Patent Publication Number: US-2019178202-A1

Title: Piston Consisting Of An Inner Part And An Outer Part

Description:
FIELD OF INVENTION 
     The invention relates to a piston of an internal combustion engine and to a method for producing a piston of this kind in accordance with the features of the respective preambles of the two independent patent claims. 
     The invention relates to a novel design for a piston of an internal combustion engine. 
     BACKGROUND 
     Pistons for internal combustion engines are produced in one piece, e.g. by casting. Moreover, there is a known practice of producing ready-to-use one-piece pistons by manufacturing a top part and a bottom part and joining them non-detachably in a horizontal plane. 
     A piston which has a ring groove region, a piston skirt and a piston boss for receiving a piston pin, wherein the piston is formed by two parts, which are produced separately from each other and are joined together non-detachably to form the one-piece piston, is known from DE 10 2016 116 046 A1. 
     The plane in which the top part and the bottom part are joined together non-detachably is horizontal, i.e. transverse with respect to a piston stroke axis of the piston. 
     SUMMARY 
     It is the underlying object of the invention to specify a novel design for a piston of an internal combustion engine and a corresponding production method. 
     In respect of the piston, it is envisaged according to the invention that the piston is formed by an outer part, which includes the ring groove region and the piston skirt and into which is inserted (more particularly concentrically with respect to the piston stroke axis) an inner part, which includes the piston bosses and the pin bores, wherein the two parts are joined together non-detachably in at least one vertical plane. By virtue of the vertical alignment of the joining plane, the stresses acting on the piston, in particular tensile and compression forces during combustion, can be absorbed and transmitted significantly better than is the case with a horizontal joining plane. Moreover, greater geometrical degrees of freedom are available in the configuration of the two parts since large areas of the two parts, which have to be produced or machined, are significantly more accessible than in the case of two parts which are produced separately from each other and are joined in a horizontal plane. The two mutually opposite piston bosses with their respective pin bores are thus at least partially, in particular completely, surrounded by the piston skirt of the outer part. In this case, the piston skirt has an aperture, preferably two opposite apertures, via which the piston pin can be inserted into the pin bores in order thereby to connect the piston rod to the piston. Instead of a very largely or completely cylindrical piston skirt (with at least one aperture for installing the piston pin), it is also possible to consider loadbearing skirt wall sections which extend from an upper region of the outer part to the lower end thereof (which can simultaneously also be the lower end of the piston). 
     The two parts can consist of the same material or of different materials. The same applies to the production methods for these. The two parts can likewise be of symmetrical design with respect to the piston axis, but do not have to be. 
     In a special embodiment, the two ends of the two parts (outer and inner part) forming the piston extend from the upper end of the piston (which faces the combustion chamber), to the lower end thereof (which faces the crankcase). The outer part is not designed as a ring element known per se, which is arranged and secured around the inner part only in the upper region of the piston (above an oil scraper ring or above the ring groove region per se). 
     As a development of the invention, provision is made in principle for the piston to have a cooling duct, wherein, in this case, the alternatives envisaged are either that the cooling duct is formed exclusively by the inner part, that the cooling duct is formed exclusively by the outer part or that the inner and the outer part are configured in such a way that the cooling duct is formed after they are joined together. In the last-mentioned case, this means that both the inner and the outer part contribute to the formation of the cooling duct, to be more precise the walls thereof. 
     As a development of the invention, it is envisaged that at least one joint, preferably an encircling joint, between the two parts is formed by these two parts and has mutually corresponding geometries, wherein the geometries are chosen so that, when the inner part is inserted into the outer part, positive engagement arises in the region of the joint. There is no need for a further joining operation, e.g. welding or brazing or the like, since the two parts are connected positively to one another by a suitable joining method. However, a materially integral joining method can optionally be performed in addition. 
     In respect of the method for producing a piston, it is envisaged according to the invention that the piston is formed by an outer part, which includes the ring groove region and the piston skirt and into which is inserted (more particularly concentrically with respect to the piston stroke axis) an inner part, which includes the piston bosses and the pin bores, wherein the two parts are then joined together non-detachably in a vertical plane. 
     Thus, according to the invention, a novel alignment of the at least one joining plane and the configuration of the two parts which form the finished piston after being joined together is available, in which the same advantages apply as have already been described above with respect to the piston itself. 
     Given this situation, the underlying concept of the invention is no longer to form the at least one parting plane horizontally but to form it substantially vertically. 
     An outer, approximately cylindrical part is produced, into which an inner part is inserted (more particularly concentrically with respect to the piston stroke axis), fixed in its position and connected non-detachably to the outer part. 
     The outer, approximately cylindrical part has essential piston elements, such as a ring groove region, a piston skirt and the like. 
     The inner part likewise has essential elements of the piston, e.g. a combustion chamber recess but especially the piston bosses with the pin bore situated therein. 
     In the upper region of the two parts, which is associated with the combustion chamber of the internal combustion engine, said parts can have geometries which form an encircling annular cooling duct, either in isolation or, as an alternative, together after joining. The geometries in the outer and/or inner part which form the cooling duct are freely accessible for machining, and therefore any shapes, even relatively complex ones, can be implemented for the cooling duct. 
     Many different possibilities are available for joining the inner part non-detachably to the outer part. Any nonpositive and/or positive as well as any materially integral joining method may be considered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of one example of a piston of the present invention. 
         FIG. 2  is an alternate cross-sectional view of the piston shown in  FIG. 1 . 
         FIG. 3  is a perspective view of an example of a piston outer part of the present invention. 
         FIG. 4  is a perspective view of an example of a piston inner part of the present invention. 
         FIGS. 5-10  are partial cross-sectional views of alternate configurations in the region of a joint between exemplary piston inner parts and outer parts. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative embodiment of a piston  1  according to the invention is illustrated in  FIGS. 1 and 2  in two different views. This piston  1  has an outer, substantially cylindrical outer part  2 , into which an inner part  3  is inserted and moved into the desired position thereof in relation to the outer part  2 . 
     After the insertion of the inner part  3  into the outer part  2 , the two parts  2 ,  3  are connected to each other at at least one joint, ensuring that relative movement between these two parts  2 ,  3  is no longer possible. It is conceivable to have just one joint, preferably an encircling joint. In a particularly advantageous way, the two parts  2 ,  3  are connected to each other by two joints V 1 , V 2 , which are preferably both of encircling configuration and which are situated in different planes. Moreover, the alignment of the at least one joint V 1 , V 2  is no longer horizontal but vertical. The manner in which the two parts  2 ,  3  are connected to each other at the joints V 1 , V 2  can be the same or, as an alternative, can be different. 
     Otherwise, the two parts  2 ,  3  are configured in such a way that they form conventional piston elements such as a ring groove region  4 , a combustion chamber recess  5 , a cooling duct  6 , a piston skirt  7 , piston bosses  8  with pin bores  9  and, if appropriate, further piston elements. 
       10  denotes a piston stroke axis and  11  denotes a pin axis. 
     In  FIGS. 3 and 4 , the two parts  2 ,  3  are illustrated once again in isolation before being inserted one into the other.  FIG. 3  shows the outer part  2 , wherein it can be seen that said part is formed substantially in a cylinder shape. It is preferably cast or forged, although other production methods are not excluded. 
       FIG. 4  shows the inner part  3 , which can likewise be obtained in any suitable production method, e.g. casting, forging or the like. 
     When considering  FIGS. 3 and 4 , it should be noted that gaps or through bores  7 A are formed in the outer part  2  in those regions in which the piston bosses  8  with the pin bores  9  thereof are located in the inner part  3  in order to allow access for the installation of the pin in the pin bores  9 . 
       FIGS. 5 to 10  show various illustrative geometries in the region of the joint V 1  between the two parts  2 ,  3 . In particular, the geometries shown are chosen in such a way that, when the inner part  3  is inserted into the outer part  2 , positive engagement arises in the region of the joint V 1 , and therefore a further joining operation, e.g. welding or brazing or the like, is required. The materially integral connection of the two parts  2 ,  3  then takes place only in the region of the joint V 1  and/or V 2 , where the non-detachable connection is accomplished by means of brazing, welding, adhesive bonding or the like. Conversely, it is likewise conceivable for the joint V 1  and/or V 2  to be configured geometrically in such a way that no positive engagement but only materially integral connection by means of brazing, welding, adhesive bonding or the like is possible. 
     Depending on the embodiment of the geometries of the two parts  2 ,  3  in the region of the at least one joint, in particular in the region of both joints, in particular in the region of both joints V 1 , V 2 , identical joining methods, e.g. the abovementioned welding, brazing or adhesive bonding, but also shrink-fitting or the like, may be considered. However, this is not absolutely necessary, and therefore different non-detachable joining methods are also possible in the region of the at least one, preferably in the region of both, joints V 1 , V 2 . 
     The geometries in the region of joint V 1  which are alternately shown in  FIGS. 5 to 10  have the advantage that the outer part  2  can be supported on the inner part  3  and vice versa during the upward and downward movement of the piston  1  along the piston stroke axis  10 . 
     Overall, the novel configuration of a piston of this kind results in a reduction in the use of material, and therefore the weight of the blank can be reduced. Moreover, more economical production as compared with known pistons can be achieved, wherein, by virtue of the shaping of the two parts  2 ,  3 , all regions of the blank parts which initially form the two parts  2 ,  3  are readily accessible for corresponding machining. 
     It is self-evident that the piston  1  is finish-machined and adjusted to size when the two parts  2 ,  3  are arranged in position relative to one another and are non-detachably connected. This applies especially to the spacings of joining beads if these are formed and are troublesome. 
     LIST OF REFERENCE SIGNS 
       1 . piston 
       2 . outer part 
       3 . inner part 
       4 . ring groove region 
       5 . combustion chamber recess 
       6 . cooling duct 
       7 . piston skirt 
       8 . piston boss 
       9 . pin bore 
       10 . piston stroke axis 
       11 . pin axis