) has running through it at least one hole (7c), the size of which is such that part of the exhaust gases in the common line (4) which encounter the guide surface (7a) passes through said hole (7c).
A manifold according to claim 1, characterised in that the first guide surface (7a) protrudes into the common line, resulting in a reduction of the order of 10-40% in the cross-section for the flow of exhaust gases in the common line.
A manifold according to claim 1 or 2, characterised in that the guide element (7) is so positioned as to mainly reduce the cross-section for the flow of exhaust gases on the side of the common line (4) where the second outlet aperture (3b₁-3d₁) is situated.
A manifold according to any one of the foregoing claims, characterised in that the first guide surface (7a) has a slope such that in the direction of flow it progressively reduces the cross-section for the flow of exhaust gases close to the second outlet aperture (3b₁-3d₁).
A manifold according to any one of the foregoing claims, characterised in that said hole (7c) has a cross-section amounting to 5-15% of that of the first guide surface (7a).
A manifold according to any one of the foregoing claims, characterised in that the guide element (7) comprises a second guide surface (7b) which is adapted to directing the exhaust gases led into the common line (4) from the second outlet aperture (3b₁-3d₁) and which has a slope substantially parallel with the direction of flow of the exhaust gases leaving the second branch line (3b-3d).
A manifold according to any one of the foregoing claims, characterised in that the guide element (7) has a substantially constant wall thickness.
A manifold according to any one of the foregoing claims, characterised in that the guide element (7) takes the form of a tubular portion of the second branch line (3b-d) which protrudes into the common line (4).
A manifold according to any one of the foregoing claims, characterised in that the guide element (7) takes the form of a separate unit fastened inside the common line (4).
A manifold according to any one of the foregoing claims, characterised in that it comprises at least three branch lines which lead exhaust gases from three cylinders to the common line (4).
A combustion engine characterised by being provided with a manifold according to any one of the foregoing claims.