CA1078274A - Insulated composite piston - Google Patents
Insulated composite pistonInfo
- Publication number
- CA1078274A CA1078274A CA294,075A CA294075A CA1078274A CA 1078274 A CA1078274 A CA 1078274A CA 294075 A CA294075 A CA 294075A CA 1078274 A CA1078274 A CA 1078274A
- Authority
- CA
- Canada
- Prior art keywords
- crown
- piston
- piston body
- discs
- bolt
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
- F02F7/00—Casings, e.g. crankcases
- F02F7/0085—Materials for constructing engines or their parts
- F02F7/0087—Ceramic materials
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
- F02F3/00—Pistons
- F02F3/0015—Multi-part pistons
- F02F3/0023—Multi-part pistons the parts being bolted or screwed together
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
- F02F3/00—Pistons
- F02F3/10—Pistons having surface coverings
- F02F3/12—Pistons having surface coverings on piston heads
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16J—PISTONS; CYLINDERS; SEALINGS
- F16J1/00—Pistons; Trunk pistons; Plungers
- F16J1/005—Pistons; Trunk pistons; Plungers obtained by assembling several pieces
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B3/00—Engines characterised by air compression and subsequent fuel addition
- F02B3/06—Engines characterised by air compression and subsequent fuel addition with compression ignition
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
- F05C2201/00—Metals
- F05C2201/02—Light metals
- F05C2201/021—Aluminium
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
- F05C2201/00—Metals
- F05C2201/04—Heavy metals
- F05C2201/0433—Iron group; Ferrous alloys, e.g. steel
- F05C2201/0448—Steel
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
- F05C2251/00—Material properties
- F05C2251/04—Thermal properties
- F05C2251/042—Expansivity
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- Ceramic Engineering (AREA)
- Pistons, Piston Rings, And Cylinders (AREA)
- Cylinder Crankcases Of Internal Combustion Engines (AREA)
Abstract
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ABSTRACT
The disclosure illustrates an insulated composite piston comprising a crown of ceramic or other heat resistant material secured to an aluminum piston body by a bolt of temperature resistant alloy. A low conductivity interface between the crown and the body is provided by a series of stacked discs having low effective thermal conductivity.
The relative thermal expansion of the parts is compensated for by bellville washers on the bolt. The above arrangement insulates the crown from the piston body thereby minimizing the temperature gradient across the crown so that its temperature can be maintained as high as necessary to increase efficiency and minimize noxious emissions.
ABSTRACT
The disclosure illustrates an insulated composite piston comprising a crown of ceramic or other heat resistant material secured to an aluminum piston body by a bolt of temperature resistant alloy. A low conductivity interface between the crown and the body is provided by a series of stacked discs having low effective thermal conductivity.
The relative thermal expansion of the parts is compensated for by bellville washers on the bolt. The above arrangement insulates the crown from the piston body thereby minimizing the temperature gradient across the crown so that its temperature can be maintained as high as necessary to increase efficiency and minimize noxious emissions.
Description
10'7~274 ' In the internal combustion engine art and particularly that portion dealing with diesel engines, the insulated combustion chamber has been proposed to increase efficiency and minimize pollutants. Efficiency is increased because the amount of combustion heat rejected to the engine cooling system is minimized. Furthermore, the existing temperature available to drive the turbine of a turbocharged engine is greatly increased.
Past attempts at insulating the combustion chamber may be separated into a number of broad categories. The first is where surfaces of the combustion chamber are sprayed with a ceramic insulating material. These surfaces would include the piston crown, the cylinder head and possibly the walls of the cylinder. The difficulty with this approach is maintaining the integrity of the layer because of the t stresses of the combustion cycle and the problems of thermal expansion.
Another approach has been to make one or more of the components which define the combustion chamber out of insulating material. Alternatively one may utilize a ceramic insert of substantial thickness in one of these components.
Problems arise with devices of this type because they are exposed on one side to the hot combustion gases and on the other side by the cooler supporting structure around the combustion chamber. As such, rather substantial temperature gradients (as high as 1200F) may exist across these materials.
Excessive thermal stresses and distortion will result if the part is made from material other than ultra low thermal expansion material.
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, ~ 1078~74 The above problems are solved by a piston having an annular crown of temperature resistant material positioned ~! over a corresponding piston body. The crown and piston body - are secured together and the interface between them is , provided with means having a relatively low overall conductivity so that the temperature gradient across the crown is minimized.
According to the invention there is provided a piston for an internal combustion engine having a generally , annular crown portion of temperature resistant material with the crown portion having a circular periphery. The crown portion is located so that both it and the generally annular piston body having a circular periphery have opposed planar surfaces. A plurality of stacked discs having a relatively low conductivity planar interface between adjacent discs are positioned between the opposed planar surfaces of the crown and , piston body for forming a low effective thermal conductivity t~ interface. The planar surface of the crown extends radially ' outward at least as far as the periphery of the discs. Further included is a means for fastening the crown portion to the piston body so that the temperature gradient across the crown is minimized.
Advantageously the crown and piston body have aligned holes with the one in the piston body terminating in an interior recess thereof. The fastening means is comprised of a bolt extending through the latter mentioned holes having a head positioned on the crown and a threaded portion extending through the piston body to the interior recess. A nut threaded onto the end of the bolt acts on a means positioned between the nut and the piston body for yieldably urging the piston body and crown towards one another. The latter urging means may ~ - 2 -` 107827~
..
comprise a spring means positioned around the bolt and acting against the nut and the piston body, the spring means comprising a plurality of belleville washers.
Preferably the discs do not extend to the periphery of the interface between the crown and the piston body being of an overall thickness so that the crown and piston body are maintained out of contact with one another by utilizing an annular recess in the piston body so that compressive loads on the crown are transmitted to the latter across an annular area with the radius of the annular recess being approximately equal to the difference in radius between the crown and the outer periphery of the discs, a uniform bending load being imposed upon the crown by compressive forces.
The above and other features of the invention will be apparent from a reading of the following description of the disclosure shown in the accompanying drawings and the novelty thereof pointed out in the appended claims.
Figure 1 is a longitudinal view, partially sectioned, illustrating a piston which embodies the present invention.
,~ 20 Figure 2 is a fragmentary longitudinal view of a piston incorporating an alternate embodiment of the present invention.
Referring to figure 1 there is shown a piston 10 comprising a generally annular body portion 12 having a ring band ~ .
section 14 formed around its circular periphery. The ring band , section 14 includes a plurality of circumferential grooves 16 which receive compression and oil rings 15, 17 respectively.
The piston rings 15, 17 seat against a bore 19 which terminates to form a combustion chamber 21.
' 30 The piston 10 is reciprocable in the bore 19. The piston body has wrist pin bosses 18 with aligned bores 23 - 2a -I~
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adapted to receive a wrist pin which permits the piston body to be connected to a connecting rod (both elements are not shown). In an internal combustion engine the connecting . rod is journaled on a crankshaft to provide a rotary output.
- 2b -.
^' 107~3Z7 . i .
The piston 10 is shown as a cross head type piston jlwhich incorporat~s a separate skirt assembly connected to i,the piston body through the wrist pin. Although a skirt is , l¦necessary to successfully utili~e the piston in an internal 51icombustion engine, a specific description will be omitted in order to simplify the description of the present invention.
I It should be apparent to those skilled in the art that skirt j~sections may also be formed integrally with the piston body :''' ' 112.
10 I The piston also includes a crown portion 20 positioned ~ ~over the upper surfaoe 22 of piston body 12. Crown 20 has a s - ¦circular periphery and an upper face 2~ exposed to the combustion l ¦~ chamber 21 which has a "Mexican hat" configuration for I~efficient combustion. The configuration of upper face 24, 15!l however, need not be limited to this specific type. The Icrown 20 may be formed from any one of a number of heat ,~ resistant materials. Examples of such materials are ceramics , such as silicon nitride (Si3N4), lithia alumina sillca i! (LAS), fused silica (SiO2) and silicon carbide (SiC), reaction 20~l sintered silicon carbide (RSS:C) sintered silicon carbide (SSic), and reaction bonded silicon nitride (RBSN). Any one I of these materials can withstand temperature levels experienced ~i ! in the combus-tion chamber. However, the construction shown Il below permits all of the above to be used successfully in 251l spite of some oth~r properties such as high thermal coefficient il and thermal expansion.
~ltcrnatively crown 20 may be formed from a heat ! resistant metal. Examples of such a material are stainless .. Il . l . I' , 1' , .
il steel or coated more common steels. These materiais do not ¦ have as high a temperature capability as the ceramics in Il that their temperature capability is approximately 1400-: ¦! 16000 F (760-8700 C) compared to about 22000 F (12000 C) , 5 ¦I for ceramics. However, their temperature resistance is - i still high enough to permit an increase in combustion I efficiency. In addltion they are more readily adaptable to - mass production.
The crown 20 and the piston body 12 each have coaxial holes 26 and 28 respectively. A bolt 30 having a ; head 32 received in recess 34 in crown 20 has a shank 36 extending through holes 26 and 28. Preferably, the head 32 of bolt 30 is shaped to form an extension of the upper face -¦ 24 of crown 20. In addition, bolt 32 is formed from a high lS¦1 temperature, high strength alloy, generally of a nickel or ¦1 cobalt base. Examples of such alloys are Udimet 700, i, nlmonic 115 or 90, R-41, or Waspalloy.
The shank 36 of bolt 30 terminates in a threaded . I . .
portion of 38 received in a recess 40 formed in the interior 20 ~ of piston body 12. Recess 40 has a shoulder 42. The flange j! 44 of a sleeve-like spacer 46 abuts shoulder 42. A nut 48 ii is threaded over the end of bolt 30. ~ spring assembly 50 ,j .
acts against nut 48 and the inner wall of a recess 52 in ,¦ spacer 46 to hold the crown 20 and piston body 12 together 25 1I while permitting differential thermal e~pansion- As illustrated, ; li the spring assembly 50 comprises a plurality of stacked belleville washcrs which arc wclL krlowrl compact spring assemblies.
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782~74 ~!
,'` ilj , I
., ., i prime feature of the present invention is the : ~I provision of an interface between crown 20 and piston body 12, generally designated as 54 which has a low effective . I
~~ thermal conductivity. As shown in figure 1, the interface 54 may ; 5 ¦I comprise a plurality of ~ubstantially Planar discs 56 sandwiched jl, between the lower planar surface 58 of crown 20 and the Planar floor of an annular recess 60 in the top of piston body 12.
~, Each of the discs 56 has a central opening 62 receiving the shank 36 of bolt 30. The discs 56 are selected so that the effective thermal conductivity across the interface between ¦ adjacent discs is relatively low. A low effective thermal conductivity may be achieved with commonly available material .
il by using steel washers having roughened surfaces, for example, " a surface roughness of 200~ in. It has been found that , ordinary steel washers with no special roughening of their l surface provide an overall low effective thermal conductivity.
; l, The stacked discs are extremely effective in ' producing a low thermal conductivity. Heat transfer coefficients i!on the order of 0.5 BTU/~IR-FT- F are achievable compared to 20 ~180 BTU/HR-FT- F for a solid piston body-crown interface.
' It should be noted also that a greater or lesser number of ,'discs may be employed to achieve a greater or lesser thermal conductivity. Since the diameter of the discs 56 does not 'extend to the peripl-ery of the crown 20 or piston body 12, 25 ',-their thickness ib sclected so that the portion of the crown ~i20 outside of these discs 56 is out of contact with the 22 ' of piston body 12.
i , Furthermore, the discs 56 support crown 20 over a l' relatively broad annular planar area defined at its inner ¦, diameter by the diameter of hole 28 and at its outer diameter I by the diameter of discs 56. This area of contact minimizes 5 ¦i the unit pressure on the discs 56 for a given pressure in ¦~ combustion chamber 21 and therefore contributes to a low ;-¦¦ thermal conductivity across the interface between adjacent jl discs. The annular contact area divides the radius of crown-j 20 into approximately equal sections. It can be seen that 0~¦ the radial dimension of crown 20 between hole 26 and a point ¦i in line with the wall of hole 28 is approximately equal to the radial dimension between the periphery of discs 56 and the outer periphery of crown 20. The bendiny loads on the ll top of crown 20 due to combustion pressures are therefore lslJ equalized.
¦' The discs 56 shown in figure 1 constitute one way ll of insulating crown pis~on body 12. Figure 2 shows an 'i alternate form of interface 54' which uses a disc 64 which . .
Ij has a relatively low conduc-tivity. This disc 64 may be 20', formed of porous metal or of steel wool compressed sufficiently to resist compressive loads. In certain instances it may be also advantageous to use a plurality of discs 64.
With any of the interface materials described ,l above, the crown 20 is effectively insulated from the piston 25 i body 12, u5ually formed of high conductivity aluminum. This , insulation provides a primary advantage of minimizing the thermal gradient between the upper and lower surfaces 24 and 58 of crown 20. As such internal thermal stresses are ', substantially minimized. This permits the material selection ii ' - 6 -I
: - I -, , . .
1l .
jjfor crown 20 to be very flexible since the material only must be able to withstand combustion temperatures and resist moderate compressive loads. The temperature gradient for ¦ithe most part is taken up by the interface 54 between the ' 5l,~crown 20'and piston body 12. Since the only load on it is~a ilcompressive one, the thermal stress caused by the temperatur.e j~gradient is not as detrimental as it would be if it occurred , !l , . .
'in the,crown 20. With the plurality of discs,~the gradient is distributed over a plurality of interfaces thereby mini'mizing 101 the stresses on the individual elements.
~' i ~ Any varia~tions in thermal expansion which occur between the piston body, interface 54 and crown 20 are compensated for by the spring assembly 50 to assure a relatively l!uniform compressive loading holding the parts together.
15 1l Since the shoulder 42 is larger in area than that available on the body 12,-for receiving the spring assembly S0, spacer ' I element 46,assures a greatly improved seat for carrying the : j;joint load on the body ].2. , 1', The above piston achieves the objec'tives of a well 20i~insulated combustion chamber to increase efficiency and to reduce emissions. 'Furthermore it does so with an economlcal, , , .
, ,.effective construction that permits ready replacement of the : ' parts.
!
. .
Past attempts at insulating the combustion chamber may be separated into a number of broad categories. The first is where surfaces of the combustion chamber are sprayed with a ceramic insulating material. These surfaces would include the piston crown, the cylinder head and possibly the walls of the cylinder. The difficulty with this approach is maintaining the integrity of the layer because of the t stresses of the combustion cycle and the problems of thermal expansion.
Another approach has been to make one or more of the components which define the combustion chamber out of insulating material. Alternatively one may utilize a ceramic insert of substantial thickness in one of these components.
Problems arise with devices of this type because they are exposed on one side to the hot combustion gases and on the other side by the cooler supporting structure around the combustion chamber. As such, rather substantial temperature gradients (as high as 1200F) may exist across these materials.
Excessive thermal stresses and distortion will result if the part is made from material other than ultra low thermal expansion material.
q~
~ ,~ ,., . .
, ~ 1078~74 The above problems are solved by a piston having an annular crown of temperature resistant material positioned ~! over a corresponding piston body. The crown and piston body - are secured together and the interface between them is , provided with means having a relatively low overall conductivity so that the temperature gradient across the crown is minimized.
According to the invention there is provided a piston for an internal combustion engine having a generally , annular crown portion of temperature resistant material with the crown portion having a circular periphery. The crown portion is located so that both it and the generally annular piston body having a circular periphery have opposed planar surfaces. A plurality of stacked discs having a relatively low conductivity planar interface between adjacent discs are positioned between the opposed planar surfaces of the crown and , piston body for forming a low effective thermal conductivity t~ interface. The planar surface of the crown extends radially ' outward at least as far as the periphery of the discs. Further included is a means for fastening the crown portion to the piston body so that the temperature gradient across the crown is minimized.
Advantageously the crown and piston body have aligned holes with the one in the piston body terminating in an interior recess thereof. The fastening means is comprised of a bolt extending through the latter mentioned holes having a head positioned on the crown and a threaded portion extending through the piston body to the interior recess. A nut threaded onto the end of the bolt acts on a means positioned between the nut and the piston body for yieldably urging the piston body and crown towards one another. The latter urging means may ~ - 2 -` 107827~
..
comprise a spring means positioned around the bolt and acting against the nut and the piston body, the spring means comprising a plurality of belleville washers.
Preferably the discs do not extend to the periphery of the interface between the crown and the piston body being of an overall thickness so that the crown and piston body are maintained out of contact with one another by utilizing an annular recess in the piston body so that compressive loads on the crown are transmitted to the latter across an annular area with the radius of the annular recess being approximately equal to the difference in radius between the crown and the outer periphery of the discs, a uniform bending load being imposed upon the crown by compressive forces.
The above and other features of the invention will be apparent from a reading of the following description of the disclosure shown in the accompanying drawings and the novelty thereof pointed out in the appended claims.
Figure 1 is a longitudinal view, partially sectioned, illustrating a piston which embodies the present invention.
,~ 20 Figure 2 is a fragmentary longitudinal view of a piston incorporating an alternate embodiment of the present invention.
Referring to figure 1 there is shown a piston 10 comprising a generally annular body portion 12 having a ring band ~ .
section 14 formed around its circular periphery. The ring band , section 14 includes a plurality of circumferential grooves 16 which receive compression and oil rings 15, 17 respectively.
The piston rings 15, 17 seat against a bore 19 which terminates to form a combustion chamber 21.
' 30 The piston 10 is reciprocable in the bore 19. The piston body has wrist pin bosses 18 with aligned bores 23 - 2a -I~
107~3Z7~
```
adapted to receive a wrist pin which permits the piston body to be connected to a connecting rod (both elements are not shown). In an internal combustion engine the connecting . rod is journaled on a crankshaft to provide a rotary output.
- 2b -.
^' 107~3Z7 . i .
The piston 10 is shown as a cross head type piston jlwhich incorporat~s a separate skirt assembly connected to i,the piston body through the wrist pin. Although a skirt is , l¦necessary to successfully utili~e the piston in an internal 51icombustion engine, a specific description will be omitted in order to simplify the description of the present invention.
I It should be apparent to those skilled in the art that skirt j~sections may also be formed integrally with the piston body :''' ' 112.
10 I The piston also includes a crown portion 20 positioned ~ ~over the upper surfaoe 22 of piston body 12. Crown 20 has a s - ¦circular periphery and an upper face 2~ exposed to the combustion l ¦~ chamber 21 which has a "Mexican hat" configuration for I~efficient combustion. The configuration of upper face 24, 15!l however, need not be limited to this specific type. The Icrown 20 may be formed from any one of a number of heat ,~ resistant materials. Examples of such materials are ceramics , such as silicon nitride (Si3N4), lithia alumina sillca i! (LAS), fused silica (SiO2) and silicon carbide (SiC), reaction 20~l sintered silicon carbide (RSS:C) sintered silicon carbide (SSic), and reaction bonded silicon nitride (RBSN). Any one I of these materials can withstand temperature levels experienced ~i ! in the combus-tion chamber. However, the construction shown Il below permits all of the above to be used successfully in 251l spite of some oth~r properties such as high thermal coefficient il and thermal expansion.
~ltcrnatively crown 20 may be formed from a heat ! resistant metal. Examples of such a material are stainless .. Il . l . I' , 1' , .
il steel or coated more common steels. These materiais do not ¦ have as high a temperature capability as the ceramics in Il that their temperature capability is approximately 1400-: ¦! 16000 F (760-8700 C) compared to about 22000 F (12000 C) , 5 ¦I for ceramics. However, their temperature resistance is - i still high enough to permit an increase in combustion I efficiency. In addltion they are more readily adaptable to - mass production.
The crown 20 and the piston body 12 each have coaxial holes 26 and 28 respectively. A bolt 30 having a ; head 32 received in recess 34 in crown 20 has a shank 36 extending through holes 26 and 28. Preferably, the head 32 of bolt 30 is shaped to form an extension of the upper face -¦ 24 of crown 20. In addition, bolt 32 is formed from a high lS¦1 temperature, high strength alloy, generally of a nickel or ¦1 cobalt base. Examples of such alloys are Udimet 700, i, nlmonic 115 or 90, R-41, or Waspalloy.
The shank 36 of bolt 30 terminates in a threaded . I . .
portion of 38 received in a recess 40 formed in the interior 20 ~ of piston body 12. Recess 40 has a shoulder 42. The flange j! 44 of a sleeve-like spacer 46 abuts shoulder 42. A nut 48 ii is threaded over the end of bolt 30. ~ spring assembly 50 ,j .
acts against nut 48 and the inner wall of a recess 52 in ,¦ spacer 46 to hold the crown 20 and piston body 12 together 25 1I while permitting differential thermal e~pansion- As illustrated, ; li the spring assembly 50 comprises a plurality of stacked belleville washcrs which arc wclL krlowrl compact spring assemblies.
'~ ' .
l - 4 -e .. .. I
~ !
,` i ! .
782~74 ~!
,'` ilj , I
., ., i prime feature of the present invention is the : ~I provision of an interface between crown 20 and piston body 12, generally designated as 54 which has a low effective . I
~~ thermal conductivity. As shown in figure 1, the interface 54 may ; 5 ¦I comprise a plurality of ~ubstantially Planar discs 56 sandwiched jl, between the lower planar surface 58 of crown 20 and the Planar floor of an annular recess 60 in the top of piston body 12.
~, Each of the discs 56 has a central opening 62 receiving the shank 36 of bolt 30. The discs 56 are selected so that the effective thermal conductivity across the interface between ¦ adjacent discs is relatively low. A low effective thermal conductivity may be achieved with commonly available material .
il by using steel washers having roughened surfaces, for example, " a surface roughness of 200~ in. It has been found that , ordinary steel washers with no special roughening of their l surface provide an overall low effective thermal conductivity.
; l, The stacked discs are extremely effective in ' producing a low thermal conductivity. Heat transfer coefficients i!on the order of 0.5 BTU/~IR-FT- F are achievable compared to 20 ~180 BTU/HR-FT- F for a solid piston body-crown interface.
' It should be noted also that a greater or lesser number of ,'discs may be employed to achieve a greater or lesser thermal conductivity. Since the diameter of the discs 56 does not 'extend to the peripl-ery of the crown 20 or piston body 12, 25 ',-their thickness ib sclected so that the portion of the crown ~i20 outside of these discs 56 is out of contact with the 22 ' of piston body 12.
i , Furthermore, the discs 56 support crown 20 over a l' relatively broad annular planar area defined at its inner ¦, diameter by the diameter of hole 28 and at its outer diameter I by the diameter of discs 56. This area of contact minimizes 5 ¦i the unit pressure on the discs 56 for a given pressure in ¦~ combustion chamber 21 and therefore contributes to a low ;-¦¦ thermal conductivity across the interface between adjacent jl discs. The annular contact area divides the radius of crown-j 20 into approximately equal sections. It can be seen that 0~¦ the radial dimension of crown 20 between hole 26 and a point ¦i in line with the wall of hole 28 is approximately equal to the radial dimension between the periphery of discs 56 and the outer periphery of crown 20. The bendiny loads on the ll top of crown 20 due to combustion pressures are therefore lslJ equalized.
¦' The discs 56 shown in figure 1 constitute one way ll of insulating crown pis~on body 12. Figure 2 shows an 'i alternate form of interface 54' which uses a disc 64 which . .
Ij has a relatively low conduc-tivity. This disc 64 may be 20', formed of porous metal or of steel wool compressed sufficiently to resist compressive loads. In certain instances it may be also advantageous to use a plurality of discs 64.
With any of the interface materials described ,l above, the crown 20 is effectively insulated from the piston 25 i body 12, u5ually formed of high conductivity aluminum. This , insulation provides a primary advantage of minimizing the thermal gradient between the upper and lower surfaces 24 and 58 of crown 20. As such internal thermal stresses are ', substantially minimized. This permits the material selection ii ' - 6 -I
: - I -, , . .
1l .
jjfor crown 20 to be very flexible since the material only must be able to withstand combustion temperatures and resist moderate compressive loads. The temperature gradient for ¦ithe most part is taken up by the interface 54 between the ' 5l,~crown 20'and piston body 12. Since the only load on it is~a ilcompressive one, the thermal stress caused by the temperatur.e j~gradient is not as detrimental as it would be if it occurred , !l , . .
'in the,crown 20. With the plurality of discs,~the gradient is distributed over a plurality of interfaces thereby mini'mizing 101 the stresses on the individual elements.
~' i ~ Any varia~tions in thermal expansion which occur between the piston body, interface 54 and crown 20 are compensated for by the spring assembly 50 to assure a relatively l!uniform compressive loading holding the parts together.
15 1l Since the shoulder 42 is larger in area than that available on the body 12,-for receiving the spring assembly S0, spacer ' I element 46,assures a greatly improved seat for carrying the : j;joint load on the body ].2. , 1', The above piston achieves the objec'tives of a well 20i~insulated combustion chamber to increase efficiency and to reduce emissions. 'Furthermore it does so with an economlcal, , , .
, ,.effective construction that permits ready replacement of the : ' parts.
!
. .
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A piston for an internal combustion engine, said piston comprising:
a generally annular crown portion of temperature resistant material said crown portion having a circular periphery;
a generally annular piston body having a circular periphery, said crown portion and said piston body having opposed planar surfaces;
a plurality of stacked discs having a relatively low conductivity planar interface between adjacent discs and positioned between the opposed planar surfaces of said crown and piston body for forming a low effective thermal conductivity interface, the planar surface of said crown extending radially outward at least as far as the periphery of said discs; and, means for fastening said crown portion to said piston body, whereby the temperature gradient across said crown is minimized.
a generally annular crown portion of temperature resistant material said crown portion having a circular periphery;
a generally annular piston body having a circular periphery, said crown portion and said piston body having opposed planar surfaces;
a plurality of stacked discs having a relatively low conductivity planar interface between adjacent discs and positioned between the opposed planar surfaces of said crown and piston body for forming a low effective thermal conductivity interface, the planar surface of said crown extending radially outward at least as far as the periphery of said discs; and, means for fastening said crown portion to said piston body, whereby the temperature gradient across said crown is minimized.
2. A piston as in claim 1 wherein said fastening means includes means for eliminating the detrimental effect of variations in thermal expansion of the elements making up the crown piston body combination.
3. A piston as in claim 2 wherein said crown and said piston body have aligned holes, the one in said piston body terminating in an interior recess thereof, and wherein said fastening means comprises:
a bolt extending through said holes and having a head positioned on said crown and a threaded portion extending through said piston body to said interior recess, a nut threaded onto said bolt; and, means positioned between said nut and said piston body for yieldably urging said piston body and crown towards one another.
a bolt extending through said holes and having a head positioned on said crown and a threaded portion extending through said piston body to said interior recess, a nut threaded onto said bolt; and, means positioned between said nut and said piston body for yieldably urging said piston body and crown towards one another.
4. A piston as in claim 3 wherein said bolt is formed from a high temperature, high strength alloy.
5. A piston as in claim 3 wherein said yieldable urging means comprises spring means positioned around said bolt and acting against said nut and said piston body.
6. A piston as in claim 5 wherein said spring means comprises a plurality of belleville washers.
7. A piston as in claim 6 wherein said piston body is formed of aluminum and wherein:
said piston body has a larger diameter hole than the one through said crown; and said piston further comprises a steel sleeve-like insert received in said opening of said piston body, said insert having a flange which abuts the interior recess of said piston body, said washers acting between said insert and said nut.
said piston body has a larger diameter hole than the one through said crown; and said piston further comprises a steel sleeve-like insert received in said opening of said piston body, said insert having a flange which abuts the interior recess of said piston body, said washers acting between said insert and said nut.
8. A piston as in claim 3 wherein said discs each have a central hole through which said bolt extends to thereby align said discs.
9. A piston as in claim 1 wherein said discs do not extend to the periphery of the interface between the crown and said piston body, the overall thickness of said stacked discs being selected so that the crown and said piston body are maintained out of contact with one another.
10. A piston as in claim 9 wherein said piston body has a central annular recess so that compressive loads on the crown are transmitted to the piston body across an annular area, the radios of said annular recess being approximate equal to the difference in radius between the crown and the outer periphery of the discs whereby a uniform bending load is imposed upon the crown by compressive forces.
11. A piston as in claim 1 wherein said discs are formed from steel having roughened faces.
12. A piston as in claim 1 wherein said crown and said piston body have aligned holes and wherein:
said fastening means extends through said holes to maintain said crown, disc means and piston body in compression;
and, said disc means have a central opening through which said fastening means extends.
said fastening means extends through said holes to maintain said crown, disc means and piston body in compression;
and, said disc means have a central opening through which said fastening means extends.
13. A piston as in claim 1 wherein said crown is formed from ceramic material.
14. A piston as in claim 1 wherein said crown is formed from heat resistant metallic material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US75576076A | 1976-12-30 | 1976-12-30 | |
| US05/861,467 US4242948A (en) | 1977-12-16 | 1977-12-16 | Insulated composite piston |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1078274A true CA1078274A (en) | 1980-05-27 |
Family
ID=27116125
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA294,075A Expired CA1078274A (en) | 1976-12-30 | 1977-12-29 | Insulated composite piston |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5395415A (en) |
| AU (1) | AU507729B2 (en) |
| BR (1) | BR7708699A (en) |
| CA (1) | CA1078274A (en) |
| FR (1) | FR2376348A1 (en) |
| MX (1) | MX144594A (en) |
| SE (1) | SE432463B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113202654A (en) * | 2021-05-18 | 2021-08-03 | 大昌汽车部件(苏州)有限公司 | Combined engine piston and forging process thereof |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55140764A (en) * | 1979-04-16 | 1980-11-04 | Tokyo Shibaura Electric Co | Diesel engine part |
| JPS5874853A (en) * | 1982-10-13 | 1983-05-06 | Toshiba Corp | Piston head |
| JPS60190650A (en) * | 1984-03-13 | 1985-09-28 | Ngk Insulators Ltd | Engine piston and manufacturing method thereof |
| JP2526947B2 (en) * | 1987-12-14 | 1996-08-21 | いすゞ自動車株式会社 | Insulation engine structure |
| DE102005041409A1 (en) * | 2005-09-01 | 2007-03-08 | Mahle International Gmbh | Two-piece piston for an internal combustion engine |
| WO2007068222A1 (en) * | 2005-12-17 | 2007-06-21 | Mahle International Gmbh | Two-piece piston for an internal combustion engine |
| KR101709624B1 (en) * | 2009-08-06 | 2017-02-23 | 페더럴-모걸 코오포레이숀 | Low thermal conductivity piston and method of construction thereof |
-
1977
- 1977-12-26 FR FR7739214A patent/FR2376348A1/en active Granted
- 1977-12-27 JP JP15673277A patent/JPS5395415A/en active Granted
- 1977-12-28 BR BR7708699A patent/BR7708699A/en unknown
- 1977-12-29 SE SE7714878A patent/SE432463B/en unknown
- 1977-12-29 CA CA294,075A patent/CA1078274A/en not_active Expired
- 1977-12-30 AU AU32102/77A patent/AU507729B2/en not_active Expired
-
1978
- 1978-01-02 MX MX171849A patent/MX144594A/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113202654A (en) * | 2021-05-18 | 2021-08-03 | 大昌汽车部件(苏州)有限公司 | Combined engine piston and forging process thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2376348A1 (en) | 1978-07-28 |
| SE7714878L (en) | 1978-07-01 |
| JPS5637419B2 (en) | 1981-08-31 |
| BR7708699A (en) | 1978-08-22 |
| FR2376348B1 (en) | 1981-01-23 |
| JPS5395415A (en) | 1978-08-21 |
| AU507729B2 (en) | 1980-02-28 |
| MX144594A (en) | 1981-10-28 |
| AU3210277A (en) | 1979-07-05 |
| SE432463B (en) | 1984-04-02 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |