WO2013093541A1

WO2013093541A1 - Cylinder head for engine

Info

Publication number: WO2013093541A1
Application number: PCT/IB2011/003247
Authority: WO
Inventors: Frederi Imbert; Claes Kuylenstierna
Original assignee: Renault Trucks; Volvo Lastvagnar Ab
Priority date: 2011-12-22
Filing date: 2011-12-22
Publication date: 2013-06-27

Abstract

The invention relates to a cylinder head (1) suited to be fitted above a cylinder block of a combustion engine having at least one cylinder, provided with at least one intake port and at least one exhaust port (12) facing the at least one cylinder and provided with corresponding intake and exhaust conduits (10) allowing gases to respectively enter and escape in and out of the cylinder, said cylinder head having a valve seat at said intake and exhaust ports comprising a sealing surface (23) whereon a movable valve (40) can rest during a fraction the engine cycle, characterized in that said cylinder head further has condensate collecting means provided along the flow of gases and capable of collecting and retaining condensate substantially away from the sealing surface.

Description

CYLINDER HEAD FOR ENGINE

Field of the invention

The present invention concerns a cylinder head for an internal combustion engine, a valve seat insert for a cylinder head and a vehicle equipped with such cylinder head.

Technological background

In a conventional internal combustion engine, a cylinder head sits above the engine block. At least one intake valve and one exhaust valve are positioned within the engine cylinder head and above the engine cylinder. The cylinder head is also provided with corresponding intake and exhaust conduits through which flow respectively the intake gases and the exhaust gases generated by the combustion process.

The temperature in the intake and exhaust conduits may change upon starting and stopping of the engine, but also during operation of the engine.

During cooling down phases, water can condense on the side wall of the intake or exhaust conduits provided in the cylinder head. This is specially the case in cold climate environments, most notably at the time when the engine is stopped.

Condensation water and other components, especially chemical residues from combustion, can mix. This can promote the production of a corrosive liquid in the intake or exhaust conduit which may contain corrosive substances such as sulphuric acid when sulphur residues from the combustion process mix with condensation water.

Due to the common general engine architecture and positioning where the exhaust conduit is positioned substantially above the cylinder head, the said corrosive liquid can flow along the internal side wall of the cylinder head intake or exhaust conduit towards the intake or exhaust valve and can thus flow between the valve and the valve seat. As a result, the valve seat and/or the valve can get corroded by this liquid, especially the sealing surface of the seat against which the valve is supposed to contact in a substantially fluid tight manner. Over time, the corrosion of the valve seat can be so severe that it may cause valve leakage. Valve leakage will then compromise the engine compression ratio and therefore the engine efficiency, performance, exhaust emissions, and ultimately engine operation may be altered. In many engine designs, each valve seat is formed on a valve seat insert which is fitted on the cylinder head at the corresponding intake or exhaust port.

Conventional technologies tackle the problem of corrosion by making valve seat inserts of anticorrosion material, such as a Nickel based alloy or a Cobalt based alloy.

However, these technologies substantially increase the cost of the valve seat inserts. Besides, anticorrosion materials prove to have poor valve recession performance.

Thus, there is room for improvement in dealing with corrosion produced by engine gases condensate.

Summary In this technical context, it is an object of the present invention to provide an improved cylinder head which can overcome the aforementioned drawbacks and prevent a harmful corrosion to the valve seat.

In a general definition, the invention proposes a cylinder head suited to be fitted above a cylinder block of a combustion engine having at least one cylinder, provided with at least one intake port and at least one exhaust port facing the at least one cylinder and provided with corresponding intake and exhaust conduits allowing gases to respectively enter and escape in and out of the cylinder, said cylinder head having a valve seat at said intake and exhaust ports comprising a sealing surface whereon a movable valve can rest during a fraction the engine cycle, said cylinder head further having condensate collecting means provided along the flow of gases capable of collecting and retaining condensate substantially away from the sealing surface.

Accordingly, in the cylinder head arrangement according to the invention, any corrosive liquid (such as water and sulphuric acid) formed in the intake and/or exhaust conduit is prevented from reaching the internal surface of the valve seat which is critical in terms of engine operation. The cylinder head of the invention makes it possible to channel corrosive liquid in a non-critical area of the cylinder head where the corrosive effect is not detrimental to the engine operation.

According to an embodiment of the invention, the condensate collecting means comprises a collecting cavity located above the valve seat sealing surface.

In this aspect of the invention, the collecting cavity prevents corrosive liquid to contact the valve seat sealing surface. The collecting cavity makes it possible to store the corrosive liquid in a limited area where corrosion is not detrimental to engine operation.

Preferably, the collecting cavity exhibits a concavity turned upwards so as to be able to retain a liquid against gravity.

In a preferred embodiment, the collecting cavity extends annularly around the corresponding intake or exhaust conduit. This proves a significant advantage, especially in the cases where the exhaust conduit is substantially vertical, insofar as corrosive liquid can be substantially entirely prevented from flowing to the sealing surface of the valve seat. Nevertheless, especially if the orientation of the exhaust conduit is not vertical but is inclined, it may be sufficient to provide a cavity extending on only part of the circumference of the conduit where condensate is prone to be channeled under the effect of gravity.

In an implementation of the invention, the collecting cavity is formed in part by an insert and in part by the exhaust conduit.

In another implementation, the collecting cavity is formed in an insert.

Such insert may be a valve seat insert fitted on the cylinder head and on which is formed the sealing surface.

In still another implementation, it is formed in a side wall of the intake and/or exhaust conduit. For example, the intake and/or exhaust conduit is provided with an annular recess shaped to form an annular collecting cavity.

In all cases, an upwardly protruding rib may be provided to form a radially inner edge of the annular collecting cavity. When said rib is formed on an insert, especially on a valve seat insert, it is preferably radially spaced apart from the side wall of the corresponding intake or exhaust conduit. Thus, the rib forms an obstacle preventing corrosive liquid from flowing down the conduit and consequently from reaching the valve seat sealing surface. In an implementation of the invention, the annular collecting cavity is formed between a first annular rib and a second annular rib projecting upwardly and concentrically from the insert. The annular cavity which scoops corrosive liquid flowing down the intake or exhaust conduit is thus entirely formed on the insert.

In an embodiment of the invention, the annular collecting cavity comprises an inner surface coated with a corrosion resistant material, such as a nickel base material or a cobalt base material. The resistant corrosion material which can be expensive is thus limited to a small area of the cylinder head.

It is also envisaged to fit the annular collecting cavity with a ring made of a corrosion resistant material, such as nickel based material or a cobalt based material.

In an aspect of the invention, the exhaust conduit comprises a flared shape portion positioned above the collecting cavity.

The invention also concerns a valve seat insert, wherein the valve seat insert is of annular shape around a central vertical axis and has a downwardly facing sealing surface whereon a movable valve can rest, characterized in that the valve seat insert has an upwardly protruding annular rib which is designed to form a radially inner edge of an annular cavity exhibiting a concavity turned upwards.

Furthermore, the valve seat insert may have a first annular rib and a second annular rib projecting upwardly and concentrically for forming an annular cavity exhibiting a concavity turned upwards.

The surface of the valve seat insert forming the cavity may be coated with a corrosion resistant material, and/or may be lined with a ring made of a corrosion resistant material.

The invention also concerns a combustion engine installation comprising a cylinder block and a cylinder head installed so that the cylinder head is fitted above the cylinder block, wherein the cylinder head and/or the valve seat insert is conform to any preceding feature.

Such installation can be a fixed installation or can be provided in a vehicle or in a construction equipment machine.

These and other advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non-limiting examples, embodiments of a cylinder head according to the invention.

Brief description of the drawings

The following detailed description of embodiments of the invention is better understood when read in conjunction with the appended drawings. However, the invention is not limited to these specific embodiments disclosed. In the drawings:

Figure 1 is a cross section of a cylinder head according to an embodiment of the invention,

Figure 2 is an enlarged view of a detail of figure 1 , showing a valve seat insert of a cylinder head according to an embodiment of the invention,

Figure 3 is a perspective view of a valve seat insert of a cylinder head according to an embodiment of the invention,

Figures 4, 5, 6 and 7 are cross sections of a part of a cylinder head according to further embodiments of the invention.

Detailed description of the invention

An internal combustion engine, especially of the four strokes reciprocating piston type, usually comprises a cylinder block, in which are arranged one or several cylinders for accommodating each a reciprocating piston. Such engines may have many different configurations, such as:

- in line, where the cylinders are arranged in parallel ;

- V-type, comprising two rows of parallel cylinders, the two cylinder axis directions forming a V around a common crankshaft axis ;

- opposed-piston or boxer type, having set of opposed pistons, etc...

An internal combustion engine can be used in a variety of installations, for example in a stationary installation, in an in-vehicle installation, in an in-machine installation, etc...

In a stationary installation, the internal combustion engine will have a fixed orientation with respect to gravity. In an in-vehicle or in-machine installation, the engine will have a fixed orientation with respect to the vehicle or to the machine. Of course, the orientation of the vehicle with respect to gravity will impact the orientation of the engine with respect to gravity, but it can nevertheless be assumed that in most cases, it can be considered that the vehicle or machine is mainly standing on a substantially horizontal surface.

Depending on the engine type and on its installation, the axis of the cylinder can therefore have very different orientations with respect to gravity.

As this is illustrated in figure 1 , a cylinder head 1 for a combustion engine can be a cast element which comprises intake conduits that feed air, and in some cases fuel, to the cylinder, and exhaust conduits that allow the exhaust gases to escape. The cylinder head is also a place to mount the valves, spark plugs, and fuel injectors. The cylinder head is fitted above the cylinders on top of the cylinder block (not shown) and thus closes the top of the cylinder, forming the combustion chamber. The opening and closing of the cylinder intake and exhaust ports are therefore controlled by the positions of the valves, which are most commonly reciprocating valves sliding in the cylinder head along a valve axis A40. The valve axis can be parallel to the cylinder axis, but can also be inclined with respect to that axis. All valves for a same cylinder do not necessarily have the same inclination with respect to the cylinder axis.

In the example shown and described, the valve axis will be considered to be substantially vertical, whatever its inclination with respect to the cylinder axis. Such vertical orientation of the valve axis can occur in an engine installation where at least one cylinder axis is substantially vertical and where at least one valve axis is substantially parallel to the cylinder axis. It can occur also in an installation where the engine cylinder is inclined with respect to the vertical but where the valve axis is inclined by a mirror angle with respect to the cylinder axis. The notions used hereinafter of top and bottom therefore relate to such and engine installation.

The invention can be applied to both the intake and exhaust conduits and ports of an engine cylinder. In the example described hereinafter, the application to an exhaust port will be described.

As it can be seen on Fig. 1 , the cylinder head 1 includes an exhaust conduit 10 which leads to an exhaust port 12 formed in a bottom surface of the cylinder head which faces the cylinder and which forms the cylinder roof. In the vicinity of the exhaust port 12, the exhaust conduit 10 can be considered to extend along a direction which is substantially parallel to the valve axis. In the vicinity of exhaust port 12, the exhaust conduit 10 can be provided with a recess in its side wall 11 for accommodating a valve seat insert, said recess being delimited by an annular shoulder surface 13 which extends radially outwardly from the side wall in a plane perpendicular to the valve axis and which faces downwards, and by a substantially cylindrical surface 14 which extends downwardly from the shoulder surface 13, preferably substantially parallel to the valve axis, as visible on figure 2.

The cylinder head is also suitably provided with cooling conduits 15 and valve guides 16, said valve guides being oriented along the corresponding valve axis.

A valve seat insert 20 having an annular shape is fitted in the exhaust port 12 and is provided with a sealing surface whereon an exhaust valve 40 (not shown on Fig. 1 or Fig. 2) can sit during most of the intake, compression and combustion strokes of the engine. The valve seat insert 20 can be made of a suitable iron-based material.

The valve seat insert 20 comprises an upper annular surface 21 , an external surface 22, preferably a cylindrical surface facing outwardly, and an internal sealing surface 23. The internal sealing surface 23 can have a substantially frustoconical, downwardly facing, profile to ensure a fluid-tight contact with an exhaust valve. The sealing surface 23 is preferably an annular portion of a radially internal surface which extends from top to bottom of the seat insert. Preferably, the radially internal surface is parallel or nearly parallel to the valve axis at its top portion and is flared so that its diameter with respect to the valve axis progressively widens, and so that its orientation becomes more inclined with respect to the valve axis. In this embodiment of the invention, the upper surface 21 includes an annular rib 24 which projects upwardly with respect to the upper surface 21. As illustrated on Figs. 1 to 3, the annular rib 24 is preferably located on a radial inner edge of the annular upper surface and is preferably substantially flush with the top part of the valve seat insert radially internal surface which bears the sealing surface 23.

The upper surface 21 of the valve seat insert is intended to be in contact with the shoulder surface 13 provided in the exhaust port 12. The valve seat insert 20 can be suitably press fitted into the exhaust port 12.

As can be seen on figure 2, the upper surface 21 of the valve seat insert 20 can partially (and not entirely) abut against the shoulder surface 13, i.e. part of the upper surface may remain uncovered by the shoulder surface 13. A radial gap is indeed advantageously provided between the side wall of the exhaust conduit 10 and the annular rib 24, thereby creating a collecting cavity 26, which, in this example, is formed in part by valve seat insert 20 and in part by the side wall of the exhaust conduit.

In operation, corrosive liquid can appear in the form of droplets 30 on the surface of the exhaust conduit 10.

This phenomenon can be promoted by warm-up and/or cooling down phases of the engine where water together with combustion residues may condense on the exhaust conduit 10.

As droplets 30 of corrosive liquid are produced on the exhaust conduit 10, the said droplets 30 of corrosive liquid may tend to flow along the exhaust conduit 10 side wall, towards the exhaust port 12, depending on the orientation of the side wall with respect to gravity.

Under the effect of gravity, the droplets 30 of corrosive liquid flow into the collecting cavity 26 which is created between the exhaust conduit 10 and the valve seat insert 20. The corrosive liquid, or at least a substantial part of it, is channelled into the collecting cavity 26 and thus does not flow towards the radially internal surface of the valve insert which bears the sealing surface 23. Accordingly, the sealing surface 23 of the valve insert, which is critical for valve tightness, is substantially preserved from a detrimental contact with the droplets 30 of corrosive liquid.

The droplets 30 of corrosive liquid are diverted and are retained into a non-sensitive area of the cylinder head 1 while the critical area of the valve seat sealing surface 23 remains substantially protected and thus substantially unaffected by the corrosive liquid. Of course, it could be that, under certain circumstances, some droplets are formed directly on the valve or on the radially internal surface of the valve seat, or that some droplets do not flow along the side wall to be collected in the cavity 26 but drip directly on the valve seat, or that an excess amount of condensate is collected in the cavity, so that it may over-flow. In such cases, a certain amount of corrosive condensate may flow to valve / seat interface. Nevertheless, it is expected that such circumstances should be non-frequent and/or limited in the amount of condensate. For example, the cavity should be properly dimensioned to retain a major proportion of the condensate formed during a cooling down phase of the engine and which would tend to flow towards the valve / seat interface. The suitable retaining capacity for the cavity may vary depending on the engine type, the engine displacement, the cylinder head conduits geometry, the engine installation, and depending on whether the conduit is an intake or an exhaust conduit. It can range for example from 50 to 1000 cubic millimetres for the exhaust conduit of a 7 to 16 litres displacement diesel engine.

It can further be noticed that the side wall 11 can be shaped to guide the condensate droplets into the collecting cavity 26. For instance, the side wall 11 can have a flared shaped portion 18. The internal side wall 11 can widen just above the collecting cavity 26. Instead of flowing directly on the valve seat insert 20, the droplets 30 of corrosive liquid thus flow along the internal side wall 11 into the collecting cavity 26.

As corrosive liquid is captured in the collecting cavity 26, at least the upper surface 21 of the valve seat insert 20 can be provided with suitable enhanced corrosion resistive properties. The upper surface 21 can thus have an anti-corrosion coating or can be fitted with a ring made of an anti-corrosion material. The potentially expensive corrosion resistant material is thus limited to a relatively small area, for example only the upper surface of the valve seat insert 20.

In an alternative embodiment illustrated in figure 4, the collecting cavity 26 is fully integrated to the valve seat insert 20. In this embodiment, the valve seat insert 20 comprises a first annular rib 24 and a second annular rib 25. The first annular rib 24 and the second annular rib 25 protrude upwardly from the upper surface 21. The first annular rib 24 can be flush with the top portion of radially internal surface of the seat insert. They are distant from each other and can be concentric. The collecting cavity 26 is thus formed between the annular ribs 24 and 25.

In an alternative further embodiment illustrated in figure 5, the collecting cavity 26 can be fully integrated into the conduit 10. In this embodiment, the side wall of the exhaust conduit 10 can be shaped to include a collecting cavity 26. A protruding rib 28 can form the radially inner edge of the collecting cavity 26.

In a further embodiment shown on figure 6, the cavity 26 is formed in part by the side wall 1 of the exhaust conduit, and in part by a further insert 50 which is distinct from the valve seat insert 20 and which is affixed on the cylinder head. In the shown example, the further insert 50 is installed between the valve seat insert 20 and the shoulder surface 13, and it exhibits an upwardly extending annular rib 24 at its radial inner edge. In this example, it is as if the seat insert of Figure 1 was in two parts, the top part forming the cavity 26 being the further insert 50. Such a further insert could be used in the absence of a valve seat insert. It could also be located more upwards in the exhaust conduit, not being in contact with a valve seat insert. Also, in a further embodiment, the cavity 26 could be integrally formed in such a further insert distinct from the valve seat insert.

On figure 7 is shown a further embodiment of the invention. In this embodiment, the engine installation is such that the valve 40 has an axis A40 which is inclined with respect to the vertical direction of gravity, by an angle a. Here the angle a is such that it is unnecessary to have a cavity extending all around the axis of the valve. It is sufficient to have a cavity on the lowermost side of the exhaust conduit. In this example, the cavity is here formed thanks to the provision of a recess, or flared portion 18, in the side wall 1 1 , but on only one side of the conduit 10, just above the valve seat insert 20. Thereby, a portion of the upper surface of the valve sear insert 20 is uncovered and forms, in part, the cavity 26, but only on one side of the conduit. On the side of the conduit with respect to axis A40, the radial inner edge of the valve seat insert can be flush with the inner wall of the conduit 10. Moreover, it can be seen that, in this example, the upper surface 21 of the seat insert 20 does not exhibit an upwardly protruding rib as in the other examples, as the inclination of the valve axis, and the corresponding inclination of the valve seat insert 20, allows the radial inner edge of the valve seat insert to be located above the lowest point of the cavity 26, such that a cavity with an upwardly turned concavity is nevertheless formed despite the absence of a rib.

The cylinder head 1 can be provided, in the area delimited by the collecting cavity 26, with enhanced corrosion resistive properties. The collecting cavity 26 can be provided with a coating of corrosion resistant material or can be fitted with a ring of corrosion resistant material as shown by element 27 of Figure 1.

In operation, in an exhaust conduit 10 for instance, during an engine warm-up or cooling phase, water may condense on the side wall 11 of the exhaust conduit. Water droplets may be mixed with sulphur residues from the combustion process and may form sulphuric acid. Due to the engine installation, i.e. its orientation with respect to gravity, some of this sulphuric acid may tend to flow along the side wall 11 towards the valve seat insert 20. This corrosive liquid is captured by the collecting cavity 26 located on the liquid's route, thus preventing it from reaching the internal surface 23 of the valve seat insert 20. Accordingly, thanks to a cylinder head 1 according to the invention, the corrosion of the fluid tight surface, located between the valve seat insert 20 and the valve 40 is substantially limited, without excessive costs.

The invention is not restricted to the embodiments described above by way of non-limiting examples, but on the contrary it encompasses all embodiments thereof. It can further be noticed that the embodiments above described can be implemented in combination. Thus the cylinder head of the invention can include a collecting cavity as illustrated on Figure 1 with a collecting cavity as described on Figure 5 for a combined corrosion liquid collecting effect.

Claims

1. Cylinder head (1) suited to be fitted above a cylinder block of a combustion engine having at least one cylinder, provided with at least one intake port and at least one exhaust port (12) facing the at least one cylinder and provided with corresponding intake and exhaust conduits (10) allowing gases to respectively enter and escape in and out of the cylinder, said cylinder head having a valve seat at said intake and exhaust ports comprising a sealing surface (23) whereon a movable valve (40) can rest during a fraction the engine cycle, characterized in that said cylinder head further has condensate collecting means provided along the flow of gases and capable of collecting and retaining condensate substantially away from the sealing surface.

2. The cylinder head (1) according to claim 1 , characterized in that the condensate collecting means comprises a collecting cavity (26) located above the valve seat sealing surface (23).

3. The cylinder head (1) according to claim 2, characterized in that the collecting cavity (26) exhibits a concavity turned upwards so as to be able to retain a liquid against gravity.

4. The cylinder head (1) according to any of claims 2 or 3, characterized in that the collecting cavity (26) is formed in part by an insert (20) and in part by the exhaust conduit (10).

5. The cylinder heard (1) according to any of claims 2 or 3, characterized in that the collecting cavity (26) is formed in an insert (20)

6. The cylinder heard (1) according to any of claims 4 or 5, characterized in that the insert is a valve seat insert (20) fitted on the cylinder head and on which is formed the valve seat sealing surface (23).

7. The cylinder head (1) according to any of claims 2 or 3, characterized in that the collecting cavity (26) is formed in a side wall of the intake and/or exhaust conduit (10).

8. The cylinder head (1) according to of claim 2 to 7, characterized in that the collecting cavity (26) extends annularly around the intake and/or exhaust conduit (10).

9. The cylinder head (1) according to claim 8, characterized in that an upwardly protruding rib (24, 28) forms a radially inner edge of the annular collecting cavity (26).

10. The cylinder head according to claims 8 and 5 in combination, characterized in that the annular collecting cavity (26) is formed between a first annular rib (24) and a second annular rib (25) projecting upwardly and concentrically from the insert.

11. The cylinder head according to of claims 2 to 10, characterized in that the collecting cavity (26) comprises an inner surface coated with a corrosion resistant material.

12. The cylinder head (1) according to one of claims 2 to 10, characterized in that the collecting cavity (26) is lined with a ring (27) made of a corrosion resistant material.

13. The cylinder head (1) according to one of claims 2 to 12, characterized in that the intake and/or exhaust conduit (11) comprises a flared shape portion (18) positioned above the collecting cavity (26).

14. The cylinder head (1) according to any preceding claim in combination with claims 7 and 8, characterized in that the intake and/or exhaust conduit (11) is provided with an annular recess shaped to form the annular collecting cavity (26).

15. Valve seat insert, wherein the valve seat insert is of annular shape around a central vertical axis and has a downwardly facing sealing surface whereon a movable valve can rest, characterized in that the valve seat insert has an upwardly protruding annular rib which is designed to form a radially inner edge of an annular cavity exhibiting a concavity turned upwards.

16. Valve seat insert according to claim 15, characterized in that the valve seat insert has a first annular rib and a second annular rib projecting upwardly and concentrically for forming an annular cavity exhibiting a concavity turned upwards.

17. Valve seat insert according to claim 15 or 16, characterized in that the surface of the valve seat insert forming the cavity is coated with a corrosion resistant material.

18 Valve seat insert according to claim 15 or 16, characterized in that the cavity is lined with a ring (27) made of a corrosion resistant material.

19. Combustion engine installation comprising a cylinder block and a cylinder head installed so that the cylinder head is fitted above the cylinder block, characterized in that the cylinder head and/or the valve seat insert is conform to any preceding claim.