DE448268C - Pistons for heat engines - Google Patents

Description

GERMAN EMPIRE

ISSUED ON AUGUST 15, 1927

REICH PATENT OFFICE

PATENT LETTERING

CLASS 47 f GROUP

Raymond de Fleury in Paris and Jacques Floquet in Levallois-Perret, Seine, France.

Pistons for heat engines. Patented in the German Empire on June 13, 1925.

The invention relates to an engine piston for heat engines. The invention consists in that the forming the inner bottom of the piston, in a manner known per se butting cones have such an obtuse apex angle that a more uniform The heat is drained after the cylinder wall.

The piston crown thickness is necessary for the purpose of a uniform temperature of the piston surface in the center of the bulb enlarged according to the radiation at the individual points and reduced at the edge of the piston. Fig. Ι shows the geometric development for the profile of the piston crown.

Fig. 2 combines two structural embodiments developed from Fig. 1, which are separated from each other by a common center line.

Fig. 3 to 6 show further embodiments.

The most important characteristic of the piston is that it has particularly large cross-sections, which allow good dissipation of the heat absorbed by the piston crown. The cross-sections change in

Function of the amount of heat absorbed, ie as a function of the surface of the piston crown. If you strike concentric circles with the radii p, r and R around the center ο (axis XY of the piston) of the piston crown, then represent the recorded in a time dt . Thermal elements are a function of the areas of the ring given by circles. Their relationship, expressed in an equation, is:

Sj

(R ^z -r ² \

= η - = m:

\ r ^z - ρ ² !

The mean piston crown thicknesses e ^x -e therefore also have a certain relationship among themselves. On the other hand, since in theoretical centers ο there is no question of absorption (theoretically this would mean a piston crown thickness equal to zero), the generating line O, N of the conical piston crown underside must be a straight line passing through point O. The calculation shows that there is good cooling as soon as the angle at the tip of this conical surface has the value 135 ⁰ . A decrease in its angle would mean an increase in cooling. The base of that cone depends on how the point α on the generating line O, N is determined. Point α should be at the same distance from the outer surface of the piston crown and from the piston side wall. Accordingly, its position is determined by the intersection of the straight lines O, η and the bisector of the right angle 0, x, n. With the determination of the position of the point α , the wall thickness e ^{3 is} determined at the same time.

The connection of that conical surface with the inner piston side wall is done by plotting a distance xm = xn on xo, starting from x, and drawing the straight line m α through the point m , which the inner piston wall of thickness e ² at one point b cuts. The straight line or generating line α b also creates a conical surface. The calculation of the angles reveals that the angle at the apex of this cone is 45 ° if the angle at the apex of the other cone 13S is ⁰ . The inner wall of the piston crown is thus delimited by two conical, intersecting or penetrating surfaces, with the tip of the cone lying exactly in the center of the outer wall of the piston crown. The point angles of both cones add up to i8o ° (135 ⁰ + 45 ° == i8o °). For an even more intensive cooling, the tip angle of 120 ° ⁰ and 6o are selected (120 ⁰ + 60 ° = i8o °). With these ratios, the greatest thermal conductivity is given with the greatest lightness. In practice and for reasons of strength, however, the piston cannot be built entirely according to the theoretically determined outlines. For example, the piston cannot be given a wall thickness equal to zero in the center of the piston crown, and so the design shown in the left half of Fig. 2 is the result. The dash-dotted lines indicate that the outer surface of the piston can also be raised in relation to the profile of the inside, the profile of the inside can remain the same if one wants to achieve greater wall thicknesses and consequently greater resistance or greater strength. A very similar profile can also be obtained by drawing the envelope curve to the straight lines or generators Oa - ab. Compare the right half of Fig. 2.

If the outside of the piston head is arched, the profile _{t of} the inside can finally be redesigned in such a way that the piston head thicknesses determined with the aid of the cones for flat piston heads are also maintained for the arched head.

According to the information given above, pistons are obtained which actually do not change their shape subject, although the material used for their production (light metal) is of high thermal conductivity, e.g. B. an aluminum alloy or an aluminum silicon or aluminum magnesium alloy. In addition to this high conductivity, the pistons have particularly large cross-sections own and that thereby the cooling mainly by conductivity, not but only and as it is with the light metal pistons in use now Case is caused by radiation or convection. So the new piston is a Diatermal light metal piston, but due to its large cross-sections in comparison is relatively heavy compared to the known aluminum pistons.

The designated cooling requires, for each concentric circle of the piston head, heat passage cross-sections which are the same as the absorption areas, ie the concentric circular areas in question. Such a condition "requires for each circle a piston crown thickness proportional to the radius of the circle in question, whereby it must be taken into account that the path traversed by the heat is much greater for pistons with a larger bore. It is therefore common, quite Provide a height h on the circumference of the piston crown for cooling equivalent to the cooling of smaller pistons. Of course, the height h for the first piston type is relatively greater than for the second type of piston. The height h also falls

Claims (2)

with the same effect and with the same piston size, it is much smaller if an even more conductive metal should be used to manufacture the piston instead of a less conductive material. It can be seen that the paths to be traversed by the heat, based on the cross-sectional unit in question for the absorbed heat, are, under such circumstances, much longer for the central parts of the piston crown than for the parts of the crown located on the circumference, and that from this a mean one Compensation temperature results, which is significantly higher in the center of the piston crown than on the circumference of the piston crown. Since during the operation of an engine the local temperature of a more heated point, especially with a larger piston, gives rise to malfunctions and the service life of the machine or piston is shortened, the invention aims to prevent this and increase operational reliability at the same time by attempting to lower the local temperature in the center of the piston crown and progressively with the imaginary concentric circles in that the absorbed heat, e.g. B. the absorbed heat for the concentric circle with the radius X, a passage cross section is made available which, based on the unit of heat absorption surfaces, in which. Dimensions become larger as the respective circle in question moves away from the surrounding area with the height α. The means by which this result can be achieved consist in the fact that the piston crown for a given height /; wall thicknesses are given for heat dissipation, the sizes of which can be determined for each point by the following equation (Fig. 5): Yn- IYn ^ Ä_ Xn- T-Xn "r 'This refers to the surface element of the conical or concave piston crown inner surface, especially for the In the event that the bottom has a completely flat surface on the outside. The advantage of such a profile is that the piston not only shows a lowest mean temperature, but also has the lowest local temperatures for a minimum of the material used. | In no way excludes the use of a conical surface with a convexly curved generatrix. With such conical surfaces, the point in the center of the piston head is appropriately blunted (Fig. 6). Not excluded are pistons with a uniform elevation, otherwise but has the same characteristics for the inside (dotted line in Fig. 6). It is also not excluded that the To connect the inner walls of the piston with the inner walls of the piston crown by free lines in such a way that simply rounded or truncated corners or hyperbolically curved, inward or outward corners are formed, through which at the same time certain cross-sections beyond the bottom for heat dissipation and more efficient distribution of heat to the side walls of the Pistons arise. In other words, a larger section of the piston running surface is used for intensive cooling. On the other hand, at least in the case that it is a piston with a flat bottom, the latter is characterized by the convex curvature of the surrounding surfaces, similar to a conical surface, as well as by the lines at the point where the two generators of the inside of the piston crown touch each other . The same law of change in the wall thickness of the piston crown applies to pistons with a domed crown. Of course, the enlargement of the wall thickness caused by the arched bottom would have to be taken into account accordingly. The various embodiments specifically require the manufacture of light metal, which at least allows large heat-conducting cross-sections to be constructed with a lower weight. PaTKnt claims: 1. Pistons for heat engines, characterized in that the Inner bottom of the piston forming, in an icn As is known, butting cones have such an obtuse apex angle that a uniform discharge the heat after the Zyjinderwandung takes place. 2. Arrangement according to claim 1, characterized in that for the purpose of more uniform The temperature of the piston surface, the thickness of the piston crown in the center of the piston is proportional to the radiation is increased in every point and decreased at the edge of the piston. 1 sheet of drawings.