Piston and connecting rod assembly pdf

Retainer 90 includes amounting portion 92 having a circular perimeter. Mounting portion 92 includes a first surface 94 , a second surface 96 , two holes 95 between those surfaces, and a void therethrough. The void is sized so that the bearing portion 60 of the bearing insert 50 may be disposed through the void and the bearing insert 50 may nest within the retainer 90 with the second surface 56 of the mounting portion 52 of the bearing insert 50 contacting the first surface 96 of the mounting portion 92 of the retainer The nesting relationship of bearing portion 60 within the void of the mounting portion 92 of retainer 90 is indicated by the layout of elements in the assembly view of FIG.

Again referring to FIGS. Each bearing element is an arch-shaped member having two leg portions , a curved terminal region , and an inner surface The retainer 90 maintains a connection between the connecting rod 22 and the piston Specifically, inner surface within the curved terminal region of each bearing element provides a concave pivot surface on which the pivot projections 80 of the connecting rod 22 may pivot as the connecting rod 22 articulates with the piston It will be understood that in two-stroke combustion engines the retainer 90 will be unloaded during normal engine operation.

The function of the retainer 90 in such engines is to provide a down-stroke force linking the piston 20 to the connecting rod 22 at cranking and in failure modes that result in loss of cylinder pressure.

In four stroke engines, however, the retainer 90 will be loaded during normal engine operations and, therefore, the pivot surface may be surfaced with a suitable bearing material. That association of the bearing insert 50 and retainer 90 in the piston body 28 will be understood from the following description of the assembly of the various elements of the piston and connecting rod assembly The second end 74 of the connecting rod 22 is inserted into the void of the retainer 90 and is advanced through the void until each pivot projection 80 of the connecting rod 22 is nested within a curved terminal region of the retainer The connecting rod 22 and the retainer 90 are then disposed in the interior volume of the piston skirt 26 so that the second surface 96 of the mounting region 92 of the retainer contacts the piston skirt The bearing portion 60 of the bearing insert 50 is disposed through the void of the retainer and the bearing surface 62 of the bearing insert 50 contacts the bearing surface 76 of the connecting rod The piston crown 24 is then connected to the piston skirt 26 by threadedly engaging those members as described above, and the mounting portions 52 and 92 , respectively, of the bearing insert 50 and retainer 90 are captured between the piston crown 24 and piston skirt 26 to thereby retain the bearing insert 50 and the retainer 90 within the piston body 28 , and also maintain the connection of the retainer and the connecting rod In particular, it will be understood that the connecting rod 22 is trapped between the bearing surface 62 of the bearing insert 50 and the curved region of the retainer's 90 bearing elements In addition to the foregoing elements, assembly 10 also may include a separator in the form of a crown-to-insert separator plate shaped as a circular disk and having a plurality of bores therethrough.

The separator plate is disposed within the piston body between the first surface 54 of the bearing insert 50 and the inner surface 34 of the piston crown As shown in FIGS. The separator plate may be fabricated from a low weight and low thermal conductivity material, such as, for example, titanium, ceramic, and certain low thermal conductivity composite materials, that would reduce heat transfer from the piston crown 24 to the bearing insert Such materials will be readily apparent to those of skill in the art upon consideration of the present disclosure.

Lower heat transfer to the bearing insert 50 from the piston crown 24 would provide lower bearing insert and connecting rod temperatures, greater oil film thickness between the bearing surfaces 62 and 76 , and a consequent lower bearing wear rate at the interface between the bearing surfaces 62 and The separator plate is assembled into the assembly 10 by placing the separator plate onto the first surface 54 of the bearing insert 50 and then threadedly or otherwise connecting the piston crown 24 to the piston skirt The piston and connecting rod assembly 10 of the present invention provides a continuous pathway among its various elements for the circulation of liquids, such as, for example, engine oil, and gases.

The following discussion will refer to engine oil only, but it will be understood that the pathway may transport other liquids or gases. The engine oil enters the connecting rod 22 under pressure at port on the rod's second end 74 see FIG.

As shown in FIG. The recess 58 is sized so that the port opens into the recess 58 through the range of relative motion of bearing surface 62 and The delivery of engine oil to the bearing insert 50 will provide an oil film between the bearing surfaces 62 and The pressurized engine oil delivered to the recess 58 is forced through the two bores 64 which pass from the recess 58 into two of the radiating channels 58 on the first surface 54 of the bearing insert 50 , thereby cooling the bearing insert The engine oil then is forced from the channels 58 into overlying ports in the separator plate , which is disposed on the first surface 54 of the bearing insert 50 , and into the recess 38 a and channels 38 b on the inner surface 34 of the piston crown The separator plate may be constructed so as to initially direct the engine oil from the bearing insert 50 to the region within the piston crown 24 adjacent the piston ring grooves The recess 38 a and channels 38 b on the inner surface 34 also may be arranged so that the circulation of engine oil to the inner surface 34 begins at the region adjacent the piston ring grooves Arranging the engine oil circulation in that way provides the maximum cooling effect to the piston rings, resulting in lower ring temperatures and reduced piston ring wear rates.

In embodiments of the present invention lacking a separator plate , the engine oil may enter the recess 38 a and channels 38 b on the inner surface directly from the bearing insert, without passing through the intermediate separator element, but the separator plate provides the twin advantages of reducing heat transfer from the piston crown to the bearing surfaces 62 and 75 and providing an element that may be configured to advantageously direct the flow of engine oil to and from the piston crown Engine oil may exit from the recess 38 a and channels 38 b on the piston crown's inner surface 34 by passing through ports in the separator plate overlying the particular channel 58 on the first surface 54 of the bearing insert 50 that includes holes Holes 68 , in turn, are aligned with the holes 95 through the mounting portion 92 of the retainer 90 , and engine oil introduced into holes 68 at the ends of the central channel 58 is forced by pressure through holes 95 and into the interior cavity of the piston skirt 26 , where it may return to the engine oil sump and be recirculated throughout the engine.

The overlying arrangement of the central channel 58 , holes 68 , and holes 95 is illustrated in the sectional views of FIGS. If the assembly 10 lacks the separator plate , then the engine oil is forced by oil pressure from the cavity between the inner surface of the piston crown 24 the first surface 54 of the bearing insert, directly through the aligned 68 and 95 through the mounting portions of both the bearing insert 50 and retainer 90 , without having passed through the separator plate An alternate embodiment of the piston and connecting rod assembly of the present invention, generally designated as , is shown in FIGS.

The assembly also is particularly useful in two stroke internal combustion engines and may, for example, be incorporated into the piston, rod, and crankshaft assemblage of FIG. Assembly includes a piston and a connecting rod The piston includes a piston crown having a construction identical to that of piston crown 24 of the assembly The piston crown includes an inner surface and an exterior surface that may include annular piston ring grooves The inner surface includes a central recess a and circular channels b separated by projections c , which may be identical in design to the recess 38 a , channels 38 b , and projections 38 c , respectively, of the assembly Assembly also includes a cylindrical piston skirt defining a void therein.

Piston skirt includes an annular rim having threads on its exterior surface and which may be securely mated with annular threaded region on inner surface of the piston crown using the interference threaded connecting procedure described in connection with assembly It will be understood, however, that other means of securely connecting the piston crown and the piston skirt may be used, and certain other means of connection will be apparent to those of ordinary skill upon consideration of the present disclosure.

Assembly further includes a bearing insert having a disk-shaped mounting portion from which projects a bearing portion having a bearing surface The bearing portion has a cylindrical perimeter that is sized to fit within the void so that a surface of the mounting portion contacts the rim of the piston skirt , and the mounting portion is captured intermediate the piston crown and piston skirt when those elements are connected together.

The bearing surface is a concave region shaped as a region of sphere and, therefore, is defined by a spherical radius of curvature. The bearing insert also includes therethrough two generally centrally located bores , and further includes two bores that are located nearer the perimeter of the bearing insert First end includes a bearing surface that is a curved convex surface defined by a spherical radius of curvature having a region that will contact and articulate with a region of the concave bearing surface of the bearing insert Similar to assembly 10 , the articulation that may occur as between the bearing surfaces and provides a joint allowing relative movement between the connecting rod and the bearing insert , and ultimately between the connecting rod and the piston In order to retain the connecting rod and the piston together as a unit, the interior surface of the piston skirt includes two opposed mounting structures , each having a curved portion defining a concave pivot surface The connecting rod includes two projecting cylindrical structures defining pivot projections having central axis generally transverse to the longitudinal axis of the connecting rod's longitudinal axis.

Based on the description of assembly 10 above, it will be understood that each pivot projection is nested against a pivot surface to thereby retain the bearing surfaces and in contact while allowing for relative movement between the connecting rod and piston Piston of assembly also may include a separator between the inner surface of the piston crown and the bearing insert The separator may be in the form of a circular plate and includes several bores therethrough for passage of engine oil.

The separator may be constructed and provides the functions as described in connection with separator 50 of assembly In particular, the separator may be constructed to appropriately direct engine oil exiting under pressure through bores in bearing insert to the recess a and channels b formed on the inner surface of the piston crown Engine oil is channeled away from the piston crown through bores in the separator and into bores through the bearing insert , from which the engine oil may pass to the oil sump.

Thus, rather than including the retainer as a separate component, assembly incorporates elements of the retainer 90 of the assembly 10 into the piston skirt , which provides several advantages. Initially, there is a reduction in the number of parts, and the reduced parts number allows for ease of assembly and reduces the required parts inventories.

The construction of assembly also may provide a reduction in weight relative to assembly 10 , which is an important consideration in a reciprocating engine. In addition, assembly incorporates a spherically-shaped bearing surfaces and , allowing for the bearing surfaces to be manufactured in a non-location specific manner and without the need for locating the bearing surfaces rotationally. This reduces manufacturing cost and also reduces the sensitivity to machining tolerances for location of the bearing.

Although distinct embodiments of the present invention have been discussed above, it will be apparent that certain features of those embodiments may be variously combined to provide additional embodiments within the broader scope of the invention. For example, a piston and connecting rod assembly within the scope of the present invention may be provided with articulating connecting rod and bearing insert surfaces defined by a cylindrical radius of curvature as in assembly 10 and having a retainer integral with an inner surface of the piston skirt as in assembly As an additional example, a piston and connecting rod assembly of the present invention may include articulating connecting rod and bearing insert surfaces defined by a spherical radius of curvature as in assembly and a retainer that is a component separate from the piston skirt, piston crown, and bearing insert.

Advantages of the piston and connecting rod assembly of the present invention include the fact that a much larger piston to connecting rod bearing area may be attained compared with conventional designs including a piston pin. Another advantage is that the cooling channels may be naturally formed in the piston crown by the interface of the bearing insert or separator plate with the inner surface of the piston crown, thereby eliminating the need for cast-in cooling channels in the piston crown or complex machining arrangements.

Because the piston skirt does not carry conventional pin bosses, it is less susceptible to the asymmetric thermal expansion that may be experienced with such conventional designs. In conventional designs, asymmetric thermal loading results from the disparity in mass between the piston pin axis and the thrust plane. The thermal symmetry that may be achieved by the design of the present invention also is enhanced by the symmetric connection that may be provided between the piston crown and piston skirt.

In addition, the large bearing area that may be provided in the present invention between the piston and connecting rod as is provided, for example, between the articulating regions of bearing surfaces 62 and 76 in assembly 10 , and by bearing surfaces and of assembly also reduces the possibility of distortions due to gas pressure loading.

The engine piston is connected to the connecting rod with the help of a hollow hardened steel tube called wrist pin. It is also known as gudgeon pin. Wrist pin goes through the short end of the connecting rod and pivots on the engaged piston. The piston is connected to the crankshaft with the help of a connecting rod, which is usually shortened to the rod or Conrod.

The purpose of the piston is to work as a movable plug in the cylinder, which forms the bottom of the combustion chamber. Shell bearings have an adjustment for wear, but it controls the running and the side clearance allows the bearing cap to be tightened correctly. Construction and Functions of Connecting Rod There are two types of small end and big end bearings.

The big end is split at right angles to its length as at a or at an angle as at b , in order that it may be assembled on the crankpin. A cap is fixed to the body of the connecting rod by two bolts and nuts. Modern engines do not have bearing metal fused to the bore of a big end, but it uses separate low carbon steel bearing shells.

The shell bearing has adjustment for wear but gives the control over running and side clearance, providing the bearing cap to correct fit. Sometimes, thin pieces of metal known as shins are used when spur bearings are employed. These can be filled thinner to compensate for the wear of the bearing and also to secure the correct bearing clearance between the connecting rod and the crankshaft. The small end is usually a solid eye fitted with a phosphor bronze bush and a screw to close the eye around the pin.

All the connecting rods in an engine must be of equal weight otherwise noticeable vibration may occur. In the assembly, the connecting rods and caps are individually matched to each other. It usually carries identifying numbers so that they may not be mixed if the engine is dissembled for service. Types of Connecting Rod Following are the types of connecting rods, used in various types of engines:. Plain type rod 2. Fork and blade rod 3. Master and slave rod 4.

Split type rod 5. Billet conrods 6. Cast rods 7. Forged rods 8. Powered metal conrods. The plain type of connecting rods is used in inline and opposed engines. The big end of the connecting rod is attached to the crankpin and fitted with a bearing cap.

The bearing cap is mounted by a bolt or stud at the end of the connecting rod. The connecting rod must be replaced in the same cylinder and in the same relative position to maintain proper fit and balance. These types of connecting rods are used on V-twin motorcycle engines and V12 aircraft engines. In each pair of engine cylinders, a "fork" rod is divided into two parts at the big end and a "blade" rod is tapered from the opposing cylinder to fit this gap in the fork.

This system eliminates the rocking couple that occurs when the cylinder pairs are balanced along with the crankshaft. In the big-end bearings type of arrangement, the fork rod has a single wide-bearing sleeve that extends over the entire width of the rod, including the central gap. The blade rod then runs directly outside this sleeve, not on the crankpin. This causes the two rods to move back and forth, this reducing the force on the bearing and the surface speed.

But, the bearing speed also reciprocates instead of continuously rotating, which is a major problem for lubrication.

Radial engines typically use master-and-slave connecting rods. In this system, the one piston consists of a master rod with a direct attachment to the crankshaft. Other pistons connect their connecting rods to the rings surrounding the edge of the master rod.

The disadvantage of master-slave rods is that the stroke of the slave piston is slightly larger than that of the master piston, which increases the vibration in the V-type engine.

Billet connecting rods are designed from steel or aluminum. Compared to other types of connecting rods, they are lighter, stronger, and longer in lifespan. It is commonly used in high-speed vehicles. It is sometimes designed to reduce stress risers and ease into the natural grain of the billet material. These types of connecting rods are preferred and designed by manufacturers because they can capable of handling the load of a stock engine.

Cast rods require low cost to produce and cannot be used in applications of high horsepower. The cast rods have a noticeable seam in the middle that separates them from the forged type.

Some of the connecting rods are manufacture by forging. These types of connecting rods made by forcing a grain of material to the shape of the end. Depending on the required properties the material may be steel alloy or aluminum. Commonly used steel alloys are chrome and nickel alloy.

The end product is not designed to be brittle. Hence, nickel or chrome alloys increase the strength of the connecting rod. The piston shifts from one side of the cylinder to the other with sufficient force to produce a distinct noise. As the piston warms up the clearance is reduced and the noise usually disappears.

In order that fixed clearances may be used without risk of seizure special alloys have been introduced and many designs of the piston are in use. These special designs involved cam grinding to non-circular forms, semi-flexible skirts incorporating obliques slits, controlled distribution, and the like expedients. The piston head is usually flat but shaped to suit the combustion chamber. The combustion space can be controlled by dishing or doming the piston crown and recess for the valve heads can also be machined into the crown.

The compression ratio can be controlled by machining the combustion chamber in the piston, but it means that most of the heat of combustion has to be consumed through the piston instead of the cylinder head. The piston face that bears most heavily against the cylinder wall during the power stroke is called the major thrust face.

In some engines, the piston pin is offset from the centerline of the piston toward this face. If the piston pin is centered, the minor thrust face will remain in contact with the cylinder wall until the end of the compression stroke. But the connecting rod-angle changes from left to right as soon as the power stroke starts. This causes a sudden shift of the side thrust on the piston from the minor thrust face to the major thrust face.

If there is any appreciable clearance, a piston slap will occur. But if the piston pin is offset, the combustion pressure will cause the piston to tilt as the piston nears TDC, so that the lower end of the major thrust face will first make contact with the cylinder wall.

Then after the piston passes TDC and the reversal of the side thrust occurs, full major thrust face contacts are made with less tendency of the piston slap to occur. During operation, the piston runs many degrees hotter than the cylinder, because the cylinder is surrounded by cooling water.

Hence this piston expands more than the cylinder. This expansion must be controlled in order to avoid the loss of adequate piston clearance. Such a loss may cause serious engine trouble. The problem is more accurate with aluminum pistons because aluminum expands more rapidly than iron with the rise of temperature.

The expansion of the piston skirt can be controlled by several methods as follows. This can be done in the full-skirt piston by cutting horizontal slots in the piston just below the lower oil control ring groove.

These slots reduce the path for the heat traveling from the cylinder head to the skirt. Thus, the skirt does not become so hot and does not expand so much. In some full skirt pistons, vertical slots are also cut in the skirt, which would allow metal expansion in the skirt, with the appreciable increase of the piston diameter. The heat dam has a groove cut near the top of the piston.

This reduces the size of the path the heat can travel from the piston head to the skirt. The skirt, therefore, runs cooler and does not expand so much.

The pistons are finished so that they are slightly oval elliptical when cold. These pistons are called cam-ground pistons. Its area of contact with the cylinder wall therefore increases. The minor axis of the ellipse lies in the direction of the piston pin axis.

More expansion along the minor axis being caused by the piston bosses. The piston skirt is the cylindrical valve of the piston.

Piston skirts are made slightly rough at the time of manufacturing So that it can retain lubrication and also resist thrust. Thrust arises due to expansion stroke. The higher the piston length, the higher will be the skirt. This will give us a better bearing surface in the piston which will not make much engine noise. It is also called a gudgeon pin. The pin is used to connect the piston and connecting rod.

Harder steel is used as a material. The connecting rod connects the piston to the crankshaft, and this is functions as a liver arm and transfers motion from the piston to the crankshaft. The connecting rod is made of cast aluminum alloy. And it is designed in such a way that it can withstand the dynamic stresses of the combustion and piston movement. The bearing is installed in two parts and together they form a complete circle.

Bearing is installed between the connecting rod and the crank pin. The cap is the lower part of the piston assembly. The cap is the lower half of the connecting rod which forms the house for bearing the connecting rod.