DE102012208007A1 - Diesel piston, useful for combustion engine, comprises head that defines dome on its upper side, and metal laminated plastic having layers, which are arranged at portion of dome, where plastic comprises low heat-resistant metal layer - Google Patents

Abstract

The diesel piston comprises a head that defines a dome (70) on its upper side, and a metal laminated plastic having layers, which are arranged at a portion of the dome. The laminated plastic comprises: a low heat-resistant metal layer, which is placed adjacent to the dome; a high heat-resistant metal layer that is arranged at the upper side of a first metal layer; and a cladding, which extends from the dome and defines annular grooves. The piston defines a cylinder-shaped body, which is made of an aluminum-based material. The dome defines a wave-like surface. The diesel piston comprises a head that defines a dome (70) on its upper side, and a metal laminated plastic having layers, which are arranged at a portion of the dome. The laminated plastic comprises: a low heat-resistant metal layer, which is placed adjacent to the dome; a high heat-resistant metal layer that is arranged at the upper side of a first metal layer; and a cladding, which extends from the dome and defines annular grooves. The piston defines a cylinder-shaped body, which is made of an aluminum-based material. The dome defines a wave-like surface. A portion of the wave-like surface defines a combustion bowl (95). The low heat-resistant metal layer comprises the aluminum-based material. The high heat-resistant metal layer comprises a stainless steel-based material. The dome is formed of laminated plastic.

Description

Explanation of related cases

This application is a continuation-in-part of co-pending application No. 13 / 110,947, filed on May 19, 2011, claiming priority to provisional application No. 61 / 390,373, filed October 6, 2010, entitled "Diesel Piston With Bi-Metallic Dome", both of which are owned by the same assignee as the present application and incorporated herein by reference.

Background of the invention

The present invention relates generally to apparatus and methods for casting engine components, and more particularly to a sophisticated bimetallic piston and a way to make the same.

The body of a piston used in internal combustion engines (ICEs) typically consists of a cylindrically shaped head (also referred to as a dome) from which a downwardly extending skirt has one or more annular grooves formed therein and also one or more lands between the grooves having the same radially outward dimension as the outwardly facing surface of the remainder of the shell. Such components are typically made from lightweight materials and with relatively inexpensive molding techniques; According to a preferred form, the pistons are made of a cast aluminum-based alloy. While exposed to high combustion temperatures and pressures during engine operation, increasingly stringent emission and efficiency requirements dictate that future pistons must be built to withstand even more demanding operating conditions. This, in turn, will require the use of materials suitable for higher temperatures and robust designs. This is particularly true of pistons used in diesel engines, which, in addition to being the dominant engine shape for larger commercial vehicles, are increasingly being used to power passenger cars. Similarly, high-speed gasoline engines (such as four-cylinder engines, especially turbocharged engines) have an ever-increasing reliance on hot-burning environments and faster lift components, both of which attempt to simultaneously maximize power output and minimize fuel consumption impose additional burdens on the engine component and material constructions.

While it is expected that all of the various piston components mentioned above will be subjected to additional thermo-mechanical stresses as more power is extracted from smaller structures, it is the dome that is expected to be exposed directly to the combustion process is particularly at risk of damage. Advances in the understanding of combustion dynamics occurring in a chamber created by the piston and cylinder have resulted in more complex shaped piston dome constructions in which alternating regions of pits and bumps result in a wave-shaped dome surface. These improvements in combustion dynamics also hinder the use of lightweight alloys and exacerbate their limited mechanical and thermal utility, with aluminum alloys traditionally used for weight reduction in diesel engine pistons having limited thermal and mechanical durability, making them incompatible with higher temperature requirements more complete (and therefore higher temperature) combustion process. Steel pistons have the ability to withstand the extreme environment; however, they are heavier than aluminum pistons. This weight problem is aggravated by the high rate of speed and acceleration associated with piston movement, which means that the secondary structures may need to be further enhanced with even more detrimental weight control.

Attempts have been made to combine the heat resistance of high temperature resistant materials with the lower weight of aluminum based materials in diesel pistons. However, although composite pistons may meet the above objectives, the difficulties associated with their manufacture have nullified many of their benefits. This is particularly because pistons have long been manufactured as castings with certain machinings or similar changes after casting. As such, it has been difficult to combine the given low cost approach of casting with the flexibility of a custom material arrangement in the piston.

As with the diesel pistons discussed above, the dome of a gasoline engine piston is also exposed to extreme temperatures and, depending on the dome construction (eg, relatively shallow or heavily textured) may have the same type of cracking as a diesel piston with a combustion bowl or with others Be subjected to irregularities of the surface. In addition, the domes are of gasoline engine pistons typically thinner than the pistons of diesel pistons, and therefore more likely to transfer heat very quickly to other areas of the piston - such as the upper annular groove. Such increased exposure increases the need for additional measures in the annular groove, such as anodizing the annular groove or using a high temperature metal insert to provide suitable strength. Cooling approaches can also be used. Oil passages can be used in both diesel and gasoline pistons (particularly in versions of the latter with turbocharging) to cool the annular grooves and other portions of the piston that are exposed to high heat loads. Although features such as annular groove inserts and oil channels provide valuable cooling functions, their incorporation aggravates the cost and complexity of such high performance pistons.

Summary of the invention

One aspect of the invention is a method of manufacturing a diesel piston. In one embodiment, the method includes providing a pattern for the piston that includes a dome; a piston mold is formed around the pattern, the mold comprising a grain material and a binder; that the pattern is removed from the piston mold; that a bimetallic ring is arranged in the piston mold on an upper surface of the dome; that a molten metal is introduced into the piston mold with the bimetallic ring; that the bulb mold is contacted with a solvent for the binder and that the binder and the grain are removed; that the molten metal is cooled; and allowing the molten metal to solidify to form the piston, the bimetallic ring forming at least a portion of the top surface of the dome. In the present context, the bimetal ring may be formed as a laminate of two or more metallic materials, such as a top layer of stainless steel and an aluminum-based backsheet.

Another aspect of the invention is a diesel piston. In one embodiment, the diesel piston includes a body and a dome, wherein at least a portion of an upper surface of the dome comprises a bimetallic ring, the bimetallic ring comprises a first layer of aluminum or an aluminum alloy and a second layer of stainless steel, and wherein the second layer comprises at least one Section of the upper surface of the dome forms, the first layer is connected to the body and the body comprises aluminum or an aluminum alloy.

According to another aspect of the present invention, a piston for an internal combustion engine is disclosed. The dome surface of the piston is covered with a laminate material. Such a piston is preferably formed (like the diesel piston) by casting. The laminate is made of two (or more) layers of a metal to form a covering bimetallic layer or similar structure. The bimetallic features of the laminate are advantageous when joined to the head of the piston because they insulate the lower portions of the piston from excessive heat and impart rigidity and rigidity to the dome. With the addition of the layered piston cover of the present invention, it is possible that such further cooling measures or related measures associated with the high performance diesel and gasoline pistons as mentioned herein may be simplified if not completely eliminated.

Brief description of the drawings

The following detailed description of specific embodiments is best understood when read in conjunction with the following drawings in which like structures are designated by like reference numerals and in which:

1 is a perspective view of a diesel piston with a conventional metallic dome according to the prior art from above;

2 a cutaway view of the diesel piston of 1 is;

3 5 is a cutaway view of a piston according to an aspect of the present invention, wherein at least a flat portion of the dome is formed of a bimetallic material;

4 a gasoline engine version of a piston according to the present invention; and

5 a partial section of 4 shows such that internal features and also the arrangement of the bimetallic laminate are exposed.

Detailed Description of the Preferred Embodiments

An ablation casting lug may be used to make a piston with a molded dome comprising a layered material. The use of ablation casting provides the ability to cast the piston with a near net shape dome without the considerable machining required by other casting techniques. In this way, a bimetallic casting surface can be arranged over at least portions of the piston dome. In a form of the Section include the flat portion of the outer piston circumference to the trough edge. This could be advantageous in that, by limiting the application of the laminate to only a flat landing of the dome, it enhances areas susceptible to high thermal stresses and provides some insulation advantages while keeping weight increases to a minimum.

In one form, a higher temperature resistant layer of stainless steel may be used as one of the laminate layers, while an aluminum based material may serve as another. With such a construction, the low temperature aluminum-based layer would be placed on the dome surface while the more heat-resistant layer (such as the aforementioned stainless steel) would be placed at the top of the first low temperature layer. In addition to the increased resistance to thermal stress relative to the aluminum, the stainless steel of the dome will impart a degree of rigidity and, because of its lower thermal conductivity relative to the underlying aluminum, will act as a thermal barrier which prevents thermal fatigue cracking form the trough edge. The stainless steel material may also provide some degree of isolation of the annular grooves from the heat of combustion.

In a special form of the laminate is designed as a dome insert. The use of a cast insert eliminates the need for laser remelting or tungsten inert gas remelting (TIG remelting), which is typically used to achieve very finely localized fineness.

In another form, a casting process may be used to form the trough itself. In one form, the mold may be made of sand suitable for ablation casting, so that complex dome shapes, including those with reentrant features, can be made easily and inexpensively.

First up 1 and 2 Referring to Figure 1, a conventional diesel piston is 1 shown at the top of the piston 1 in a head (or dome) 10 ends, the a generally flat outer peripheral portion and a recessed central portion 15 having. The downwardly extending side wall has numerous grooves 20 on, which are formed in this and below which a coat 30 towards the bottom of the piston 1 extends, at the a piston pin hole 40 in the piston 1 may be formed to receive a piston pin (not shown). The alloys responsible for the dome 10 of the diesel piston 1 may be prone to early failures, particularly at the top positions along the substantially planar upper portion and also in the recessed central portion 15 , Cracking is particularly prevalent at those locations where temperature regimes and manufacturing constraints may not be sufficient. The features used to increase coolant flow through the piston 1 can be used, oil channels 45 include, through lubricant channels 47 be supplied, as in particular in 2 is shown. Similarly, features used to improve strength may include inserts (such as an insert 23 for the upper annular groove) in one or more of the oil ring grooves 20 are arranged.

Next up 3 Referring to, is a diesel piston 50 according to one aspect of the present invention. A combustion bowl 95 forms a depression or central recessed portion in the upper surface of the dome 70 , In this design, the top surface of the dome 70 in general and the generally flat outer circumference 75 in particular a bimetallic annular laminate 55 include. In one embodiment, the bimetal ring 55 a laminate, which is a lower layer 60 made of aluminum or an aluminum alloy and an upper layer 65 made of a more heat-resistant material such. B. stainless steel includes. In a preferred form, the total thickness of the bimetallic laminate would be from about 4 to about 6 mm, with the aluminum portion accounting for about 10-20% of the total thickness, although other thicknesses and percent aluminum may also be used. According to one form, the laminated ring could 55 be made by pressing. In a further embodiment, the laminated ring could 55 may be formed of a stainless steel ring (about 4 to about 6 mm thick) that could be coated with a thin layer of aluminum (e.g., less than about 100 microns, or more specifically, between about 25 and about 50 microns). It is understood that the laminated ring 55 a substantial entirety of the upper surface of the dome 70 in configurations (not shown) where the waveforms in the top surface are either minimal, slowly rising or (in the case of a substantially planar top surface) non-existent.

According to a preferred manufacturing approach, the laminate 55 with the rest of the piston 70 be poured by the laminate 55 in the form (such as a sand mold) is placed as an insert, wherein a lower layer 60 of the laminate insert 55 The aluminum alloy will be with a low melting point that is metallurgically bonded to the alloy used in the mold to make the dome 70 is used. The thickness of the laminate 55 will be sufficient to ensure that the stainless steel material 65 the edge of the combustion bowl 95 surrounds. Optionally, minor machine edge machining may be performed to provide a more rounded edge for stress concentration reduction. The stainless steel layer 65 not only will provide a thermal advantage as explained above, but also its surface finish should be very good, which additionally minimizes the presence of stress concentration triggers.

The use of the ablation casting process should have a much finer microstructure everywhere with consequent improved properties in the bulb 50 have as a consequence. For example, the faster cooling associated with ablation casting results in finer microstructures and better mechanical properties (as evidenced by a smaller secondary dendrite arm spacing (SDAS)).

As in particular in 3 an ablation casting attachment can be used to force the piston 50 with a dome 70 which has an undercut combustion bowl 95 in the cast state involves manufacture. An optional internal cooling passage 80 (the one oil channel 45 may be substantially similar and may have oil supply passages corresponding to the channels 47 are substantially similar, both in 2 is shown) can also be integrally formed, which depends on the cooling requirements. The ablation uses inorganic (ie, water-soluble) cores, and water is sprayed onto the mold, which slowly flushes away (hence the term "ablation") and rapidly cools the casting. Rapid cooling results in better material properties, and ablation casting, as discussed above, allows the production of complex parts with a fine solidification microstructure. The use of water allows one to control the solidification and cooling of the component separately (eg by applying water to specific areas of the casting before others or by applying different amounts of water to different areas). By providing the high solidification rates and refined microstructure often required to achieve better mechanical properties across the cross-section (such as room temperature and elevated temperature tensile and fatigue properties), ablation casting allows for both complex shapes such as For example, those that combine thin and thick sections as well as those with complex inner cores. The properties across the cross section are superior compared to those made by remelting the trough edge, which provides only the desirable fine microstructure to a depth only slightly below the surface (e.g., a few mm).

The ablation casting method is generally in the U.S. Patent No. 7,121,318 described herein by reference. A pattern is formed of a material and a shape is formed around at least a portion of the pattern. The mold consists of a grain material and a binder. The pattern is removed from the mold, and then a molten metal is introduced into the mold. The mold is contacted with a solvent, and the molten metal is cooled so that it at least partially solidifies to form a casting. The cooling step includes contacting a shell of solidified metal around the molten metal with the solvent.

Other forms of casting are known. For example, note the U.S. Patent No. 7,164,963 . 7 618 823 and 7 225 049 each of which describes analytical method for full-mold casting (a type of ablation casting) and which are incorporated by reference herein. Nevertheless, the present inventors are not aware of any use of this or any other form of ablation casting to form diesel pistons in general and, in particular, diesel pistons with an undercut combustion bowl. The use of ablation casting, as discussed herein, provides the ability to cast the piston with a near net shape dome without the considerable machining required by other methods. Thus, the dome 70 and the combustion bowl 95 to be poured at the same time. In a special form would be the undercut trough 95 and the internal passages (such as the cooling passages 80 ) can be made using a disposable granule that could be made using conventional core technology with retractable tools in the mold. In the present context, the grain shape of the molding medium includes, but is not limited to, silica sand, zirconia sand, chromite sand, ceramic microspheres, or the like.

Advantages associated with the present invention include reduced machining costs, a refined as-cast microstructure for improved mechanical properties, taking advantage of a sand-forming process (or related molding process) to tailor an undercut area (such as those who in 3 in conjunction with the combustion chamber dome 95 shown), to reduce the casting weight and to eliminate the need for an inner salt core. Of the traditional salt core could be replaced by a kernel of the same material as the flask shape.

Improved material yield can be realized by eliminating the large feeders that are often used as part of a mold casting step. Specifically, by using the ablation casting attachment, the inherently high cooling rate may allow the piston 50 which is formed, has a homogeneous microstructure and associated structural properties.

In addition to the finer microstructure and improved plunger properties, the use of the ablation process allows much finer details, including complicated cooling channels, to be poured into the part, such as an oil passage (cooling passage). 80 , The process reduces or eliminates the need for machining after casting in the area around the dome 70 especially around the undercut area of the trough 95 concerns. Since ablation casting is ready for serial production, the transfer to the manufacture of large quantities of pistons or related components is comparatively simple. A disposable grain form could be used to allow the combustion bowl of the piston dome and a lubricating and cooling oil passage to be formed as part of the casting.

The use of ablation casting for the diesel piston 50 is helpful in achieving significant microstructural refinement by reducing or eliminating the need for costly secondary processing, such as B. machining or remelting to achieve. In cases where a refined microstructure is desired, such as. B. at the edge of the trough 95 or other complex 3D areas of the piston 50 , tungsten inert gas remelting (TIG remelting) or laser remelting may be performed locally (in the undercut area of the dome). A subsequent machining, such. B., to obtain a perfect shape of the trough edge can also be reduced or eliminated.

In one form, the invention utilizes the ablation casting process to eliminate the need for large feeders on the piston dome. The ability to cool the dome faster and more uniformly was expected to improve mechanical properties. In particular, the disposable grain shape should allow the combustion bowl 95 is formed in the casting state. Furthermore, the granular material can also be used to seal the oil channel 80 behind the upper annular groove to eliminate the need for a salt core. This also allows rapid prototype production of the piston 50 which can improve general development testing.

Next up 4 and 5 Referring to, is a gasoline version of the piston 100 according to another aspect of the present invention. The gasoline piston 100 includes a dome or a head 110 with a notched area 115 which is essentially an analogue to the trough 95 of the diesel piston 50 is that in 3 and other highly textured contours, surfaces or related shapes formed in the top surface thereof. Although the upper surface of the dome 110 As shown as highly structured, those skilled in the art will appreciate that the present invention is equally applicable to pistons having a simpler (ie, flat) dome surface. The dome 110 also has numerous centrifugal grooves 120 in the downward direction along the substantially cylindrical profile of the piston 100 are formed; these grooves (which individually as ring grooves 122 . 124 and 126 are shown) are used as compression rings and oil rings. As with the diesel piston 50 from 1 to 3 is the topmost ring groove 122 is exposed to the strongest thermal stresses, and therefore may have an annular groove insert (not shown, but substantially similar to the annular groove insert 23 in the diesel piston 50 from 2 shown) for use in situations where the needs of the piston are particularly stringent when carrying loads. Other features, such as oil sprayers (not shown) for cooling the piston 100 , can be used as well.

In this construction, the upper surface of the dome 110 with a bimetallic ring 150 covered as a laminate of aluminum or an aluminum alloy 154 under an alloy 152 made of stainless steel (for example, stainless steel series 300 ) or a related heat-resistant alloy. As in particular in 5 shown can be an oil channel 160 can be used as a possibility, higher combustion temperatures and higher voltages on the piston 100 absorb, wherein such channels can be cast. The incorporation of the bimetallic laminate 150 helps with the piston 100 preferably by reducing the size or complexity of such channels, ring inserts or sprayers, or preferably by eliminating such channels, ring inserts or sprayers in their entirety.

As explained above, the highly structured or contoured nature of the head is due 110 on ways that the shaping can optimize the combustion process, with the notched area 115 can form a combustion bowl, which coincides with the most active region of the combustion profile. Although both the diesel piston 50 as well as the gasoline piston 100 theoretically with three rings 20 . 120 are shown in the the corresponding heads are formed, it will be appreciated that a smaller or larger number of such rings may be present, especially in the diesel piston 50 in which up to five rings can be used. The coat 130 extends downwards from the head 110 and has a piston pin hole 140 to receive a piston pin (not shown) coupled to a connecting rod and a crankshaft (none of which is shown).

According to one form, the bimetallic laminate becomes 150 either pressed into a flat disc after casting and then machined to the final dome shape or cast directly into the dome shape, the machining being limited to the removal of an aluminum burr to expose the laminate.

The relatively low thermal conductivity of the stainless steel layer 152 Insulates the upper ring groove 122 and other critical areas, possibly reducing the need for inserts, channels (eg, the oil gallery 160 ) and is eliminated by spraying devices. The construction of the piston (its mass) can even at the addition of the stainless steel layer 152 be optimized.

The piston 100 that with the bimetallic laminate 150 Cast in the dome surfaces can be prepared by any of various casting methods, which include the ablation method mentioned above, and also by permanent mold casting and casting using lost moldings. The chill casting process or die casting process using lost moldings - which are more typical for high volume piston production - can also be used when the laminate material (ie, the bimetallic material) enters the dome 110 of the piston 100 is involved. The laminate material 150 is fixed in the mold tool prior to metal injection, and the final shape of the dome 110 is achieved by machining to the surface of the laminate material 150 expose. Thus, the properties and microstructures for current production pistons are typical. Important issues to consider include (a) positioning of the bimetallic laminate material 150 in the mold so that the shape is correctly aligned and the stainless steel layer 152 on the exposed surface of the dome 110 lies; (b) the use of a portion of the bimetallic material 150 thick enough to machine (clean) the surface of the dome 110 to remove excess cast aluminum and expose the stainless steel with the correct final shaping details; and (c) using a nondestructive inspection method to evaluate the degree of bonding between the aluminum side of the bimetallic material and the surface of the cast aluminum alloy.

It should be understood that terms such as "preferred," "typical," and "typically" are not used herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the invention claimed invention. Rather, these terms are intended merely to highlight alternative or additional features that may or may not be used in a particular embodiment of the present invention. It should be understood that in order to describe and define the present invention, the term "device" is used herein to represent a combination of components and individual components regardless of whether the components are combined with other components. Similarly, the term "substantially" is used herein to represent the natural level of uncertainty that may be associated with any quantitative comparison, value, quantitative measurement, or other representation. The term "substantially" is also used herein to represent the degree to which a quantitative representation may differ from a given reference without causing a change in the basic function of the subject under consideration.

While certain representative embodiments and details have been shown to illustrate the invention, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention as defined in the appended claims.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7121318 [0025]
• US 7164963 [0026]
• US 7618823 [0026]
• US 7225049 [0026]

Claims (10)

Piston for an internal combustion engine, wherein the piston defines a substantially cylindrical body and comprises: a head defining a dome at the top thereof; a multilayer metal laminate disposed on at least a portion of the dome, the laminate comprising a less refractory metal layer adjacent to the dome and a more refractory metal layer disposed on top of the first metal layer, and a jacket extending away from the dome and defining at least one annular groove formed therein. Piston according to claim 1, wherein the body is made of an aluminum-based material. The piston of claim 1, wherein the dome defines a wavy surface. The piston of claim 3, wherein at least a portion of the undulating surface defines a combustion bowl. The piston of claim 1, wherein the less heat-resistant metal layer comprises an aluminum-based material. The piston of claim 5, wherein the refractory metal layer comprises a stainless steel based material. Piston according to claim 1, wherein the at least one annular groove comprises a plurality of annular grooves, at least one of which is free from a Ringnuteinsatz. A piston according to claim 1, wherein the body is free of an oil passage formed therein. A piston according to claim 1, wherein the laminate is formed on a substantial entirety of the dome. Piston according to claim 1, wherein the piston is designed as a gasoline engine piston.

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