Abstract:
The piston sleeve has a radial positioning surface adjacent to the top surface and an axial positioning surface separated from radially positioning surface by a coolant contact surface. A piston bore extending the length of the piston sleeve is machined to form a non-cylindrical bore. The sleeve is compressed by applying force to the top surface and to the axial positioning surface. The piston sleeve is also heated to a normal working temperature. The compression force and the force due to thermal expansion deforms the piston sleeve and changes the non-cylindrical bore into a substantially cylindrical bore.

Description:
This invention relates to a piston sleeve with a mid stop, for a high compression engine, and a contoured bore that becomes a cylindrical bore under operating conditions. 
     BACKGROUND OF THE INVENTION 
     Piston sleeves employed in high compression engines have generally had a flange on their top or head end that is clamped in place between the block and the cylinder head. The skirt of these piston sleeves is permitted to float due to thermal expansion and contraction. The elongation and contraction of piston sleeves that are dry has not been a problem. However cooling capacity must be somewhat larger with dry sleeves than with wet sleeves to insure adequate cooling. 
     High compression engines designed in recent years have generally had wet piston sleeves to improve cooling, reduce the coolant capacity requirement for their cooling systems and thereby reduce vehicle weight. 
     Piston sleeves with a top flange, as described above, that are in direct contact with engine coolant require sealing devices to seal between the sleeve skirt and the block. Such seals have durability problems. These durability problems are caused by movement between sleeve skirts and engine blocks due to thermal changes, engine vibrations, corrosion on the wet side of the sleeves, cavitation, seal material degeneration and other causes. Any leakage of coolant with antifreeze into an engine crankcase is a potential disaster. The water will be turned to vapor by crankcase heat and expelled from the crankcase. The antifreeze will not evaporate and therefore remains in the engine. Antifreeze is incompatible with engine lubrication systems and will cause moving parts to seize. Piston sleeve seal devices generally have a moderate failure rate during their first six thousand hours of operation or so. The seal device failure rate generally becomes unacceptable above ten thousand hours or so. 
     Engine designers are now designing engines with wet piston sleeves, each of which is anchored on the block by a radially extending flange that is mid way between the top end and the crankshaft or bottom end. The radially extending flange has an axial positioning surface in direct contact with a stop surface on the engine block. The sleeve is axially loaded between the cylinder head and the engine block stop surface to eliminate leakage of gasses and coolant. As a result, a seal device is not required between the block stop surface and the radially extending flange mid way between the sleeve ends. However, an appropriate seal device can also be employed if desired. 
     The axial load required to seal between a piston sleeve and the cylinder head and a block stop surface is substantial. The seal between the top end of the sleeve and the cylinder head must prevent the passage of compressed air prior to combustion and the pressure of hot gasses following combustion. In high output diesel engines that are turbocharged, the pressure in the combustion chamber is substantial. The seal between the axial positioning surface and the block stop surface generally does not require a large axial load. However, both seals must maintain a seal when the engine is cold as well as when the engine is hot. 
     The axial load on a piston sleeve with a mid stop that is required to prevent leakage between the top of a sleeve and a cylinder head and to prevent leakage between an axial positioning surface on the radial flange and a block stop surface under all possible operating conditions is large. An axial load on the piston sleeve that prevents leakage of gas and coolant, under a full range of operating conditions, distorts the inside walls of the piston sleeve. This distortion of the walls increases the rate of sleeve wall, piston and piston ring wear. The distortion also increases oil consumption, blow by, emissions of undesirable materials, and will eventually result in power loss. To minimize piston ring wear and all of the associated problems, the inside walls of the piston sleeves should be cylindrical or close to cylindrical under normal operating conditions. 
     One solution to the piston sleeve distortion problem has been proposed. This proposed solution is to provide thicker sleeve walls from the top edge to the mid stop. Thicker sleeve walls increases the weight of each sleeve and thereby increases the engine weight. A sleeve with an increased outside diameter requires a larger bore in the engine block. An increase in the diameter of the bores in the engine block will generally make it necessary to increase both the length and the width of the block to accommodate the larger bores for the piston sleeves and maintain coolant capacity. Increasing the block size obviously increases block weight and will generally make it necessary to increase the size and weight of other engine components. 
     SUMMARY OF THE INVENTION 
     The piston sleeve for a high compression internal combustion engine is a tubular member. The tubular member has a top surface, that is perpendicular to an axis of the tubular member, and a bottom surface. A radial positioning surface is adjacent to the top surface. An axial positioning surface faces axially toward the bottom surface and is between the top surface and the bottom surface. A radially outward facing coolant contact surface is between the radial positioning surface and the axial positioning surface. A skirt extends from the axial positioning surface to the bottom surface. A profiled radially inward facing surface extends substantially from the top surface to the bottom surface. The profile becomes substantially cylindrical when the piston sleeve is in a high compression internal combustion engine block and a predetermined axial compression force is applied to the top surface and to the axial positioning surface. 
     The piston sleeve provides a joint between its top surface and a cylinder head that holds products of combustion in the combustion chamber. Contact between the axial positioning surface of the piston sleeve and the engine block retains engine coolant and keeps coolant out of the crankcase without the use of a seal device. The cylindrical cylinder wall surface that is formed inside the sleeve during normal operation reduces piston ring wear, piston wear and sleeve wear. The cylindrical surface also reduces oil consumption blow by and undesirable emissions from the engine. 
     Piston sleeves for diesel engines with profiled cylinder walls as described above can be pressed into an internal combustion engine and ready to use as received from the factory. Expensive and time consuming honeing, polishing and cutting operations in the field are eliminated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein: 
     FIG. 1 is a sectional view of a piston sleeve mounted in an internal combustion engine; 
     FIG. 2 is a sectional view of a prior art sleeve with a top flange that axially positions the sleeve in an internal combustion engine and with parts broken away; 
     FIG. 3 is a sectional view of a prior art sleeve with a mid stop showing the inside wall profile when loaded and with parts broken away; 
     FIG. 4 is a sectional view with the piston sleeve mounted in an engine block but not axially loaded and with parts broken away; 
     FIG. 5 is a sectional view with the piston sleeve mounted in an engine block, axially loaded and with parts broken away; 
     FIG. 6 is a vertical sectional view of the piston sleeve prior to axial loading; and 
     FIG. 7 is a view similar to FIG. 6 showing the sleeve axially loaded. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A piston sleeve  10  for an internal combustion engine  12  is a tubular member with an axis  14 . The sleeve  10  has a top surface  16 , a bottom surface  18 , a radially inner surface  20  and an outer surface  22 . The top surface  16  is in a plane that is perpendicular to the axis  14 . The bottom surface  18  is also in a plane that is perpendicular to the axis  14 . The top surface  16  is separated from a surface  24  on the cylinder head  26  by a gasket  25 . Normally the block top surface  28  of the engine block  30  is perpendicular to the axis  14  of the piston sleeve  10 . It is convenient to have the sleeve top surface  16  in a plane that is parallel to the top surface  28  of the engine block  30 . By placing the top surface  16  of the piston sleeve  10  in a plane that is perpendicular to the axis  14 , force exerted on the sleeve by the cylinder head  26  is exerted in a direction that is parallel to the axis  14 . There is no uneven force on the sleeve  10  that is transverse to the axis  14  and would tend to bend the sleeve. The bottom surface  18  is not in direct contact with any other object or surface. The bottom surface  18  of the sleeve  10  can be any shape within limits. 
     The outer surface  22  of the piston sleeve  10  has a radially positioning surface  32  adjacent to the top surface  16 . This positioning surface  32  has a diameter that exceeds the diameter of the bore  34  in the internal combustion engine block  30 . A press forces the radial positioning surface  32  into the bore  34  forming an interference fit that prevents leakage of coolant from the coolant jacket  36 . 
     An axial positioning surface  38  on the piston sleeve  10  is between the top surface  16  and the bottom surface  18  and adjacent to the lower portion of the coolant jacket  36 . As shown in the drawing, the axial positioning surface  38  is in a plane that is transverse to the axis  14 . An engine block stop surface  40  is contacted by the axial positioning surface  38  and limits axial movement of the piston sleeve  10  toward the crankshaft  42 . The engine block stop surface  40  is also in a plane that is transverse to the axis  14 . The bore  44  in the block  30  provides clearance for the piston sleeve  10  thereby relying upon the bore  34  in the block to radially position the sleeve. Axial pressure on the top surface  16  of the sleeve  10  forces the axially positioning surface  38  into engagement with the block stop surface  40  and forms a coolant tight seal. If desired, a mechanical type seal device such an O ring could be employed. A mechanical seal device is not required however. 
     The axial positioning surface  38  and the block stop surface  40  could be conical mating surfaces that would fix the bottom surface  18  radially if desired. The diameter of the bore  44  could also be reduced to radially fix the bottom surface  18  if desired. 
     A coolant contact surface  46  extends from the radial positioning surface  32  to the axial positioning surface  38 . Coolant in the coolant jacket  36  of an internal combustion engine  12  carries heat away from the coolant contact surface  46 . A water pump (not shown) pumps coolant through the coolant jacket  36  and through a heat exchanger such as a radiator. The coolant contact surface  46  preferably has a diameter that is smaller than the diameter of the radial positioning surface  32  so that corrosion on the coolant contact surface does not prevent removal of a worn or damaged piston sleeve  10 . 
     A skirt  48  extends axially from the axial positioning surface  38  to the bottom surface  18 . The radially outer surface of the skirt  48  may be in contact with gasses and lubricant in the crankcase of the internal combustion engine  12 . The outer diameter of the skirt  48  is smaller than other outer surfaces of the piston sleeve  10 . 
     The reduced diameter of the skirt  48  reduces weight of the piston sleeve  10  and exposes the axial positioning surface  38 . Loading on the skirt  48  is substantially less than loading on the sleeve  10  above the axial positioning surface  38 . This reduced strength requirement permits the outside diameter of the skirt  48  to be reduced. 
     Clamping the cylinder head  26  to the engine block  30  places a substantial axial load on the piston sleeve  10 . The load on the top surface  16  of the sleeve  10  is primarily a compressive load. Minor distortion of the inside or radially inner surface  20  of the piston sleeve  10  occurs near the top surface  16  and the axial positioning surface  38 . This distortion causes the inside surface  20  to move radially inward near the top surface  16 . The load exerted on the axial positioning surface  38  by the engine block stop surface  40  places bending loads on the piston sleeve  10  that warps the inside surface  20 . 
     The prior art piston sleeve  50  shown in FIG. 3 has a substantially cylindrical surface  52  before a cylinder head  26  is clamped to the engine block  54 . A wavy line  56  indicates the warpage (exaggerated) when the prior art sleeve  50  is clamped in place in a block  54 . 
     The piston rings  60  on a piston  62  are radially compressed springs that tend to expand and follow the contour of the inside surface  20  of a sleeve  10 . If the inside surface is warped as shown by the wavy line  56  in FIG. 3, a piston ring  60  is continuously expanding or contracting. This movement reduces the life of each ring  60  and wears the ring groove  64  in the piston  62 . When the loaded piston sleeve  10  has a substantially cylindrical inside surface  20 , the piston rings  60  have little change in diameter and wear is minimized. 
     The unloaded piston sleeve  10  shown in FIG. 6 has been machined so that the inside surface  20  will be substantially cylindrical when axially loaded and running at the expected operating temperature. The unloaded profile is obtained by determining the quantities of material to be removed or added to change the warped profile  56  to a straight line. Removing and adding material changes the strength of the piston sleeve  10  where material is removed or added. The changes in strength requires modification of the final unloaded profile of the inner surface  20  of the piston sleeve  10 . 
     The operating temperature of a piston sleeve will vary along the length of the sleeve from the top surface  16  to the bottom surface  18 . The operating temperature will also vary depending upon ambient temperature, engine load and fuel characteristics. The profile of an inner surface  20  of the piston sleeve  10  is also modified to correspond to the expected operating temperature of the sleeve in an internal combustion engine  12 . The inner surface  20  of a piston sleeve  10  in an internal combustion engine  12  that is operating at the expected temperature and engine load is substantially cylindrical as shown in FIG.  2 . If there are changes in engine load, ambient temperature, or other operating conditions from the expected operating conditions, axial load on the piston sleeve  10  will change and the inner surface  20  will be slightly warped. However, large high compression engines  12  generally run in a relatively narrow temperature range. Expected changes in the inner surface  20  profile are generally small. 
     A piston sleeve  10  manufactured as set forth above can be mounted in an engine  12  and the engine can be assembled without additional machining, honeing or polishing of the piston sleeve. 
     The prior art piston sleeve  66 , shown in FIG. 2 has a cylindrical rim  68 . This cylindrical rim  68  axially fixes the sleeve  66  in the block  70 . As explained above, with this arrangement there are essentially no axial loads on the sleeve  66 . However, the sleeve  66  expands and contracts axially with temperature changes. To prevent leakage from the water jacket and accommodate axial movement of the sleeve  66  relative to the block  70 , a seal  72  is provided. The seal  72  can accommodate the movement between the sleeve  66  and the block  70 . However, seals  72  have a limited life. A diesel engine with a long life needs an improved sealing system as described above to eliminate the coolant leakage that may occur with seals  72  after a period of time. 
     Obviously, many modifications and variation of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.