CN101749141A - Cylinder head for a self-igniting internal combustion engine - Google Patents

Abstract

The invention relates to a cylinder head for a self-igniting internal combustion engine, in particular a cylinder head (10) with at least one exhaust passage (12) which can be closed by an exhaust valve (30) and comprising a cylinder head with at least A cooling air channel (41, 42) for loading the cooling air channel assembly of the exhaust valve with cool air. The cooling air ducts of the cooling air duct arrangement in the cylinder head are substantially linear and/or have a substantially constant or continuously increasing cross section.

Description

Cylinder heads for self-igniting internal combustion engines

technical field

The invention relates to a cylinder head (Zylinderkopf) according to the preamble of claim 1, in particular for a self-ignition (selbstzuendende) internal combustion engine, which has at least one exhaust gas channel (Auslasskanal), which can be Closed by an exhaust valve (Auslassventil); and with a cooling air channel assembly (Kuehlluftkanalanordnung) with at least one cooling air channel (Kuehlluftkanal) for use of cold air or other cooling gases (Kuehlgas) Loading of the exhaust valve (Beaufschlagung).

Background technique

The exhaust gases produced during combustion in internal combustion engines can reach very high temperatures. The exhaust gases flowing around the exhaust valves of such internal combustion engines are also a corrosive atmosphere, so there is a risk of thermal corrosion on the exhaust valves. Corroded valves can subsequently cause engine damage.

In order to avoid this effect, the engine is often operated at a lower output than the maximum possible engine output. In order to avoid high exhaust valve temperatures, it is also known to cool the exhaust valve by means of a generally liquid cooling medium circulating in the interior of the valve. However, this solution is relatively expensive. As another possibility for cooling at least the seat region of the exhaust valve, internal cooling of the valve seat is known. In this variant, however, the cooling effect on the valve cone is relatively insignificant.

Patent document DE 524 453 describes a valve cooling for an internal combustion engine by means of a gas jet blown against the side of the valve cone facing away from the combustion chamber. In this case, the device for supplying cooling gas has an annular space adjacent to and coaxially to the valve. The annular space includes injection openings distributed over its circumference and directed towards the valve cone. In this case, the annular space can be located within the cylinder head or in a device arranged in the cylinder head.

Patent application document DE 34 25 301 shows an air-cooled insert (Einsatz), which includes a valve seat. An annular space is again arranged coaxially to the valve on the outer periphery of the insert. The insert also has distributed injection holes on the inner circumference, which act on the valve cone with cooling air from the annular space.

Such known assemblies for cooling the side of the valve cone facing away from the combustion chamber always have collecting chambers or branches in the cylinder head. On the one hand, this results in a large surface area for the air supply system, so that the cooling air is already heated through the cylinder head housing. On the other hand, there are air turbulences, in particular backflows, which likewise lead to an increased heating of the cooling air before the valve surfaces are acted upon. The cooling effect achieved is thereby impaired.

Contents of the invention

Proceeding from the above-mentioned prior art, the object of the present invention is to provide a cylinder head for use, which has a cooling air module with a simple design, which avoids the disadvantages of the prior art and is used for Reduce the temperature of the exhaust valve.

To achieve this object, the cylinder head according to the preamble of claim 1 is improved by the features of its characteristic parts. Advantageous refinements are the subject matter of the subclaims.

The cylinder head according to the invention has at least one exhaust duct, which can be closed by an exhaust valve. The cylinder head also has a cooling air duct arrangement with at least one cooling air duct for acting on the exhaust valve with cooling gas, in particular cold air.

According to a first embodiment of the invention, the cooling air passages of the cooling air passage assembly are configured substantially linear in the cylinder head. As a result, flow losses due to deflections of the cooling air and frictional losses, which increase proportionally to the length of the cooling air channel to flow through, are minimized. The linear configuration of the cooling air channel also has the advantage of a direct supply of cooling air to the outlet valve. As a result, the heat input to the cooling gas when the cooling gas flows past the hot cylinder head surface is reduced to a minimum as much as possible.

A change, in particular a sudden change, in the cross-section in the flow-through channel can lead to turbulence and/or to a blockage of the flowing medium. In this design, in the present case, the residence time and the contact between the cooling air and the cylinder head surface would increase, which would likewise lead to a heating of the cooling gas and thus a reduction in the cooling capacity.

Therefore, according to a second exemplary embodiment of the invention, the cooling air ducts of the cooling air duct arrangement in the cylinder head are designed with a substantially constant cross section. As a result, flow losses, in particular due to cross-sectional changes, are reduced.

According to a third exemplary embodiment of the invention, the cooling air ducts of the cooling air duct arrangement in the cylinder head are designed with a continuously increasing (kontinuierlich vergroesserndem) cross section. As a result, flow losses that occur during sudden cross-sectional changes are avoided. At the same time, this advantageously results in a nozzle effect which again increases the cooling effect.

The first embodiment of the invention can advantageously be combined with the second or third embodiment for combining the advantages mentioned above.

Via the cooling air ducts of the cooling air duct arrangement, cooling gas, in particular cooling air, can flow into the exhaust duct (where it acts on the end of the exhaust valve facing away from the combustion chamber). In this case, the cooling of the exhaust valve, and in particular the cooling of the valve cone subjected to high thermal loads, takes place directly at the surface of the valve and thus takes place at a very favorable point in particular with regard to thermal corrosion. .

Charge air (Ladeluft) is preferably used as cooling medium. The cooling medium is generally referred to as air in the context of the present invention. However, other gases or gas mixtures can likewise be used to achieve the effect according to the invention.

Cooling air and/or cooling gas can be brought into the cylinder head from the outside via a supply system that is preferably connected directly to the charge air channel of the turbocharger of the internal combustion engine and/or by cooling The air channel assembly is connected to the intake channel (Einlasskanal) for inflow. In this configuration, the air is preferably guided from the intake duct to the exhaust valve without further pressurization.

The cooling air duct assembly according to the invention comprises at least one, preferably a plurality of cooling air ducts, which are advantageously designed and arranged in such a way that the cooling air flow flowing through them depends on the geometry of the exhaust duct (Geometrie ) and load the exhaust valve depending on the cooling requirement of the exhaust valve.

Exhaust valves usually have zones of different thermal loads. The valve foot guided in the cylinder head and controlled by the valve drive extends from the region on the valve drive with low thermal loads to the valve cone in which the valve is exposed to high thermal loads. Exit (Ventilkegelauslauf). In the case of two-part or multi-part valves which are joined between the valve foot and the valve cone, it is important to avoid too high a thermal load at the joint. The valve cone has a relatively high mass, which leads to a strong heat accumulation in this region. Due to the smaller surface of the valve cone, a reduced heat release occurs. Very high temperatures exist in the seat region of the valve, especially during the discharge of combustion gases. In the closed state, the seat region conducts this high temperature into the cylinder head via the valve seat, which is mostly cooled.

The cooling air channel arrangement is preferably adapted to the design of the cylinder head. Possible criteria for this adaptation are in particular the cooling jacket geometry or the required valve cooling. It is therefore advantageous if the cooling gas flowing out of a correspondingly configured and arranged cooling air duct has a high thermal load and/or a high dimensional accuracy (eg for sealing purposes) and Areas exposed to smaller temperature fluctuations should therefore be loaded. As mentioned above, these regions can include, in particular, the valve seat, the valve cone and/or the joints in the valve.

The cooling air ducts can be formed, for example, by means of a machining process such as drilling, or they can be additionally cast, for example, during the molding of the cylinder head.

In the region of the cooling air outlet from the cooling air duct to the exhaust duct, the cross section of the duct is preferably continuously increased in order to influence the cooling air flow. The resulting diffuser leads to an enlargement in the cross-section of the outgoing cooling air flow. A uniform cooling of a larger surface can be achieved, for example, by such a design.

In a refinement of the invention it is provided that the cooling air ducts of the cooling air duct arrangement conduct different cooling air volume flows into the exhaust ducts. In this way, for example, the velocity at which the cooling air flow impinges on the outlet valve and thus the cooling capacity can be influenced. Furthermore, the reachable range of this flow can be varied by means of an adapted volume flow.

Furthermore, due to the arrangement of the cooling air duct outlet openings with respect to their geometrical position in the exhaust duct relative to the exhaust valve, a significant influence on the achievable cooling effect results. Preferably, the cooling air ducts of the cooling air assembly are arranged at different heights in the axial direction of the outlet valve in order to obtain as uniform a cooling effect as possible over the circumference of the outlet valve. The arrangement of the cooling air channels is preferably also guided by the required cooling capacity at the valve cone or at the valve foot. Preferably, a plurality of cooling air channels are distributed radially relative to the axis of the outlet valve and/or have different inflow angles in order to achieve the desired cooling capacity.

The above features can be advantageously combined with one another. The cooling air ducts of the cooling air assembly can then be arranged at different heights in the axial direction of the exhaust valve in order thereby to increase the degree of freedom of creativity in the design of the cylinder head or to facilitate manufacturing. In order to achieve uniform cooling nonetheless, the cooling air channels which are further from the region of the valve to be cooled can conduct a larger cooling gas volume flow, in particular with a higher flow velocity.

Due to the high thermal load at the valve seat between the cylinder head and the seat area of the exhaust valve, separate high-strength elements such as seat rings or inserts are often arranged in the exhaust channel, which partially delimit the exhaust valve. gas channel. Preferably, no cooling air ducts run through such inserts, since the cooling air would be strongly heated when flowing through these regions subjected to very high thermal loads and the cooling effect would thus be impaired. Instead, in the cylinder head according to the invention in which such an insert is arranged, the cooling air channels are preferably formed in the actual cylinder head itself, in particular in the cylinder head housing. This also simplifies production.

Preferably, the cooling air duct of the cooling air duct arrangement is connected to the charge air duct of a turbocharger of the internal combustion engine. Furthermore, cooling air is preferably supplied continuously to the cooling air channel arrangement in order to cool the exhaust valves without interruption, independent of the working cycle in the combustion chamber.

The cooling air duct arrangement in the cylinder head according to the invention represents a structurally and technologically simple solution. Due to the thus improved cooling of the exhaust valves, it is possible to increase the operating temperature of the internal combustion engine, whereby a higher engine performance associated with improved combustion can be achieved. Furthermore, the service life of the valve cone can also be extended in the case of a cylinder head embodied according to the invention, since the risk of thermal corrosion is reduced due to the lower surface temperature at the rear of the exhaust valve.

Description of drawings

Further advantages, features and application possibilities of the invention are given by the following description in conjunction with the drawings. Here, the only

FIG. 1 shows a cross-sectional view of an exhaust channel with an exhaust valve of an embodiment of a cylinder head according to the invention.

List of reference numerals

10 cylinder heads

12 Exhaust channels

13 cooling jacket

14 seat ring

30 exhaust valve

31 seat area

32 valve cone

33 valve foot

41, 42 Cooling air channels

51, 52 Air flow

Detailed ways

FIG. 1 shows an exemplary embodiment of a cylinder head 10 according to the invention, which is shown in section in the region of an exhaust gas channel 12 . In the position shown, the exhaust valve 30 is seated in its seat region 31 . The exhaust channel is thus closed. In addition to the seat region 31 , the valve also includes a valve cone 32 and a valve foot 33 , which are mounted in the cylinder head outside the exhaust gas channel.

The cylinder head 10 itself is cooled by cooling water which circulates in a cooling jacket 13 which is only partially shown. The valve seat is formed by a separate valve seat ring 14 arranged in the cylinder head 10 , which is likewise water-cooled.

In the exemplary embodiment shown, the cooling air arrangement comprises two cooling air channels 41 and 42 which are introduced into the cylinder head 10 itself by means of bores in such a way that they run linearly through the cylinder head 10 . Cooling air ducts 41 and 42 act on valve 33 with cool air.

In this case, the two cooling air ducts are arranged in such a way that the exiting cooling air jet impinges directly on the valve cone 32 which is subjected to a high thermal load. The course of the air flow is indicated by arrows 51 and/or 52 in FIG. 1 .

For inventive reasons, in particular for an optimal arrangement and configuration of the cooling jacket 13 , and to simplify production, the two cooling air channels 41 , 42 of the cooling air channel assembly are arranged in the travel direction of the exhaust valve 30 (Hubrichtung) placed in different locations. In this case, in order to achieve a uniform loading of the valve cone, the cooling air channel 41 further away from the valve cone forms a sharper angle with the direction of travel of the exhaust valve, so that the cooling air flows at a higher normal direction (in Normalrichtung) Impulse (Impuls) and hit the valve cone. In a development not shown, the cooling air channel 41 opens slightly conically in the direction of the outlet valve 31 . The resulting nozzle effect likewise leads to an advantageous loading with cooling air which passes through the outlets of the cooling air channels arranged in different positions in the direction of travel.

The air turbulence induced by the incoming coolant flow in the exhaust channel 12 advantageously also increases the heat transfer from the valve cone to the cooling air leaving the cylinder head through the exhaust channel.

Claims (8)

1. A cylinder head (10), especially for a self-igniting internal combustion engine, has at least one exhaust passage (12), which can be closed by an exhaust valve (30); and has a cooling air passage assembly, which has At least one cooling air channel (41, 42) for impinging the exhaust valve (30) with cooling gas, in particular cold air, characterized in that the cooling air channel in the cylinder head (10) The cooling air ducts ( 41 , 42 ) of the component are designed approximately linearly and/or have an approximately constant or continuously increasing cross section. 2 . The cylinder head according to claim 1 , characterized in that the cooling air channel ( 41 , 42 ) widens in the region of the outflow to the exhaust gas channel ( 12 ). 3. The cylinder head according to any one of the preceding claims, characterized in that the cooling air channels (41, 42) of the cooling air channel assembly are connected to the charge air channels of the turbocharger or the intake air of the internal combustion engine The channels are connected. 4. The cylinder head according to any one of the preceding claims, characterized in that an insert (14) is arranged in the cylinder head (30) which partially delimits the exhaust gas channel (12) , and the cooling air passages (41, 42) of the cooling air passage assembly are constructed in the cylinder head (30) itself. 5. The cylinder head according to any one of the preceding claims, characterized in that at least two cooling air channels (41, 42) of the cooling air channel assembly are in the stroke direction of the exhaust valve (30) placed in different locations. 6. The cylinder head according to any one of the preceding claims, characterized in that at least two cooling air channels (41, 42) of the cooling air channel assembly are aligned with the stroke direction of the exhaust valve (13) form different angles. 7. The cylinder head according to any one of the preceding claims, characterized in that at least two cooling air channels (41, 42) of the cooling air channel arrangement guide different cooling air volume flows to the in the exhaust passage (13). 8. Cylinder head according to any one of the preceding claims, characterized in that the cooling gas acts on the exhaust valve (30) independently of the working cycle of the internal combustion engine.

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