DE8521358U1 - Piston for a diesel internal combustion engine - Google Patents

Description

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Piston for a diesel engine

The invention relates to a piston for a diesel internal combustion engine with direct injection and a swirl-generating intake port, wherein a piston recess and valve pockets for intake and exhaust valves are provided in the piston crown.

It is known that in such diesel internal combustion engines with direct injection, the mixture formation in the cylinder can be significantly improved if the combustion air enters the cylinder with a swirl, so that an air vortex is generated around the cylinder's longitudinal axis. At the end of the compression stroke, a squish flow is also created that is directed radially towards the piston recess.

For satisfactory mixture formation, a stronger swirl is required at low speeds than at high speeds, and the intake port must be designed in such a way that the required strong swirl is generated at low speeds. Since the throttling effect of the intake port is greater the stronger the swirl, an intake port optimized for swirl at low speeds results in relatively large throttling losses at high speeds, which reduces the performance and efficiency of the internal combustion engine at high speeds. Measures are already known to change the swirl depending on the speed, so that the intake port is optimized for high speeds and the swirl for low speeds is increased by flaps or other means to the level required for mixture formation at these speeds. However, these measures are complex and have not been able to prevail in practice.

The invention is based on the object of creating a diesel internal combustion engine of the type mentioned at the beginning, in which a strong swirl is achieved at low speeds without flaps or other movable control elements, but the throttling effect of the swirl-generating inlet channel is considerably reduced at high speeds.

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This object is achieved according to the invention in that the edge of the valve pockets in the piston crown is rounded and/or bevelled.

Surprisingly, it has been found that the edge of the valve pockets, which has previously been sharp-edged, with the peripheral wall of the valve pockets at a right angle to the piston crown, greatly slows down the swirl of the incoming combustion air. Therefore, the intake port had to be designed in such a way that at low speeds a very strong swirl is created, which despite the mentioned

iö braking strongly enough to enable satisfactory mixture formation, but on the other hand led to considerable power losses at high speeds.

The proposal according to the invention slows down the swirl considerably less, so that the intake port can be designed to produce less swirl at low speeds, thereby reducing the throttling effect at high speeds and increasing the power and efficiency accordingly.

An embodiment of the invention is described below with reference to the drawings. It shows:

Fig. 1 a top view of the piston crown _y
Fig. 2 is a section along line 2 - 2 in Figure *\ _t and Fig. 3 is a section along line 3 - 3 in Fig. 1 on a larger scale.

The piston 1 shown in the drawings has in its piston crown 2 a piston recess 3 as well as valve pockets 4 and 5 into which the valve plates of the associated valves protrude in the top dead center position of the piston 1, as shown in dashed lines in Figure 3 for the inlet valve 6.

Previously, the edge of the valve pockets was designed with sharp edges, as indicated by the dashed line at 7 in Fig. 3. This slows down the air flow circulating in a swirl around the piston center axis, which is illustrated by the arrows 8 in Fig. 1, since this edge on the inlet side of the air flow into the valve pockets acts as a separation edge that creates vortices, and the edge on the outlet side acts as a stagnation surface.

In order to avoid or at least reduce this slowing down of the swirling movement of the air flow, the edge 9 of the valve pockets 4, 5 is bevelled according to the invention, as can be clearly seen in Fig. 2 and 3. This ensures that the air flow can flow through the valve pockets without significant obstruction, as is illustrated by the arrows 10 in Fig. 3. It has been shown that with this simple measure the mean pressure can be increased considerably at low speeds, so that a swirl channel with less swirl and correspondingly less throttling can be used at high speeds. The angle Gt between the bevelled peripheral wall 9 and the vertical should be at least 30°. The edge 9 does not have to be formed by a straight surface, but can also be rounded.

Claims (2)

&bull; ·»!··■ a &igr; * * it· ■ · ( · I ■■ ■ 303/85 AUDI AG, 8070 Ingolstadt Piston for a diesel internal combustion engine --ft-t Hnsprüche 1. Piston for a diesel internal combustion engine with direct injection and a swirl-generating intake channel, wherein a piston recess and valve pockets for intake and exhaust valves are provided in the piston crown, characterized in that the edge (9) of the valve pockets (4, 5) in the piston crown (2) is bevelled and/or rounded. 2. Piston according to claim 1, characterized in that the bevel of the edge (9) of the valve pockets (4,5) is at least 30°. ti it*