Method of manufacturing a cylinder head of an internal combustion engine, cylinder head for an internal combustion engine, internal combustion engine and use thereof

Abstract

A cylinder head for an internal combustion engine. The cylinder head includes a cooling fluid cavity, the cooling fluid cavity being configured for enabling a flow of cooling fluid for cooling at least an exhaust valve portion of the cylinder head. The cooling fluid cavity includes at least one flow restrictor to restrict at least a first flow path of a plurality of flow paths of the cooling fluid within the cooling fluid cavity.

Description

[0001] TITLE OF INVENTION:

[0002] METHOD OF MANUFACTURING A CYLINDER HEAD OF AN INTERNAL COMBUSTION ENGINE, CYLINDER HEAD FORAN INTERNAL COMBUSTION ENGINE, INTERNAL COMBUSTION ENGINE AND USE THEREOF

[0003] Aspects of the invention relate to an improved cylinder head for an internal combustion engine, particularly a cylinder head having an improved cooling fluid cavity. The improved cylinder head may be particularly suitable for an engine utilizing an oil-based lubricant as the cooling fluid.

[0004] Technical background:

[0005] Straddled vehicles, such as motorcycles or other rideable vehicles, often include an internal combustion engine to propel the vehicle. In many cases, a lightweight and low-complexity internal combustion engine may be beneficial for the operator, e.g. due to low manufacturing, operating and maintenance costs, easy rideability, and low weight.

[0006] Modern internal combustion engines often are provided as single-cylinder, four-stroke petrol engines with a displacement of less than 400 cm2. Such engines may offer the above-stated advantages, while providing an adequate power output.

[0007] A cylinder head of an internal combustion engine generally includes valves, particularly intake- and exhaust valves, and optionally components associated with timing and operation of the valves. High temperatures may occur in the cylinder head particularly around the exhaust valve(s), in which hot exhaust gases are guided through the cylinder head into the exhaust system of the vehicle.

[0008] To prevent an overheating and / or damage of the cylinder head and / or the exhaust valves, the cylinder head may be cooled. Known cylinder heads include a cooling fluid cavity in which a cooing fluid, such as a water-based coolant, or an oil-based lubricant such as engine oil, are provided for cooling the area of the cylinder head around the exhaust valve(s).

[0009] A suboptimal flow path of the cooling fluid within the cooling fluid cavity may negatively impact the cooling efficiency. For example, an insufficient cooling fluid flow in a portion of the cooling fluid cavity may result in parts of the cylinder head overheating. Thus, there is a need for a cylinder head with an improved coolant flow, which maintains the above-stated benefits such as ease of manufacturing and low complexity.

[0010] The present invention solves the above-stated problem at least in part. Summary of the invention

[0011] In view of the above, a method of manufacturing a cylinder head of an internal combustion engine according to claim 1 , a cylinder head for an internal combustion engine according to claim 6, an internal combustion engine according to claims 10 or 11 , and the use of a cylinder head or an internal combustion engine according to claim 15 is described.

[0012] According to an aspect, a method of manufacturing a cylinder head of an internal combustion engine is described. The method includes providing a mold for casting, the mold defining outer surfaces of the cylinder head, placing a core in the mold to obtain a core-mold assembly, the core defining a cooling fluid cavity of the cylinder head, pouring a metal into the core-mold assembly to obtain a casting, separating the core-mold assembly from the casting, and inserting at least one flow restrictor into the casting. The flow restrictor is at least partially provided within the cooling fluid cavity to restrict at least a first flow path of a plurality of flow paths of the cooling fluid within the cooling fluid cavity. The method may in particular be carried out for manufacturing the cylinder head as described herein below.

[0013] According to an aspect, a cylinder head for an internal combustion engine is described. The cylinder head includes a cooling fluid cavity, the cooling fluid cavity being configured for enabling a flow of cooling fluid for cooling at least an exhaust valve portion of the cylinder head. The cooling fluid cavity includes at least one flow restrictor to restrict at least a first flow path of a plurality of flow paths of the cooling fluid within the cooling fluid cavity.

[0014] According to an aspect, a straddled vehicle is described. The straddled vehicle includes the internal combustion engine and / or the cylinder head according to aspects and / or embodiments described herein. The straddled vehicle may be a rideable vehicle. The straddled vehicle may be a light vehicle. Examples for straddled vehicles include, but are not limited to, motorcycles, motor scooters, motor rickshaws, other known examples of two- or three-wheeled vehicles, or snow mobiles.

[0015] According to an aspect, an internal combustion engine is described. The internal combustion engine may be a petrol-powered engine, such as an Otto engine. The internal combustion engine may be a single cylinder engine. The internal combustion engine may include more than one exhaust valve, such as two exhaust valves. In particular, the internal combustion engine may be a four-valve engine, such as an engine having two intake and two exhaust valves. According to an aspect, the internal combustion engine may have a capacity and / or displacement of 400 cm3or less, particularly 300 cm3or less, particularly 200 cm3, or even 165 cm3or less, such as about 160 cm3.

[0016] According to an aspect, the internal combustion engine may be at least partially air-cooled. In particular, a portion of the engine, such as cylinder walls of the engine, may be air-cooled. The engine being at least partially air-cooled does not exclude other portions of the engine from being cooled by other means than air.

[0017] Beneficially, the engine described herein may be lighter and / or have a lower parts count, e.g. compared to an engine having a capacity of more than 400 cm3, an engine having no aircooled portion, and / or a multi-cylinder engine. Beneficially, the engine described herein may be comparatively cost-efficient to manufacture and operate.

[0018] According to an aspect, a cylinder head is described. The cylinder head includes a cooling fluid cavity. During manufacturing, the cooling fluid cavity is typically defined by a core, such as a sand core, that is inserted into a mold before casting. It was observed that, particularly for smaller engines, such as the internal combustion described herein, the core may not have the required structural stability during casting when the core is shaped to define a cooling fluid cavity with complex structures. For example, a core defining a complicated, e.g. serpentinelike, flow path of a cooling fluid within the cooling fluid cavity would often break during casting.

[0019] Beneficially, the present disclosure allows the use of a stable core shape, while providing the desired shape of the cooling fluid cavity to define the intended flow path of the cooling fluid. Beneficially, the cylinder head described herein may offer improved cooling, and even improved lubrication, while manufacturing complexity remains low. Beneficially, the cylinder head described herein may be manufactured in an established manufacturing process, and / or require no or minimal re-tooling.

[0020] Further advantages, features, aspects and details that can be combined with embodiments described herein are evident from the dependent claims, the description and the drawings.

[0021] Brief description of the Figures:

[0022] The details will be described in the following with reference to the figures, wherein

[0023] Fig. 1 is schematic sectional plan view of a cylinder head according to embodiments;

[0024] Fig. 2 is a perspective view of a cylinder head interior during manufacture; Fig. 3a is a perspective view of a cylinder head interior according to embodiments;

[0025] Fig. 3b is a plan view of a cylinder head interior according to embodiments;

[0026] Fig. 3c is a sectional side view of a cylinder head interior according to embodiments; and

[0027] Fig. 4 is a method of manufacturing a cylinder head according to embodiments.

[0028] Detailed description of the Figures and of embodiments:

[0029] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations.

[0030] Within the following description of the drawings, the same reference numbers refer to the same or to similar components. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment applies to a corresponding part or aspect in another embodiment as well.

[0031] Methods according to embodiments described herein may be suitable for manufacturing a cylinder head according to embodiments. Features described with reference to a method of manufacturing a product may be applicable to products described herein, and features described with reference to a product may be applicable to the method of manufacturing the product.

[0032] Referring now to Fig. 1 , a cylinder head 100 according to embodiments is shown. Fig. 1 shows a sectional drawing of a cylinder head, i.e. shows an interior portion of the cylinder head 100. The cylinder head may be configured to be attached to a cylinder of an internal combustion engine. A sealing surface (not shown) may essentially be parallel to the drawing plane of Fig. 1.

[0033] The cylinder head includes a cylinder head body 104. The cylinder head body may be made of a metal, particularly a cast metal, such as aluminum, an aluminum alloy, steel, or a steel alloy.

[0034] As shown in Fig. 1 , the cylinder head includes valve insertion holes, particularly intake valve insertion holes 110 and exhaust valve insertion holes 112. Components of the valves, such as the valve stems, may extend through the valve insertion holes. Intake air and / or an intake air / fuel mixture may pass through the intake valve insertion holes 110, and exhaust gas may pass through the exhaust valve insertion holes 112. In the present example, the cylinder head 100 is a four-valve cylinder head, however, in some configurations, the cylinder head may have one to three intake valve insertion holes 110 and / or one to three exhaust valve insertion holes 112.

[0035] The cylinder head 100 includes a cooling fluid cavity 102. The cooling fluid cavity 102 is shown schematically in Fig. 1 and is embedded within the cylinder head body 104. The cooling fluid cavity 102 enables a cooling fluid to flow within and / or through the cooling fluid cavity 102. A cooling fluid may enter through the inlet 120, and flow through the cooling fluid cavity towards the outlet 122.

[0036] In the example shown in Fig. 1 , the cooling fluid cavity 102 encompasses the at least two exhaust valve insertion holes 112. The cooling fluid cavity 102 may essentially surround the at least two exhaust valve insertion holes, e.g. form a closed loop around the exhaust valve insertion holes 112. The closed loop may be interrupted, fully, or in part, by a flow restrictor, such as the flow restrictors 130, 132.

[0037] In the example shown in Fig. 1 , the cooling fluid cavity 102 does not fully encompass the intake valve insertion holes 110. In some embodiments, the cooling fluid cavity 102 may extend fully, or in part, into portion 106 of the cylinder head body 104. For example, the cooling fluid cavity 102 may further encompass one or more, or even all, of the intake valve insertion holes 110.

[0038] In the embodiment shown in Fig. 1 , the cylinder head 100, particularly the cooling fluid cavity 102, includes two flow restrictors 130, 132. The flow restrictors restrict a flow path of the cooling fluid within the cooling fluid body. As shown in Fig. 1 , the flow restrictor 130 restricts a flow of the cooling fluid along the flow path 142 as indicated by the arrow, and the flow restrictor 132 restricts a flow of the cooling fluid along the flow path 144 as indicated by the arrow. As shown in Fig. 1 , the flow restrictors 130, 132 are each provided at a position adjacent the exhaust valve insertion holes to restrict bifurcations of the flow of the cooling fluid around the exhaust valve insertion holes, such as a bifurcation splitting the fluid flow into the two flow paths 140 and 142, or splitting the fluid flow into the flow paths 140 and 144.

[0039] According to embodiments, restricting the flow by a flow restrictor may be understood as limiting the flow along the restricted flow path to less than 20 %, less than 10 %, less than 5 %, or even less than 2 %, such as 0-2 % compared to the volume flow of the unrestricted flow path. As a result of the flow restrictors 130, 132 being provided within the cooling fluid cavity 102, the cooling fluid flows unrestricted along the flow path 140 as indicated by the arrow, while the fluid flow along the flow paths 142 and 144 is restricted, or even fully limited and / or stopped. As shown in Fig. 1 , the unrestricted flow path 140 may be shaped and / or defined by the flow restrictors 130, 132. In particular, a cooling fluid flow at a desired location within the cooling fluid cavity 102 may be promoted by the flow restrictors 130, 132, and / or a cooling fluid flow at an undesired location may be restricted. According to embodiments, as shown in Fig. 1 , the unrestricted flow path 140 may be an essentially serpentine flow path, e.g. a flow path winding around the exhaust valve insertion holes 112. As shown in Fig. 1 , a portion of the serpentine flow path extends between the exhaust valve insertion holes 112. Beneficially, due to the presence of the flow restrictors 130, 132, only a limited amount, or even none of the cooling fluid bypasses the area of the cooling fluid cavity 102 in between the exhaust valve insertion holes 112, and cooling of the area in between the exhaust valve insertion holes may be improved.

[0040] According to embodiments, the flow restrictors 130, 132 may be structural elements which are separate from the cylinder head body 104. In particular, the flow restrictors 130, 132 may be formed in a process different than the casting of the cylinder head body. The flow restrictors 130, 132 may be inserts, pins, bolts, plates, sheets, welds, or any other type of known structure. In particular, the flow restrictors may be inserted into the cylinder head 100 after casting.

[0041] While in the example shown in Fig. 1 , a serpentine unrestricted flow path 140 was described as particularly beneficial, the invention is not limited to the embodiment shown in Fig. 1. In particular, only one, or more than two flow restrictors such as the flow restrictors 130, 132 may be provided. For example, one or more flow restrictors may be provided to alter the flow in the cooling fluid cavity 102 such that a flow of cooling fluid is locally improved, e.g. to avoid hot spots, which may be present at different locations in different cylinder head designs. In particular, the flow restrictors 130, 132 are arranged such that they force the cooling fluid to flow in the space between the pair of exhaust valve insertion holes 112, thereby allowing for a particularly effective cooling.

[0042] Referring now to Fig. 2, a perspective view of a cylinder head interior of a cylinder head 100 during manufacture is shown. In Fig. 2, the cylinder head body (ref. 104 in Fig. 1) is omitted for clarity. The cooling fluid cavity 102 is depicted as a solid body, e.g. as would be present in the form of a core in a core-mold assembly, however, it should be understood that the cooling fluid cavity 102 is an essentially empty (or e.g. water or oil-filled) volume in the cylinder head 100. More specifically, the cylinder head body extends around the cooling fluid cavity 102 so that the cooling fluid cavity 102 is embedded, as an open volume, within the cylinder head body.

[0043] As shown in Fig. 2, the cooling fluid cavity 102 may include a plurality of fin-like structures to improve heat transfer from the cylinder head body 104 to the cooling fluid, e.g. by increasing the surface area of the cooling fluid cavity 102 and / or by promoting a turbulent flow of a cooling fluid within the cooling fluid cavity 103.

[0044] Fig. 2 shows intake valves 210 and exhaust valves 220, as they would be present in an assembled cylinder head 100, for clarity. It should be noted that the valves do not form part of the cylinder head body, and may be provided during various stages of the cylinder head assembly. Likewise, the cylinder head 100 shows fluid channels connected to the inlet 120 and the outlet 122, which may be provided as channels within the cylinder head body 104 and / or at least in part, by components, such as conduits, not formed within the cylinder head body 104.

[0045] As shown in Fig. 2, no flow restrictors are present in the intermediate product. The cylinder head 100 shown in Fig. 2 may be configured for receiving flow restrictors, such as the flow restrictors 130, 132 shown in Fig. 1. For example, portions of the cylinder head body may be prepared for having flow restrictors inserted at one or more predefined positions. For example, a wall thickness of the cylinder head body 104 at a position at which a flow restrictor is to be inserted may be thinner to simplify providing an opening by e.g. drilling or otherwise providing a bore, or even include an opening. Accordingly, a core may be shaped to define the predefined openings.

[0046] Referring now to Fig. 3a, 3b and 3c, a cylinder head interior of a cylinder head 100 according to embodiments is shown in different perspectives. Fig. 3a shows a perspective view. Fig. 3b shows a plan view comparable to the view shown in Fig. 1. Fig. 3c shows a cutaway side view along the line A-A shown in Fig. 2.

[0047] The cylinder head 100 may be the cylinder head 100 shown in Fig. 2 after insertion of the flow restrictors 330, 332. Only the differences to Fig. 2 will be described. Each flow restrictor 330, 332 is provided at a position adjacent the exhaust valve insertion holes to restrict a flow of the cooling fluid in the cooling fluid cavity 102. As can be seen in Fig. 3a and Fig. 3c, the flow restrictors 330, 332 fully close off a fluid flow in the cooling fluid cavity 102, and thus fully restrict a flow of the cooling fluid past the flow restrictors 330, 332. In the embodiment shown in Fig. 3, the flow restrictors 330, 332 are provided as pins having an essentially cylindrical portion. Likewise, the flow restrictors may have an essentially conical portion, or even a shape deviating from a pin-shape, such as an ovoid or rectangular crosssection. The pins may be formed of a material, such as a metal, which may be the same metal as the cylinder head body. The pins may be suitable for being pressed into an opening, such as the opening described with reference to Fig. 2, for having the flow restrictors 330, 332 inserted therein. A flow restrictor, particularly a pin, may be press-fit into the cylinder head body 104.

[0048] According to embodiments, as can be seen in Fig. 3a and Fig. 3c, the flow restrictors may be inserted from any suitable position within the cylinder head. For example, the flow restrictor 330 is inserted through an opening provided at the gasket-side of the cylinder head, and the flow restrictor 332 is provided from the head-side opposite the gasket side of the cylinder head.

[0049] Referring now to Fig. 4, a method 400 of manufacturing a cylinder head of an internal combustion engine is described. The cylinder head may be the cylinder head 100 described herein with reference to Fig. 1 to Fig. 3a,b,c. The method 400 may be and / or include a method of manufacturing a casting of a cylinder head.

[0050] The method 400 includes providing 410 a mold for casting. The mold defines the outer surfaces of the cylinder head. Outer surfaces are to be understood as surfaces that can be accessed from the outside of the cylinder head, and may also include surfaces that, in the assembled state of the cylinder head and / or an internal combustion engine including the cylinder head may be considered inner surfaces.

[0051] The method 400 includes placing 420 a core in the mold to obtain a core-mold assembly. The core defines a cooling fluid cavity of the cylinder head, such as the cooling fluid cavity 102. The cooling fluid cavity may be considered an inner surface of the cylinder head.

[0052] According to embodiments, the mold and / or the core may be formed of a casting sand commonly known in the art. Accordingly, the method 400 may include a sand casting process.

[0053] According to embodiments, the core may be shaped to be stable in a casting process. For example, the core may have a closed outer circumference, defining e.g. the circumference of the cooling fluid cavity 102 shown in Fig. 1 . The core may include one or more openings, such as the openings provided about the exhaust valve insertion holes 112 shown in Fig. 1 such that the core may define at least one loop of core material around the openings, and / or at least one torus being constructible from the core. The core may be devoid of serpentine sections defining a serpentine cooling fluid flow in the cooling fluid cavity.

[0054] The method 400 includes pouring 430 a metal into the core-mold assembly to obtain a casting. The metal may be a molten metal. The metal may be an aluminum alloy and / or a steel alloy. The casting may be a workpiece suitable for manufacturing the cylinder head therefrom. For example, the casting may be further processed to obtain the cylinder head. Further processing may include machining, assembly and / or providing peripheral components.

[0055] The method 400 includes separating 440 the core-mold assembly from the casting. Separating 440 may include removing the casting from the mold. Separating 440 may include removing the core from the casting, i.e. removing the core and / or the core material from the cooling fluid cavity. Accordingly, the core may be a sacrificial core.

[0056] The method 400 includes inserting 450 at least one flow restrictor into the casting. The flow restrictor is at least partially provided within the cooling fluid cavity. The flow restrictor restricts at least a first flow path of a plurality of flow paths of the cooling fluid within the cooling fluid cavity. In particular, the flow restrictor may restrict, or even fully prevent, a bifurcation of a flow of the cooling fluid. The flow restrictor may be provided adjacent an exhaust valve insertion hole.

[0057] Inserting 450 the at least one flow restrictor may include forming at least one bore in the casting. The bore extends from an outer surface of the casting into the cooling fluid cavity. Forming the bore may include drilling, boring, or any other type of machining. Forming the bore may be included in the further processing of the casting. The inserting 450 may include pressing in a flow restrictor workpiece into the bore. The flow restrictor workpiece may be the flow restrictor, or may be further processed to form the flow restrictor. For example, and not limited thereto, after inserting the flow restrictor workpiece, a portion of the flow restrictor workpiece, such as an outside portion, may be further machined to form the flow restrictor. For example, the flow restrictor workpiece may be a pin. The flow restrictor workpiece may be press-fit into the casting.

[0058] According to particularly beneficial embodiments, press-fitting the flow restrictor workpiece may be sufficient to securely insert and / or seal the flow restrictor workpiece in the casting and / or a cylinder head body. Beneficially, no further processing of the flow restrictor workpiece and / or the casting is required to secure the flow restrictor inside the cooling fluid cavity, which may simplify manufacturing of the cylinder head. It should be understood that the processing of the casting to obtain the cylinder head may be performed in a variety of sequences. Accordingly, the at least one flow restrictor may be inserted 450 into the casting at any point during the manufacture of the cylinder head, and inserting 450 the flow restrictor into the casting may be understood as inserting the flow restrictor into the cylinder head.

[0059] According to embodiments, an internal combustion engine is described. The internal combustion engine includes the cylinder head according to an embodiment described herein, and / or the cylinder head as obtained by a method described herein.

[0060] In a first embodiment, the cooling fluid of the internal combustion engine, i.e. the cooling fluid provided in the cooling fluid cavity 102 is a water-based coolant. Accordingly, the internal combustion engine may include a cooling circuit including a water pump, a radiator, and any other components know in the art. The cooling circuit may be connected to the inlet 120 and the outlet 122, e.g. in a closed loop.

[0061] In a second embodiment, the cooling fluid of the internal combustion engine, i.e. the cooling fluid provided in the cooling fluid cavity 102 is an oil-based lubricant (“oil”). In particular, the cooling fluid may be an engine oil being utilized both as a cooling fluid and a lubricant, e.g. for lubricating bearings or other moving parts of the internal combustion engine.

[0062] For example, the inlet 120 shown in Fig. 1-3c may be an inlet for receiving the oil, and the outlet 122 may be an outlet for letting out the oil after the oil has passed the cooling fluid cavity 102. The outlet 122 may be fluidly connected to a lubrication system. In particular, the lubrication system may be a lubrication system of the cylinder head, such as a lubrication system for lubricating valve timing components, such as a bearing, particularly a bearing of the cylinder head, such as a camshaft bearing. Thereby, the cylinder head provides an oil path for the oil according to which the oil is transported in series through the cooling fluid cavity 102 for cooling and thereafter to the lubrication system for lubricating. Compared to a parallel oil flow, this maximizes the amount of oil transported through the cooling fluid cavity 102 for cooling.

[0063] According to embodiments, the inlet 120 may be the only oil inlet of the lubrication system of the cylinder head of the internal combustion engine. In particular, all the oil utilized for lubricating the cylinder head may flow through the cooing fluid cavity, particularly without branching off separate oil channels for the lubrication system and the cooling system. This may beneficially allow a simple and efficient design of the cylinder head, such as the complexity of the oil gallery, e.g. by reducing the number of required oil channels. Beneficially, it has been observed that in an internal combustion engine according to embodiments, the oil is provided at adequate pressure, flowrate and temperature to the lubrication system of the cylinder head after having passed the cooling fluid cavity.

[0064] According to embodiments, the lubrication system of the internal combustion engine includes an oil pump, particularly a single oil pump. The inlet 120 may be connected to an outlet of the oil pump, and the outlet 122 may be connected to an inlet of the oil pump. In particular, the oil pump and the cooling fluid cavity may be connected serially and / or in a closed loop. The closed loop may further include the lubrication system of the cylinder head and an oil reservoir, such as an oil sump. It should be noted that other lubrication systems of the internal combustion engine, such as an engine block lubrication system, may be branched off in a separate loop, and are not considered as included in the closed loop.

[0065] According to embodiments, the use of a cylinder head and / or an internal combustion engine according to embodiments described herein in a vehicle is described. Beneficially, the cylinder head according to embodiments may be compatible with existing engine designs. Beneficially, the internal combustion engine may be compatible with existing straddled vehicles. Accordingly, the use may involve providing the improved cylinder head and / or the improved internal combustion engine in place of a known cylinder head and / or internal combustion engine.

[0066] While the disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention, and the invention is defined by the claims that follow.

Claims

\Ne Claim:

1. Method of manufacturing a cylinder head of an internal combustion engine, comprising: providing a mold for casting, the mold defining outer surfaces of the cylinder head; placing a core in the mold to obtain a core-mold assembly, the core defining a cooling fluid cavity of the cylinder head; pouring a metal into the core-mold assembly to obtain a casting; separating the core-mold assembly from the casting; inserting at least one flow restrictor into the casting, wherein the flow restrictor is at least partially provided within the cooling fluid cavity to restrict at least a first flow path of a plurality of flow paths of the cooling fluid within the cooling fluid cavity.

2. The method as claimed in claim 1, wherein the metal comprises an aluminum alloy, and wherein the flow restrictors comprise an aluminum alloy.

3. The method as claimed in claim 1 or 2, wherein inserting the at least one flow restrictor comprises: forming at least one bore in the casting, the bore extending from an outer surface of the casting into the cooling fluid cavity; and inserting the at least one flow restrictor comprises pressing in a flow restrictor workpiece into the bore.

4. The method as claimed in claim 3, wherein the flow restrictor workpiece comprises an essentially cylindrical or conical portion.

5. The method as claimed in any one of claims 1 to 4, further comprising: processing the casting to obtain the cylinder head.

6. Cylinder head for an internal combustion engine, comprising: a cooling fluid cavity, the cooling fluid cavity being configured for enabling a flow of cooling fluid for cooling at least an exhaust valve portion of the cylinder head, wherein the cooling fluid cavity includes at least one flow restrictor to restrict at least a first flow path of a plurality of flow paths of the cooling fluid within the cooling fluid cavity.

7. The cylinder head as claimed in claim 6, wherein the cylinder head comprises at least two exhaust valve insertion holes; and the cooling fluid cavity encompasses the at least two exhaust valve insertion holes.

8. The cylinder head as claimed in claim 7, wherein the at least one flow restrictor is provided at a position adjacent the exhaust valve insertion holes to restrict at least one of a bifurcation of a flow of the cooling fluid around the exhaust valve insertion holes.

9. The cylinder head as claimed in claim 7, wherein the at least one flow restrictor is provided at a position adjacent the exhaust valve insertion holes to direct a flow of the cooling fluid into a serpentine flow path around the exhaust valve insertion holes, a portion of the serpentine flow path extending between the exhaust valve insertion holes.

10. An internal combustion engine comprising the cylinder head as claimed in any one of claims 6 to 9, wherein the cooling fluid is a water-based coolant.

11. An internal combustion engine comprising the cylinder head as claimed in any one of claims 6 to 9, wherein the cooling fluid is an oil-based lubricant.

12. The internal combustion engine as claimed in claim 11, whereinthe cooling fluid cavity comprise an inlet for receiving the oil-based lubricant, and an outlet for the oil-based lubricant, and wherein the outlet of the oil-based lubricant is fluidly connected to a lubrication system, the lubrication system being configured for lubricating a bearing of the cylinder head.

13. The internal combustion engine as claimed in claim 12, wherein the lubrication system comprises an oil pump, the inlet of the cooling fluid cavity being connected to an outlet of the oil pump, and the outlet of the cooling fluid cavity being connected to an inlet of the oil pump in a closed loop.

14. The internal combustion engine as claimed in any one of claims 10 to 13, the internal combustion engine being at least one selected from the group consisting of: an Otto engine; a single cylinder engine; a four-valve engine; an engine having a displacement of 400 cm3or less; an at least partially air-cooled engine.

15. Use the cylinder head as claimed in any one of claims 6 to 9, or the internal combustion engine as claimed in any one of claims 10 to 14 in a vehicle, wherein the vehicle is a straddled vehicle.

Images