The invention relates to a poppet valve, in particular a hollow poppet valve. Poppet valves are for example used in combustion engines to open and close the inlet and outlet ports to the cylinders. As the power of combustion engines increases, the heat production also increases. To this end it is known to provide hollow poppet valves, which are filled with for example sodium for better heat exchange.

In order to maximize the heat exchange of hollow poppet valves and with the aim of reducing knocking tendency of gasoline engines, the cavity in the valve head should be as large as possible. A number of manufacturing methods are known to produce such poppet valves.

For example US 2016356186 proposes a valve, in which a valve body is provided with a cavity opening at an axial end. This cavity is closed by a valve cap, which is welded to the valve body. The weld is arranged in the axial end surface of the valve, such that the weld is directly subjected to the heat of the combustion process. This could result in fatigue of the weld and as a result leakage of the sodium in the hollow poppet valve into the cylinders of the combustion engine .

Other manufacturing methods are known, in which the valve head is formed as one piece. For example JP 1995208127 disclosed a method in which a hollow valve head is shaped out of a solid material. The resulting cavity, especially in the head itself, is very limited.

Also US 20120255175 discloses a method in which a rod with a blind hole is shaped into a poppet valve. Also with this method, the size of the cavity of the valve head is limited .

Accordingly, it is an object of the invention to reduce the above mentioned disadvantages.

This object is achieved with a poppet valve according to the invention, which poppet valve comprising:

- a valve stem;

- a valve body having along a longitudinal axis a first end with a neck portion to which the valve stem is coaxially arranged and having along a longitudinal axis a second end with a first conical contact face portion, wherein the valve body comprises a cavity with a first opening towards the first end and a second opening towards the second end;

- a valve cap coaxially arranged to the valve body on the second end for closing the second opening, wherein the valve cap has a second conical contact face portion to form together with the first conical contact face portion a valve head contact face.

With the poppet valve according to the invention, the valve body is manufactured with a cavity having a second opening towards the second end. This second opening is closed by the valve cap. Because the valve cap provides for a second conical contact face portion, which forms together with the first conical contact face portion a valve head contact face, the partition surface between the valve body and the valve cap is no longer positioned in direct contact with the combustion process in the cylinder. This ensures that the impact of the combustion process onto the attachment between the valve body and the valve cap is lower, such that the chance on leakage of sodium or the like from the cavity is reduced.

In a preferred embodiment of the invention according to the invention both the first and second conical contact face portions comprise a circumferential groove portion to form together a circumferential face groove and wherein a layer of seat facing material, for example cobalt based or iron based, is arranged in the circumferential face groove.

The circumferential groove provides for a space to arrange a seat facing material and covering the partition surface, such that the partition surface between the valve body and the valve cap is shielded from any contact with the combustion process in the cylinder.

In a further preferred embodiment of the poppet valve according to the invention the valve cap is welded to the valve body, which weld is arranged between the first and second conical contact face portions.

In yet another embodiment of the poppet valve according to the invention the valve cap comprises a

cylindrical upright wall, which extends into the second opening of the cavity and centers the valve cap relative to the valve body.

The upright wall allows for an easy positioning of the valve cap into the cavity of the valve body, but also provides for absorption of forces between the valve cap and the valve body, such that the weld between the valve body and valve cap is at least partially relieved from stresses between the valve body and the valve cap.

In still another embodiment of the poppet valve according to the invention the valve stem comprises a stem cavity with an opening connecting to the first opening of the cavity of the valve body.

With the stem cavity connected to the cavity of the valve body, the poppet valve is provided with a cavity

extending through the whole poppet valve. This cavity can be filled with sodium or the like to enhance the heat transfer of the valve, with a reduction of the chance on leakage compared to prior art poppet valves.

In yet a further preferred embodiment of the poppet valve according to the invention the valve body further comprises a first annular contact face portion arranged coaxial with the longitudinal axis of the valve body and a first conical weld surface extending under an angle from the first conical contact face portion, wherein the first annular contact face portion transitions in radial outward direction into the first conical weld surface; and

wherein the valve cap further comprises a second annular contact face portion arranged coaxial with the

longitudinal axis of the valve cap and a second conical weld surface extending under an angle from the second conical contact face portion, wherein the second annular contact face portion abuts the first annular contact face portion and the first and second weld surfaces face each other.

The contact between both annular contact face portions ensure that any stresses between the conical weld surfaces and especially in the weld are reduced or even prevented .

Preferably, the radius of the outer edge of the first annular contact face portion is smaller than the radius of the outer edge of the second annular contact face portion, such that a space is formed between the first conical contact weld surface and the second annular contact face portion.

By providing a space between the first conical weld surface and the second annular face portion a space for any welding residual is provided, which avoids the the starting of cracks in the weld.

The invention also relates to a method for manufacturing a poppet valve according to the invention, which method comprises the steps of:

- providing a poppet valve according to any of the preceding claims, wherein the valve body is provided by machining and / or welding and / or forming; - welding the valve cap and valve body together by arranging a weld between the first and second conical contact face portions; and

- covering the weld by a layer of seat facing material.

In a preferred embodiment of the method according to the invention the weld is covered by a layer of seat facing material using plasma transferred arc welding. Plasma

transferred arc welding allows for a variety of materials to be arranged in the circumferential face groove, especially for relative hard materials, which are very suited for a valve seat surface. Other options to arranged the layer of seat facing material are by laser welding and projection welding.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

The figure 1 shows a cross sectional view of an embodiment of a poppet valve according to the invention with an enlarged part of the valve head.

Figure 2 shows a cross sectional view of a second embodiment of a poppet valve according to the invention.

The figure 1 shows a poppet valve 1 with a valve stem 2, a valve body 3 and a valve cap 4.

The valve stem 2 has a cavity 5, which connects to a cavity 6 of the valve body 3 via a first opening at the first end 7 of the valve body 3. The second opening of the valve body 3 is closed by the valve cap 4.

The valve body 3 is provided along a longitudinal axis at a second end with a first conical contact face portion 8. The valve cap 4 is provided with a second conical contact face portion 9, with forms together with the first conical contact face portion 8 a valve head contact face.

Each conical contact face portion 8, 9 is provided with a groove portion, which accommodates a layer of seat facing material 10, which covers the weld 11 between the valve body 3 and the valve cap 4.

The valve cap 4 is provided with a cylindrical upright wall 12, which mates with a circumferential wall 13 of the cavity 6 and ensures that the valve cap 4 is centered relative to the valve body 3.

Figure 2 shows a poppet valve 20 with a valve body 21 and a valve cap 22. The valve body 21 has a first conical weld surface 23, which transitions into a first annular contact face portion 24. The valve cap 22 has a second conical weld surface 25 and a second annular contact face portion 26.

The outer radius ri of the first annular contact face portion 24 is smaller than the outer radius r ₂ of the second contact face portion 26, such that a space 27 is provided between the first conical weld surface 23 and the second annular contact face portion 26.

The weld to attach the valve body 21 to the valve cap 22 is arranged between the first conical weld surface 23 and the second conical weld surface 25. Any residuals of the weld can flow into the space 27, preventing any cracks

occurring the in the weld.

The first and second annular contact face portions 24, 26 furthermore reduce any stresses in the welding area.