GB1603534A

GB1603534A - Piston for reciprocating internal combustion engines typically diesel engines

Info

Publication number: GB1603534A
Application number: GB14645/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-04-18
Filing date: 1978-04-13
Publication date: 1981-11-25
Also published as: FR2388140A1; JPS6131293B2; IT7805176A0; NL184535B; IT1102201B; JPS549312A; DE2717028A1; DD136411A1; NL7804113A; IN150508B; DE2717028C2; ZA782176B; JPH01179153U; HU177087B; SE7804342L; YU90278A; BR7802414A; NL184535C

Description

(54) PISTON FOR RECIPROCATING INTERNAL COMBUSTION ENGINES, TYPICALLY DIESEL ENGINES (71) We, LUDWIG ELSBETT and GÜN- TER ELSBETT, both German citizens and both of D-8543 Hilpoltstein, Industriestrasse 14, Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement::- The invention relates to a piston for reciprocating internal combustion engines, typically Diesel engines, having a crown exposed to the heat of the combustion gases and a shell connecting said crown with a guide member which only transmits normal forces as well as a ring carrier connected to the crown of the piston and provided with sealing and oil control rings which ring carrier is connected via a construction situated in the region of a plane containing the crown of the piston and in which piston the shell connecting the crown with the guide member has a base formed by two forkshaped legs at its end opposite to the crown with said legs being arranged symmetrically to a plane extending through the centre of the piston and provided with eyes for a wrist pin connecting the base with the guide member.

There is a marked trend in modern design practice for reciprocating internal combustion engines, e.g. Diesel and Otto cycle engines, towards attaching increasing importance to the component "piston". If, for instance, it was formerly usual practice to adopt a heavy and complex piston, the tendency today is more and more towards the lighter weight piston, one reason being in the ever higher speeds of the engines, without, however, sacrificing the life expectancy of such pistons.

A known piston for such high-speed reciprocating internal combustion engines, typically for Diesel engines, is essentially formed by a ring carrier connected to the crown of the piston and a shell connecting said crown with a base, the shell being in the shape of a hollow casing and enclosing a combustion chamber in the shape of a solid of revolution.

Also as a result of the type of combustion system used, the combustion chamber in this piston is subdivided in two sections, one of the sections which faces a combustion chamber opening in the crown of the piston being constructed for heat insulation whereas the other section adjacent to the base of the piston is heat conducting. With a view to enhancing the desired heat insulation, the heat insulating section of the piston is provided with a heat insulating insert and the shell of the piston itself, especially in the region of the crown at the one end and in the region of the base of this piston at the other end is formed with reductions in area which act to throttle the heat flow.This type of piston permits very efficient temperature control of the combustion chamber according to a heat pattern matched to a preselected and specific combustion process so that, in addition to optimization of the combustion reactions between the fuel and the air for combustion on the one hand lower stress levels of the sealing and oil control rings on the ring girder on the other hand are achieved. Pistons of this type have given good results as far as their properties in respect of the combustion process and the stress levels of sealing and oil control rings are concerned, but it has appeared desirable in view of the increasing power rating of internal combustion engines to review their strength (see German Patent Application P 25 45 588.3-13).

Accordingly, it is desirable to improve specifically a piston of the aforementioned type to permit its strength to be determined in a straightforward manner for all piston diameters and also to make this adequately possible with the least possible cost of materials.

This problem is resolved according to the present invention in a piston of the type initially referred to in that the shell of the piston between the crown and the base thereof is designed as a cone in the shape of a body of revolution and that said shell with its supporting plane at the base of said cone is attached to the crown and with a further plane opposite to the latter is connected to the base of the piston and in that the diameter of the supporting plane at the crown relative to the diameter of the supporting frame at the base is in a ratio of substantially 2: 1.

These features provide a piston which not only advantageously fulfills the task underlying the invention but, in addition to that, on the strength of its shape being substantially that of a body of revolution, permits its individual sections to be very conveniently manufactured. The piston so formed can be designed both as a machined part and as a casting in a simple manner and because of this method of production can be of a more balanced design. Since, due to the fact that unbalances and other negative influences can be eliminated with this method of manufacture, a piston produced in this manner will also ensure more exactly defined running properties in a cylinder.

By way of example, a description will now be given at an embodiment of the piston shown schematically in the drawings in which: Fig. 1 is a longitudinal centre section through a piston in the plane I-I in Fig. 2; and Fig. 2 is a plan view of a piston according to Fig. 1, but with added details.

Piston 1 is essentially formed by a crown 2 with a ring carrier 3 adjoining it as well as a shell 5 connecting these two parts with a base 4 of the piston. The shell 5 of the piston 1 is constructed as a truncated cone in the form of a solid of revolution which with its base faces the crown 2 and with its truncated cone faces the base 4 of the piston. Attached to this truncated cone of the shell 5 are two legs 6,7 which are symmetrical to a longitudinal plane X extending through the centre of the piston 1 which legs are provided with eyes 8, 9 for a wrist pin 10 shown only schematically in the drawing and by means of which the piston is connected with a guiding member 11.The guiding member 11, which is preferably formed as a ring, in addition to two bearing points 12, 13 for the wrist pin 10 also has a shell 15 which transmits only normal forces onto a cylinder wall 14 of the internal combustion engine with said shell guiding the piston 1 and, in particular its ring carrier 3, on said cylinder wall 14. Thanks to this division of the ring carrier 3, shell 5 with crown 2 on the one hand and the guiding member 14 on the other hand, it is possible to relieve the ring carrier 3 of such normal forces which act obliquely to the cylinder wall 14 so that the ring carrier is better capable of performing its inherent functions with stressing of its sealing and oil control rings 16, 17 being at a lower level.

In order to impart to such a piston 1 the preconditions for a high life expectancy regarding its strength, the shell 5 of the piston 1 is formed not only with the aforementioned conical shape but said shell is supported on the crown 2 of the piston in a manner that the supporting plane 18 facing the crown contacts said crown near the centroid circle 19 of the diameter 20 of the piston. Centroid circle 19 is defined as a pitch circle about the axis of rotation Y of the piston 1 which corresponds substantially to 0.7 times the diameter 20 of the piston. A second supporting plane 21 of the shell 5 near the base 4 of the piston I is in a transverse plane which extends between said shell and the roots of the legs 6,7, i.e. the base of the legs, and is determined by the truncated cone of the piston.This transverse plane extends through the axis of rotation Y whose length 22 corresponds substantially to half the diameter of the centroid circle 19 or the supporting plane 18 of the shell 5 on the crown 2. The supporting faces on the crown 2 and the base 4 of the shell 5 may preferably have the same areas so that they will be loaded uniformly, in particular by the gas pressure, without permitting buckling of the shell 5. In the design of the piston 1 shown here, a combustion chamber 23 is arranged inside the shell 5, said combustion chamber being of spherical shape for the sake of simplicity. Of course, this does not rule out that the piston 1 may also be constructed without the combustion chamber 23 within its shell 5.

In order to control the heat flux from the combustion chamber 23, in this case within the shell 5, to the ring carrier 3 effectively, a ring-shaped constriction 24 is provided near the centroid circle 19 on the crown 2 of piston 1, the ring carrier being connected with the crown through said constriction. As a result of this heat barrier by means of the constriction 24, heat flux from the region of the centre of the combustion space 23 radially outwards is throttled so that the ring carrier 3 is subjected to a much lower level of combustion temperature so that the first sealing ring 16 which is situated nearest to a plane 25 extending through the crown 2 need only be arranged slightly further from the latter than the supporting plane 18 of the shell 5 on crown 2. The constriction 24 between the crown 2 and the ring carrier 3 itself is in the region of the supporting plane 18, in this case in the region of the centroid circle 19, and has a thickness which is less than the distance 26 of the first sealing ring 16 on the ring carrier 3 from said plane 25. In cases where the wall of the shell 5 is comparatively thin, the effective areas of the wall in the supporting planes 18, 21 on the crown 2 and the base 4 of the piston 1 are required to be equal or substantially equal. It is possible also to vary the thickness of the wall of the shell in a manner that the cross-sectional area of this wall on the supporting plane 18 on crown 2 is smaller than the cross-sectional area of this wall of shell 5 on the supporting plane 21 at base 4.The length 27 of the shell 5 itself extends between the two supporting planes 18, 21 and depends on the position of the centroid circle 19 and the ratio of the diameters 20, 22 of the circles extending through said supporting planes 18 and 21.

WHAT WE CLAIM IS: 1. A piston for reciprocating internal combustion engines, typically Diesel engines, with a crown exposed to the heat of the combustion gases and a shell connecting said crown with a guide member transmitting only normal forces as well as a ring carrier connected to the crown of the piston and provided with sealing and oil control rings which ring carrier is connected to the crown of the piston via a constriction situated in the region of a plane containing the crown of the piston and in which piston the shell connecting said crown with said guide member is provided with a base formed by two forkshaped legs at the end opposite to the piston crown which legs are arranged symmetrically to a plane extending through the centre of the piston and provided with eyes for a wrist pin connecting said base with said guide member, wherein the shell of the piston between the crown and the base is constructed as a cone in the shape of a solid of revolution, wherein said cone with the supporting plane at the base of said cone is connected to the crown and a further supporting plane opposite to the crown is connected to the base of the piston and wherein the diameter of the supporting plane at the crown relative to the diameter of the supporting plane at the base is in a ratio of substantially 2:1.

2. A piston as in Claim 1, wherein the supporting plane at the crown of the piston is situated closer to a plane extending through the crown than a sealing point nearest to said plane on the ring carrier of the piston (1).

3. A piston as in Claim 1, wherein the supporting plane on the crown of the piston starts in the region of a constriction situated between the ctrown and the ring carrier and has at least a width corresponding to the cross-sectional area of the shell.

4. A piston as in Claim 1, wherein the cross section of the wall of the shell at the base of the piston is constructed with a greater width than the cross sectional area of the shell at the head of the piston.

5. A piston as in Claim 1, wherein the supporting plane at the base of the piston is provided in the region of the root of the legs starting on the shell.

6. A piston as in Claims 1, 2 and 5, wherein the length of the shell extends from the supporting plane on the crown of the piston to the supporting plane at the base thereof.

7. A piston as in Claim 1, wherein the supporting plane of the shell at the crown is situated in the region of the centroid circle of the crown.

8. A piston as in Claim 2, wherein the seal is formed by a section of the ring carrier situated between the first sealing ring and a plane extending through the crown of the piston.

9. A piston as in Claim 8, wherein this section of the ring carrier is constructed in the form of a truncated cone with its base facing the first sealing ring.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the effective areas of the wall in the supporting planes 18, 21 on the crown 2 and the base 4 of the piston 1 are required to be equal or substantially equal. It is possible also to vary the thickness of the wall of the shell in a manner that the cross-sectional area of this wall on the supporting plane 18 on crown 2 is smaller than the cross-sectional area of this wall of shell 5 on the supporting plane 21 at base 4. The length 27 of the shell 5 itself extends between the two supporting planes 18, 21 and depends on the position of the centroid circle 19 and the ratio of the diameters 20, 22 of the circles extending through said supporting planes 18 and 21. WHAT WE CLAIM IS:

1. A piston for reciprocating internal combustion engines, typically Diesel engines, with a crown exposed to the heat of the combustion gases and a shell connecting said crown with a guide member transmitting only normal forces as well as a ring carrier connected to the crown of the piston and provided with sealing and oil control rings which ring carrier is connected to the crown of the piston via a constriction situated in the region of a plane containing the crown of the piston and in which piston the shell connecting said crown with said guide member is provided with a base formed by two forkshaped legs at the end opposite to the piston crown which legs are arranged symmetrically to a plane extending through the centre of the piston and provided with eyes for a wrist pin connecting said base with said guide member, wherein the shell of the piston between the crown and the base is constructed as a cone in the shape of a solid of revolution, wherein said cone with the supporting plane at the base of said cone is connected to the crown and a further supporting plane opposite to the crown is connected to the base of the piston and wherein the diameter of the supporting plane at the crown relative to the diameter of the supporting plane at the base is in a ratio of substantially 2:1.