JPH0666200A - Hybrid piston for high-temperature engine - Google Patents

Abstract

PURPOSE: To provide a hybrid piston for a high temperature engine which can operate under high temperature. CONSTITUTION: A piston has an upper part and a lower part connected by a bolt 18 of a heat resistant alloy, a nut 20 and a Belleville spring washer 19. The upper part i.e., the piston crown 16 has a cylinder engaging surface of a solid lubricant material, and the lower part i.e., the piston skirt 17 has a cylinder engaging surface including a liquid lubricant control means.

Description

Detailed Description of the Invention

[0001]

This invention relates to pistons for engines that operate at temperatures that are too high for conventional liquid lubricants.

[0002]

It is desirable to increase the operating temperature of internal combustion engines. This is because, in general, the higher the operating temperature, the higher the fuel consumption efficiency, the less emission, and the possibility of non-cooling operation without water. High engine temperatures are generally obtained by insulating the surfaces of the engine combustion chambers. However, if the engine operating temperature rises to about 355 ° F (177 ° C), conventional organic liquid lubricants begin to burn and break down, forming sludge deposits on the cylinder walls and in the ring grooves. To do. These deposits increase wear on the cylinders, pistons and piston rings, causing liner rubbing and ring sticking. 316 ° C for polyester-based liquid lubricants
It can withstand temperatures up to (600 ° F), but it is desirable to obtain higher operating temperatures. One way to obtain high engine operating temperature while minimizing liquid lubricant breakdown is to take advantage of the fact that the piston top temperature is always higher than the piston bottom temperature, as shown in FIG. The reason is that the top of the piston is directly heated by the combustion chamber in the cylinder, while the bottom of the piston is somewhat "insulated" by the middle part of the piston.
This is because the oil is cooled by the oil splashing on the bottom of the piston. As shown in FIG. 3, the temperature drops rapidly along the axial length of the cylinder liner from the top ring reversal point (TRR point). Therefore, one solution is to remove the piston ring, which is usually located around the top of the piston. This undulating piston is shown in FIG. In order for this solution to work, an oil control ring must be provided around the lower part of the piston (lower ring pack) to prevent oil from reaching the upper part of the piston. This technique prevents liquid lubricant from reaching around the top of the hot piston. Since there is no liquid lubricant around the top of the piston, it is possible to operate the engine at high temperatures. In theory, top ring inversion (TR
The temperature of the piston ring at point R (in the lowered piston pack) is low enough to prevent breakdown of the liquid lubricant. However, simply removing the upper piston ring presents other problems. That is, a problem arises in that a larger annular air gap is formed between the piston and the cylinder around the upper circumference of the piston. This dead air space results in poor air utilization, resulting in poor emissions and lack of brake specific fuel consumption. Another way to achieve higher operating temperatures is to completely remove the liquid lubricant and replace it with a solid lubricant. Solid lubricants can withstand higher temperatures and can be placed on the surface of the piston ring and on the surface of the cylinder wall. Examples of such solid lubricants include densified chromium oxide, Stellite 1 and Stellite 6 (obtained from Goshen's Stoudi Deloro Stellite Inc.), Hastelloy X Class (West Virginia, West Virginia,
Huntington's Incoalloys International), Triboli (from Metco Incorporated, Longeye, NY), copper alloyed with molybdenum, lead oxide or titanium, and lithium fluoride alloyed with copper or molybdenum. Can be mentioned. U.S. Pat. No. 3,675,738 discloses a piston having a solid lubricant disc made of calcium fluoride which engages the cylinder wall. U.S. Pat. No. 3,890,950 discloses a piston having a cylinder-engaging surface made of graphite. One advantage of dry lubricants is the elimination of particulate emissions resulting from oil consumption. The disadvantage of such solid lubricants is that they have a high coefficient of friction (0.20 to 0.50).
This is much higher than the coefficient of friction of liquid lubricants (about 0.04). Another drawback is the high wear rate of fixed lubricants alone. Therefore, it is desirable to have a piston system that simultaneously satisfies the low friction and long life of a liquid lubricant and the high temperature resistance of a solid lubricant. In liquid lubricated engines, it is also known to introduce a solid lubricant into the combustion chamber to further reduce friction. U.S. Pat.No. 3,994,697
U.S. Pat. No. 4,968,961 discloses a pellet consisting of a metal and a metal salt such as molybdenum disulfide, which pellet melts when placed in a gas tank to introduce a solid lubricant of the metal salt into the combustion chamber through the fuel system. . This is believed to reduce friction with a solid lubricant that fills the surface irregularities of the metal component and smoothes it. In addition, liquid lubricants and solid lubricants have been combined to form U.S. Pat. Nos. 4,127,491 and 4,284,518.
No. 4,349,444, and it is also known to make a single composition. Although the use of liquid and solid lubricants at the same time may reduce friction in some cases, these lubricants do not allow the engine operating temperature to be raised above the above limits. Recently NA
SA HESliney has developed a solid lubricant material (PS212) that has been tested in a Stirling engine.
This "PS212" material rubs against Stellite 6B Cr
Ag, CaF ₂ , and BaF ₂ are included in the C ₂ matrix.
(Journal of Vacuum Science and Technology, Vol 4
, No. 6l, Nov / Dec, 1986).

[0003]

SUMMARY OF THE INVENTION One object of the present invention is that the temperature at the piston top ring reversal (TRR) point is less than the breakdown temperature of polyester based liquid lubricants (about 316 ° C (600 ° F)). To provide a piston that is expensive. Another object of the present invention is to provide a piston with a cylinder engaging surface that has a coefficient of friction less than that of a solid lubricant and comparable to that of a liquid lubricant. Another object of the invention is to provide a piston that minimizes the annular dead air space around the piston above the top piston ring. Another object of the present invention is to
An object is to provide an engine that can utilize both solid and liquid lubricants. Another object of the present invention is to provide a region of dry lubricant in the top piston liner section to minimize particulate emissions from oil combustion. Other objects and advantages of the invention will be apparent to those skilled in the art from the following description of the preferred embodiments.

[0004]

SUMMARY OF THE INVENTION The present invention includes a piston having an upper portion and a lower portion. The upper portion comprises a cylinder engaging surface (such as a piston ring) made of solid lubricating material. The lower portion is provided with a cylinder engaging surface which comprises liquid lubricant control means. The distance between the upper and lower cylinder engaging surfaces is large enough to provide a temperature difference of at least 200 ° F (93 ° C) during normal engine operation. This is the bottom ring reversal (BRR) when the temperature of the cylinder liner at the top ring reversal point is above the breakdown temperature of the liquid lubricant.
It is suitable to maintain the temperature of the cylinder at the point below the breakdown temperature of the liquid lubricant. The desired temperature difference can be designed by the degree of insulation (insulation) between the top dry area and the lower wet area of the piston.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a cylinder 11 (including a cylinder liner 12), a reciprocating piston 13 and a cylinder head.
A combustion chamber of an engine is disclosed that includes 14 and a valve face 15. A suitable engine for this embodiment is 130.22.
A well-known 1Y73 caterpillar with a bore of mm (5.125 inches), a stroke of 165.1 mm (6.5 inches), a displacement of 2.2 liters (134.1 cubic inches), and a compression ratio of 16.5 to 1. All or part of the combustion chamber is described in U.S. Pat.
Insulation may be provided using a refractory oxide coating as disclosed in 542. The piston 13 is preferably an articulated piston as shown in FIG. 5 and comprises a piston crown 16 made of silicon nitride, titanium or other low thermal conductivity material and a cast iron piston skirt 17. However, these are connected by a bolt 18, a nut 20 and a disc spring washer 19 made of a heat resistant alloy. Ceramic fiber gaskets 21 and 22 are used for piston crown 16
Is sealed (insulated) from the piston skirt 17. The piston shown in FIG. 1 is at the top of its stroke and the top ring reversal (TRR) point in cylinder 11 is designated as 25.

The upper portion of the piston 13, namely the piston crown 16, is provided with a pair of compression rings 23, 24. These piston rings are made of M2 steel and have a cylinder liner.
It has a solid lubricant outer coating that engages 12. The solid lubricant can be any of the solid lubricants described above and can be applied using well known techniques. The lower part of the piston 13
Oil control means that engage the surface of the cylinder liner 12 (i.e.,
Equipped with oil control piston rings 26, 27). Liquid lubrication means, such as a conventional oil pump (not shown), communicates with the lower portion of piston 13 via the lower region 29 of the cylinder. The bottom ring reversal (BRR) point of the lower ring 26 is 28.
As instructed.

An important feature of the present invention is that the upper rings 23, 24 are
Is separated from the lower rings 26, 27 by an intermediate portion 31 of the piston 13, which intermediate portion when used in an internal combustion engine.
31 is to provide sufficient means to provide a temperature difference of about 93 ° C (200 ° F). Due to this temperature difference, the top ring
When the temperature of the cylinder liner 12 at the TRR point of 23 is above the breakdown temperature of the liquid lubricant, BR
The temperature of the cylinder liner 12 at the R point 28 can be maintained below the breakdown temperature of the liquid lubricant.

Another piston design is the articulated piston shown in FIG. A hot piston crown 71 is attached to the wrist pin 72, with this same wrist pin 72 attaching a cold piston skirt 73. The articulated piston design has no side thrust and therefore the upper piston ring 76,
Minimize the load on 77. This side thrust is supported by the lower piston skirt 73. Some stainless steel,
A low thermal conductivity wrist pin such as titanium or ceramic is used to completely insulate (insulate) the lower skirt from the hot piston crown and the upper piston ring
Significant temperature differences can be created between 76, 77 and lower piston rings 78, 79. An oil deflector can be used to prevent oil from splashing on the cylinder liner between the piston crown 71 gap and the piston skirt 73.

FIG. 2 is a composite view showing the piston of the present invention in the dead center position of the top 41 and bottom 40 within the cylinder. The distance between these positions is the stroke of the piston in the cylinder. The top ring movement area in the cylinder is shown as 42 and the bottom ring movement area is shown as 43. Since only the bottom rings 26, 27 are lubricated with a liquid lubricant, the part of the cylinder indicated by 43 has an oil film, while the part indicated by 44 remains substantially dry. The substantially dry region 44 has a lower portion 46 in which a small amount of oil is scraped from the lower region 43. This lubricant film is baked in the hot, dry region 44 to form a low friction film (compared to liquid lubricants) during high temperature engine operation.

Since the dry area 44 of the cylinder remains dry, it can withstand temperatures above the brake down point of the liquid lubricant. Since the upper rings 23, 24 use only solid lubricants, they can withstand these temperatures and therefore can be placed near the top of the piston to minimize dead air space and operate dry. Therefore, the utilization of air, the exhaust characteristics and the specific fuel consumption of the brake can be improved. The use of liquid lubricant for the bottom rings 26, 27 can reduce the coefficient of friction for the engine compared to using only solid lubricant for both the top and bottom rings.

The idea underlying the present invention can be understood with reference to FIG. FIG. 3 is a graph showing the expected peak temperature of the insulated cylinder liner in the region shown as 44 in FIG. 2 at various distances from the top of the combustion chamber. The combustion chamber temperature measured at the cylinder surface is not constant. This temperature is hotter at the top of the cylinder where combustion occurs. This temperature drops rapidly as the distance from the top of the cylinder increases.

Line 51 is 1300 ° F (704) at the TRR point.
Temperature for an engine insulated to achieve a peak temperature of (° C.), Line 52 is 1100 ° at the TRR point.
The temperature is given for an engine that is insulated to achieve a peak temperature of F (593 ° C). Modified according to the invention
For the 1Y73 Cataplar engine, the TRR point is 0.788 inches (20mm) from the top of the cylinder and the BRR point is 5.906 inches from the top of the cylinder (not shown in Figure 3).
It is located at (150 mm). As can be seen from Fig. 3, the breakdown temperature of the polyester-based liquid lubricant is 600 °.
F (316 ° C) is approximately 3.5 inches (89 mm) from the top of the cylinder
It is in place. However, this location is about 2.4 inches (61 mm) above the BRR point (top of region 43 in FIG. 2), where an oil slick develops, so that the oil is at a temperature high enough to cause lubricant breakdown. Not exposed to

As is apparent from the right hand portion of FIG. 3, the temperature of the cylinder block 11 and the cylinder liner 12 decreases with increasing distance from the top of the cylinder and with increasing distance from the cylinder surface.

Many modifications may be made to the above configuration to make various embodiments of the invention without departing from the spirit or scope of the invention. For example, the present invention can be used in either an articulated piston or a compound piston and is described in U.S. Pat.
It can be replaced by a disk of solid lubricant as disclosed in No. 8. Further, the surface of the cylinder can be coated with a dry lubricant. Therefore, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative of the invention and not in limitation.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a piston of the present invention.

FIG. 2 is a partial cross-sectional view showing the piston of the present invention in a top dead center position and a bottom dead center position within the cylinder.

FIG. 3 is a graph showing calculated peak temperature of an insulated cylinder liner at various depths and distances from the top of the combustion chamber.

FIG. 4 is a cross-sectional view of a prior art piston showing what the temperature distribution in a piston crown would be if used in a high temperature engine.

FIG. 5 is a cross-sectional view of another embodiment of an articulated two-piece piston according to the present invention designed to minimize side thrust.

[Explanation of symbols]

 13 Piston 16 Upper part (piston crown) 17 Lower part (piston skirt) 12 Cylinder liner 25 Top ring reversal point 28 Bottom ring reversal point

Claims (10)

[Claims] 1. A cylinder engagement surface comprising a piston body having an upper portion and a lower portion, the upper portion comprising a cylinder engaging surface of solid lubricant material, the lower piston portion including liquid oil lubricant control means. A piston characterized by having a surface. 2. The cylinder engaging surface of the upper piston portion and the cylinder engaging surface of the lower piston portion are a distance sufficient to provide a temperature difference of at least 200 ° F. (93 ° C.) when used in an internal combustion engine. The piston of claim 1, wherein the pistons are spaced apart. 3. The cylinder engaging surface of the upper piston portion and the cylinder engaging surface of the lower piston portion have a bottom when the temperature of the cylinder at the top ring reversal point is equal to or higher than the breakdown temperature of the liquid lubricant. A piston according to claim 1, wherein the pistons are separated by a distance sufficient to maintain the temperature of the cylinders at the ring reversal point below the breakdown temperature of the liquid lubricant. 4. An engine having a combustion chamber having a cylinder and a reciprocating piston that strokes in the cylinder, the piston having an upper portion and a lower portion, the upper piston portion being solid. A cylinder engaging surface made of a lubricant material, the lower piston portion having a cylinder engaging surface with liquid lubricant control means, the engine comprising a liquid lubrication device in communication with the lower portion of the piston. An engine characterized by being equipped. 5. The cylinder engaging surface of the upper piston portion and the cylinder engaging surface of the lower piston portion are at least 93 ° C. (200 ° F.) when used in an internal combustion engine.
5. The engine of claim 4, separated by a distance sufficient to provide a temperature difference of 6. The cylinder engaging surface of the upper piston portion and the cylinder engaging surface of the lower piston portion have a bottom when the temperature of the cylinder at the top ring reversal point is equal to or higher than the breakdown temperature of the liquid lubricant. The engine of claim 4, wherein the cylinders are separated by a distance sufficient to maintain the temperature of the cylinders at the ring reversal point below the breakdown temperature of the liquid lubricant. 7. The engine according to claim 4, wherein at least a part of the combustion chamber is thermally insulated. 8. A method of operating an internal combustion engine comprising a cylinder having a reciprocating piston therein having an upper portion and a lower portion; providing a cylinder engaging surface of solid lubricant in the upper piston portion. Providing the lower piston portion with a cylinder engagement surface comprising liquid lubricant control means. 9. The cylinder engaging surface of the upper piston portion and the cylinder engaging surface of the lower piston portion are at least 93 ° C. (200 ° F.) when used in an internal combustion engine.
9. A method of operating an internal combustion engine according to claim 8, characterized in that they are separated by an insulating means sufficient to provide a temperature difference of 10. The cylinder engaging surface of the upper portion and the cylinder engaging surface of the lower piston portion have a bottom ring when the temperature of the cylinder at the top ring reversal point is equal to or higher than the breakdown temperature of the liquid lubricant. 9. The operating method of claim 8 wherein the cylinder liners at the inversion point are separated by a distance sufficient to maintain the temperature below the breakdown temperature of the liquid lubricant.