GB1600759A - Method of finishing coacting surfaces - Google Patents

Description

(54) A METHOD OF FINISHING COACTING SURFACES (71) I, STEVE ALBERT RANDS, a citizen of the U.S.A., of 4353355 East Floral Drive, Los Angeles, California 90022, U.S.A., do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of preparing two pieces of material (for example a piston and a cylinder) to finish them to a required size.

Despite the fact that the piston ring was invented over 100 years ago, it is only within the last 10 years or so that serious investigations have been conducted on cylinder wall finishing and the mating surfaces of piston rings to the cylinder walls. Research projects have been and are being conducted, with conflicting opinions on this subject. Since piston ring manufacturers do not have any control over the honing processes, they attempt to design piston rings that will accommodate surface finishes produced by their major customers.

One major development in the mass production of engines 15 to 20 years ago was the development of the diamond hone. This enabled manufacturers to bore their engine blocks or their cylinder liners within .001 to .002 of an inch and then to use the diamond hone to remove the rest of the material to a controlled size. The diamond hone performs this task very well but it has one bad feature--the hone is too hard, it is too sharp and with the great pressure required against the cylinder wall, it leaves an extremely peaky finish of cut, torn, and folded metal.

Valuable graphite flakes are often either removed from the surface of the cylinder or are smeared over with metal.

Rigid honing procedures, such as by a diamond hone, can properly size a cylindrical bore and refine the finish of the cylindrical bore to the extent that it produces an acceptable finish under present day standards. The rigid hone, however, produces a crosshatched configuration having valleytype indentations produced in the surface of the honed material by the abrasive grains embedded into the rigid hone stones. The crosshatch grooves produced by the hone are inconsistent, with some too deep or too fine.

This crosshatch pattern is a natural pattern that is caused by the rotation of the rigid hone and the longitudinal displacement of the hone in the cylinder.

In addition to the finished surface produced by a rigid hone, other surfaces known in the art are glazed and plateaued surfaces.

The glazed surface is essentially smooth throughout its extent without any valleys or subsurface pockets. A plateaued finish is one in which the surface peaks have been eliminated so as to provide a satisfactory bearing surface. A consideration of these various types of surfaces, and honing tools and procedures for finishing coacting surfaces and in particular cylindrical surfaces is the subject of a booklet published by Brush Research Manufacturing Co., Inc. of Los Angeles California entitled "An Observation of Some Common Practices in Cylinder Boring, Honing and Wall Finishing". This booklet discusses the characteristics of a plateau finish and the advantages of a crosshatch pattern utilized in conjunction with the plateau finish. It has been established that the use of a crosshatch pattern on the inside surface or the bore of a cylinder is effective for spreading oil sideways in both directions so as to cover the entire wall surface. For this purpose the grooves of the crosshatch pattern must be evenly spaced.

The most effective crosshatch pattern is one wherein the pattern has an angular relationship with respect to the horizontal between 2-23 degrees to obtain a 45 degree crosshatch pattern, as discussed in the aforementioned booklet. A crosshatch pattern care fully defined thereon is conditioned to permit a film of a lubricating medium or liquid such as oil to be maintained or stored in the subsurface valleys at all times to thereby eliminate any metal-to-metal contact and the problems resulting from such direct contact.

It is important to utilize such a crosshatch pattern since it is not only useful under dynamic operating conditions such as when an engine is in operation but also when the engine is stopped and standing still. The advantage of the production of a smooth top surface or a plateaued surface for the interior of a cylinder is that it provides an effective bearing surface for the coating elements such as piston rings that ride over the plateaued surface.

The plateaued wall finish is recognized as being an acceptable finish. A number of the major manufacturers of engine liners concede that such a plateaued surface would be meritorious in their products but do not include such finishes since they are of the opinion that the development of a plateaued finish is difficult and very expensive.

Engine failure can be classified as any engine that suddenly starts to consume large quantities of oil and has a large amount of blow-by. It usually requires immediate attention or there is a possibility of piston seizure that might even tear the liner apart. Many people drive nearly new automobiles that will consume up to 1 quart of oil every 500 miles and they may take it in for a claim or warranty or may continue to drive it and condemn the manufacturer for a bad engine.

One of the leading factors of engine failure is scuffing, or what may be described in Europe as scalds, burn-traces or burn marks.

When a piston ring drags on a cylinder wall without an oil film the heat that is generated builds up to such a point that there is a welding process that develops between the rings and the cylinder wall producing a metal transfer which is called scuffing. There are many underlying causes for scuffing but it is considered herein only as relative to the unacceptable cylinder wall finishes.

As mentioned in the aforementioned booklet of Brush Research Manufacturing Co., Inc. of Los Angeles, there has been developed a tool that permits a plateaued, crosshatch pattern to be readily developed.

Such a tool is presently available from Brush Research Manufacturing Company and comprises a resilient base hone carrying abrasive elements laminated to the ends of nylon filaments. The abrasive elements are of a common form and are available in almost any grit size from very fine to very coarse.

The principal features of the Flex-Hone tool are that during use it is self-centering, self-aligning to the bore and is self-compen sating for wear. The result of this is that the same consistent pressure is produced against every portion of a cylinder wall throughout its entire length and because it is selfcompensating for wear, it is going to give exactly the same finish in each and every cylinder. The Flex-Hone tool is self-controlled so that the same finish is obtained regardless of the operator and the only variations are the speed of rotation, or the actuation within the cylinder during its operation of the type of honing oil. Different pressures against the cylinder wall may be obtained by varying the filament diameters or the actual diameter of the hone itself either creating more or less pressure against the wall through the modulus of the nylon or through the speed of rotation. This honing tool is disclosed more fully in U. S. patents 3,384,915 and 3,871,139. This honing tool is disclosed in patent 3,384,915 as a glaze buster.

The use of a honing tool having a resilient base permits the desirable flat or plateaued surface to be developed on a cylinder wall with very little pressure on the walls while removing very little metal but removing the peaks from the surface. In the use of such a tool, in addition to providing the desired plateaued finish, it also produces the desired crosshatch pattern for oil retention purposes.

This is accomplished without gouging out the metal resulting in torn or folded-over edges.

The Flex-Hone tool has heretofore been employed for finishing the cylinder walls of engines that have been operating over a long period of time. Engines that have been in use for some time have had the peaks on the cylinder walls and the coacting piston rings run for a sufficient time period so that the coacting surfaces have produced a compatible finish. This compatible finish is produced by the abrasive elimination of the peaked finishes on the cylinder walls and piston rings simply through use. This engine condition is considered by those skilled in the art as an engine that has been "broken-in" or "runin". It is considered that at this stage of engine operation excessive oil consumption and high operating temperatures should be reduced. Improved operation of a used engine can be expected when a cylinder bore has been refinished by means of the abovedescribed Flex-Hone tool.

According to this invention there is provided a method of preparing two pieces of material to finish them to a required size when they are to be used in sliding contact that is produced by relative movement of the materials while working under pressure, the method including the steps of:- providing the two pieces of material with a required configuration and with mating sur faces finished so as to permit relative sliding movement between them; and flexibly finish honing each of the mating surfaces to provide each with a plateaued finish having a crosshatch pattern comprising a plurality of substantially similarly directed uniform grooves in two sets extending in two different directions angularly related to each other and also angularly related to a reference plane substantially perpendicular to the direction of the said relative movement between the two pieces of material.

It has been found that the use of such a plateaued crosshatch surface on both coacting surfaces of materials used in sliding contact under pressure will produce advantages not heretofore thought possible by simply controlling the finishes of these coacting surfaces. In the production of such coacting surfaces in a new internal combustion engine, for example, the "running-in" of the piston-cylinder units can be either eliminated or substantially speeded up in time since the normal cut-torn and folded metal finish that results from present day rigid honing techniques is eliminated, resulting in higher efficiency. The use of such controlled surfaces results in a saving of oil, a lowering of blow-by into the atmosphere eliminating some piston and cylinder wear and to some extent eliminating the "green-engine" that requires a heavier-than-needed starter. It also appears that the method of the invention may equally well be used in hydraulics and pneumatics to prolong the life of piston seals and give better sealing characteristics. Cross hole ports in engines may also be deburred and radiused by the method. The overall results are longer life, better performance and greater safety in operation of the devices having the desired finished surfaces.

The method of the invention as applied to the manufacture of engines results in a lower temperature between the interface of the ring and the cylinder bore, lowered blow-by and a defect-free bore surface which will retain a lubricant. Lowering the ring-bore interface temperature is helped by reducing the amount of friction, or the metal that the ring has to remove in its bedding-in process. In addition, the plateaued finish helps to eliminate initial wear and to give a larger bearing surface which in itself will reduce temperature by reducing the load on the piston ring and those sections of the cylinder bore at the point of contact. Greater area contact between the piston ring and the plateaued finish of the cylinder bore will lower the blow-by. A valley-type finish will help retain the lubricant which is needed for rapid ring seating and resistance to or elimination of scuffing. A crosshatch finish will also help spread the oil sideways on the up and down strokes of the piston instead of forcing it up into the combustion chamber. It is also expected that scuffing between the sliding surfaces will be reduced by the plateaued finishes.

In considering the surface finish on a piston ring, the cylinder wall or the main bearings of an engine, all of these items can be characterized as pieces of metal in contact for coaction under pressure. In present day applications neither of these two surfaces are completely smooth so that there will be a certain amount of interlocking present between the two surfaces.

There are differences in bearing pressure when different percentages of plateau on one square inch or one square centimeter of two contacting surfaces. In theory, on two completely flat surfaces, if we place 500 pounds of pressure on the top surface we should have 500 pounds per square inch pressure on the lower surface. If, for example, an 80 percent plateaued area is used, then we will have a surface pressure of 625 pounds per square inch. With a 40 percent plateaued area, the 500 pounds pressure will now increase to 1,250 pounds per square inch. With a 10 percent plateaued area, such as we would find in ari extremely peaked surface, then the bearing area is 1/10 which increases the pressure of the contacting surfaces up to 5,000 pounds per square inch. This is based upon the knowledge that the pressure on the surface is the load divided by the projected bearing area. This additional load caused by a peaky finish has a great effect on what happens when these two metal surfaces start rubbing together.

In a practical application, a diesel engine in a small boat proceeding at 15 knots is going to have piston rings that exceed speeds of 30 miles per hour within their stroke. They are going to stop and start an average of 4000 times a minute and during an hour of running time are going to be dragged across the cylinder surface a distance of 19 miles. A metal realization of this will emphasize the importance of the surface finish that is needed on a cylinder wall when you think of the punishment that the piston ring is going to be subjected to in the first hour of running on a cylinder that may have a peaked finish.

A proper bearing surface for a cylinder bore or the like should provide a plateaued area of from 60 to 80 percent of the cylindrical surface.

To utilize a lubricant between sliding or coacting surfaces is well known but it is also important to bring about a condition that is going to permit a lubricating film to be retained between the two metals so that there is no metal-to-metal contact. The viscosity of the oil utilized between these surfaces has been found to be very important as well as other factors. Some of these factors are the blow-by that removes the oil from between the top ring and the piston wall, the pressure of the ring against the wall which squeezes the oil from the surface and heat that destroys it. There must be a film of oil between these two rubbing or coacting sur faces if we are going to prevent metal-tometal contact because the moment we do have this contact then we are going to have a condition which will lead to excessive heat and possible temporary welding of one surface to another.

There is solid friction and fluid friction and there are three major features to determine the amount of each. Solid friction is the load or the amount of pressure that is placed upon the metal whether it be a ring or a bearing. Three factors in order of importance are first, the contact area which supports the load; second, the speed at which it travels; and third, the viscosity of the oil itselfcon- tact area, speed and lubrication. Consider the fact that oil is going to be squeezed out either by the pressure of the ring against the cylinder wal or the pressure of the connecting rod against the bearing. In order to have full film lubrication, the oil must be replaced faster than it is squeezed out. If the speed is too great or the area is too small for the load, then solid friction with accelerated wear is going to be the result. When an engine is started up from a standing stop, we are going to pass through three phases of lubrication.

This period of time will last from the time you start the engine until you see the oil pressure gauge reach its proper operating pressure. We will probably start off by having almost metal-to-metal contact with very little or no lubrication. Then, we will have a thin film-a boundary or border-like lubrication. Then a thick film or a full film lubrication. It is very important, therefore, to have a surface that is capable of being wetted out or a surface that is going to maintain and hold a thin film of oil either when the engine is in operation or after it has stopped and is standing still. With a porous surface as you might find in some chrome cylinders or in some chrome rings, the oil will drain from the porosity whereas if you have a proper crosshatch finish with the proper valleys for oil retention, the oil may remain wetted out on the surface. Viscosities of oils are an extremely important consideration at this point depending upon compression ratios, clearances, types of rings and cylinder wall surfaces, engine types, lubrications, heat of the engines, etc.

A piston on its upstroke takes all of the air that has been sucked into the cylinder on its downstroke and compresses it to a ratio of either 8 to 1 or 22 to 1, or any range in between. This pressure gradually builds up not only on the top of the piston but also on the piston ring and the pressure gets down in behind the ring and forces it outward to the cylinder. On a diesel the compression of these gases builds up heat until it reaches an ignition point and we have a resulting heat flame that in the combustion area is probably as hot, if not hotter, than an oxyacetylene torch. This instant heat, of course, expands the top of the cylinder head and piston, and the top ring and also the top part of the liner.

At this point, we have some distortion prior to the downward movement of the piston. If the ring is not mated or seated to the cylinder the greatest blow-by is going to be at this initial point of contact or lack of contact.

Any blow-by is going to escape past the top ring, past the junction of the split in the ring (or at the horns) and the pressure is going to continue down to the second compression ring. The action there is going to be the same as with the first, where the pressure is going to get in behind the ring and force it to the surface. There is a second danger at this point that we might suffer ring collapse of the first ring and oil carbonization might build up between the ring and its groove which will prevent its future function and ring breakage will result. Sometimes there is so much blow-by on the first ring that the major part of the pressure is on the second ring as we quite often see scuffing starting to develop at the second ring before we see scuffing on the first one. If these hot blow-by gases escape between the ring and the cylinder wall, then at this point any oil film that might be there is going to be burned off.

When we talk about the use of the Flex Hone, we always say to be sure to bring the Flex-Hone out of the cylinder while it is still rotating, because we want to produce a uniform crosshatch finish completely throughout the entire length of the cylinder and particularly at the top of the ring travel.

This advice then becomes more apparent to you because of the utmost necessity of trying to have a plateaued finish at the top of the ring travel to eliminate as much as possible the initial blow-by without destroying whatever oil film might be there. The pressure of the ring to the cylinder wall is going to have a squeeze action on whatever lubrication might have been placed there by the upward travel of the piston before its power stroke and by the connecting rod splashing or otherwise depositing oil on the cylinder wall itself. On its downward stroke the oil rings are going to scrape the oil back into the oil reservoir in the pan. The cylinder wall is cooled by the oil as the oil becomes a heat sink. It is also going to be cooled in a wet sleeve by the water circulating around the portions of the liner. The block itself is also going to be cooled by the oil going down through the oil galleries. The piston and the ring which are much hotter than the cylinder wall, are going to be cooled by the cylinder wall itself on its downward stroke and by the taking in of new air. We see that we have expansion and contraction of the piston and the rings and actually the liner itself. One of the major causes of scuffing, particularly in the early running-in stages, is this initial lack of seating on a peaked finish which might be alleviated greatly by having a plateaued finish. All of this is extremely important on a new engine where a plateau might help eliminate or alleviate the start of the troubles.

A peaky finish will give us less contact area for the rings themselves, thus greatly increasing the load or the pressure. Because of the lessening of this contact area we have the possibility of greater blow-by thus destroying the oil film with greatly increased temperatures. This results in the rings themselves heating to a point whereby they might melt the peaked metal off the cylinder wall and weld it to the ring. At this point, we have scuffing.

The rings themselves often have to do the final honing job and remove by abrasion all the peaks from the surface of the cylinder wall. In doing this the metal is worn away, embedding particles of this metal into the cylinder itself and sometimes into the ring. If you have chrome rings, the chrome laminate is sometimes removed from the ring face itself. The heat reaches such a temperature that instead of the metal being worn down in a normal abraded fashion by the rings, it is smeared in a plastic formation against the cylinder wall. This is evident in some of the cylinder wall surfaces that are examined after a failure during a running-in process.

This plastic deformation or smearing of the metal down a cylinder wall removes all of the necessary crosshatch that is needed to hold a film of oil. The rigid hone often covers up in its smearing and plowing action the very important graphite particles that are part of the cylinder wall surface. These graphite particles besides being a lubricant themselves will also hold large amounts of lubrication while the Flex-Hone tool will cut the surface finish clean and expose the graphite particles.

This opening up of the surface permits oil retention and lubrication. Otherwise, this plastic deformation of the cylinder wall metal and the changing of the micro-substructure to an inferior status is compounded and additional scuffing is an inevitable result.

Rings of all types have been experimented with and tested in order to give the optimum contact area to the cylinder wall to prevent the rings from sticking, and allowing them to operate freely within the ring grooves and to have the proper outward pressure caused by the expanding gasses in the power stroke.

Many different shapes and surface finishes and surface treatments have been developed mainly in order to accommodate a particular engine manufacturer to overcome blow-by, excessive heat, elimination of oil film, smearing of the metal and the resulting scuffing.

Piston ring manufacturers normally have no control over cylinder wall finishes, but try and develop a ring to meet an engine manufacturer's specifications. Many different shapes-barrel faced, positive twist, reverse twist, head land, etc. designs-have been produced from grey iron to ductile iron from thicknesses of 1/8-inch down to 1/16inch, with some chrome faced, chrome sided, treated with molybdenum and other hard facing materials, and experiments with exotic materials. Some of these changes were undoubtedly made for economy and speed in the manufacture of the rings and the pistons to house them. Positive and reverse twists were intended to provide seals against blowby and oil, but few took into consideration the damaging abrasive punishment given to them in the ring seating process while the peaky finish normally found in a rigid honed cylinder is worn down to develop the plateaued finish that will produce "ring seating". Usually the rings also have this peaky finish, and in the case of the molybdenum (moly) ring, the ring is not only peaky but also hard, so that the attrition of the peaked finish on both cylinder and ring will equalize to end up with a plateau on both metal faces.

In accordance with the invention, the piston ring is modified to mate with a plateaued finish on a cylinder wall surface, such as that produced with a Flex-Hone tool.

The peaky finish on a ring is not only unnecessary but undesirable and the ring face is also plateaued and crosshatched.

Comparison tests have been conducted under different conditions of surface finishes of the piston and cylinder units of a standard commercially available engine. The tests were conducted on the basis of original equipment manufacturers, OEM, finishes, Sunnen honing tool finishes and a Flex Honed tool finish. The tests were conducted to determine the effect of the finishes on the engine with respect to oil consumption, blow-by, compression readings, ring gap increase and fuel dilution. The finish produced by the Flex-Hone tool that produced a plateau finish with the desired crosshatch pattern indicated a saving in oil, lowering of blow-by and reduction in wear of the piston rings and cylinder walls. The final compression readings were higher and the ring gap increases were substantially lower. These tests indicate that the desired plateau finish for the piston rings and cylinders will give quicker ring seating with better oil control and reduction in blow-by from improved ring sealing action.

In the production of the controlled, plateau finish with the Flex-Hone tool, it is maintained in rotating condition at all times the honing device is in contact with the surface being honed. In honing a cylinder bore, for example, the honing device is maintained rotating as it is inserted and removed from the bore to provide a uniform surface throughout without tapering the sur face.

It is generally assumed that the major damage to bearings is caused during the first 10, 15 or 20 seconds after an engine is started from a cold start before thin film or full film lubrication is reached. In the above description it was established that the effect of "bearing" or load pressure is not only involved in the squeezing action on the oil but also the heat-causing factor and that oil drains from a "smooth surface" or from a surface that has only porosity. These concepts are also directly applicable to the facing of bearings for the same reasons. In addition valve guides and any two sliding coacting surfaces can be so treated. This should provide the desired bearing surface and provide a reservoir or lubricant at all times to minimize the aforementioned major cause of damage to bearings and the like.

It should now be evident to those skilled in the art, that the above teachings lead to improved operation and efficiencies of two coacting surfaces sliding or rotating over one another under pressure. Each of the surfaces is finished with a controlled plateau surface of 60 to 80 percent and with a crosshatch lubricant-retaining pattern. The crosshatch is defined to be substantially smooth with uniform cuts in both directions of approximately 45 degrees.

WHAT I CLAIM IS: 1. A method of preparing two pieces of material to finish them to a required size when they are to be used in sliding contact that is produced by relative movement of the materials while working under pressure, the method including the steps of: providing the two pieces of material with a required configuration and with mating surfaces finished so as to permit relative sliding movement between them; and flexibly finish honing each of the mating surfaces to provide each with a plateaued finish having a crosshatch pattern comprising a plurality of substantially similarly directed uniform grooves in two sets extending in two different directions angularly related to each other and also angularly related to a reference plane substantially perpendicular to the direction of the said relative movement between the two pieces of material.

2. A method according to claim 1 wherein the finish honing is performed with a honing tool having abrasive elements secured to a resilient base.

3. A method according to claim 1 or claim 2 wherein the two pieces of material comprise a piston-cylinder unit, the piston carrying at least one piston ring coacting with the internal wall of the cylinder.

4. A method according to any preceding claim wherein the crosshatch pattern has substantially smooth, uniform cuts in both directions disposed at substantially approximately 45 degrees.

5. A method according to claim 3 or claim 4 wherein the finishing of each surface is accomplished by rotating a honing device having a resilient base over the surfaces to be finished and maintaining the honing device in rotating condition at all times that it is in contact with each surface.

6. A method according to any of claims 3 to 5 wherein the bore of the cylinder is flexibly finish honed to provide a plateaued area of from 60 to 80 percent of the surface to form a bearing surface for a piston ring or rings carried by the piston, and wherein the face of a p

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. face. It is generally assumed that the major damage to bearings is caused during the first 10, 15 or 20 seconds after an engine is started from a cold start before thin film or full film lubrication is reached. In the above description it was established that the effect of "bearing" or load pressure is not only involved in the squeezing action on the oil but also the heat-causing factor and that oil drains from a "smooth surface" or from a surface that has only porosity. These concepts are also directly applicable to the facing of bearings for the same reasons. In addition valve guides and any two sliding coacting surfaces can be so treated. This should provide the desired bearing surface and provide a reservoir or lubricant at all times to minimize the aforementioned major cause of damage to bearings and the like. It should now be evident to those skilled in the art, that the above teachings lead to improved operation and efficiencies of two coacting surfaces sliding or rotating over one another under pressure. Each of the surfaces is finished with a controlled plateau surface of 60 to 80 percent and with a crosshatch lubricant-retaining pattern. The crosshatch is defined to be substantially smooth with uniform cuts in both directions of approximately 45 degrees. WHAT I CLAIM IS:

1. A method of preparing two pieces of material to finish them to a required size when they are to be used in sliding contact that is produced by relative movement of the materials while working under pressure, the method including the steps of: providing the two pieces of material with a required configuration and with mating surfaces finished so as to permit relative sliding movement between them; and flexibly finish honing each of the mating surfaces to provide each with a plateaued finish having a crosshatch pattern comprising a plurality of substantially similarly directed uniform grooves in two sets extending in two different directions angularly related to each other and also angularly related to a reference plane substantially perpendicular to the direction of the said relative movement between the two pieces of material.

2. A method according to claim 1 wherein the finish honing is performed with a honing tool having abrasive elements secured to a resilient base.

3. A method according to claim 1 or claim 2 wherein the two pieces of material comprise a piston-cylinder unit, the piston carrying at least one piston ring coacting with the internal wall of the cylinder.

4. A method according to any preceding claim wherein the crosshatch pattern has substantially smooth, uniform cuts in both directions disposed at substantially approximately 45 degrees.

5. A method according to claim 3 or claim 4 wherein the finishing of each surface is accomplished by rotating a honing device having a resilient base over the surfaces to be finished and maintaining the honing device in rotating condition at all times that it is in contact with each surface.

6. A method according to any of claims 3 to 5 wherein the bore of the cylinder is flexibly finish honed to provide a plateaued area of from 60 to 80 percent of the surface to form a bearing surface for a piston ring or rings carried by the piston, and wherein the face of a piston ring to be used in coacting relationship with the thus finished cylinder bore is flexibly finish honed to provide a plateaued area and crosshatch pattern substantially the same as defined for the finished bore.

7. A unit comprising two pieces of material wherever prepared by a method according to any preceding claim.

8. A unit according to claim 7 wherein the two pieces comprise a cylinder and a piston having at least one piston ring.

9. A method of preparing two pieces of material substantially as herein described.