Connecting rod

A connecting rod, connecting rod also, push rod or drive rod, at a crank drive motor and machines is the connection between the crankshaft and the crank pin and is located in reciprocating motion piston or crosshead. The connecting rod is the linear motion of the power or working piston into the circular motion of the crankshaft (linear oscillating axial movement ), or conversely, a circular to linear motion in order.

Similar facilities are there in the skeleton of vertebrates, but only circular arc parts are of course converted into linear motion ( see, for instance Os quadratum ).

The grammatical gender of " connecting rod " is by Duden and other German dictionaries male ( the connecting rod ), in the technical field, the word is also used as neuter ( connecting rod ). This Genuszweideutigkeit can be bypassed with " the rod ".

• 4.1 cracking
• 4.2 Cutting / Sawing

Applications

Rods come in a wide variety of machine types used.

Bending punch

In a bending punch the connecting rod is used to implement the most overhead rotating unit to the most vertically -operated bending or punching device. Numerous articulated connecting rods have been established as a special feature in this sector, which make it possible to choose freely force and, within certain limits and the machine stroke the workpiece and the machining largely adapt.

Steam engine

Even with steam engines on steamships or other steam engines to find connecting rods, which are used to implement the linear piston motion into rotary motion of the crankshaft. The drive system of the locomotives, this component is referred to as the drive rod and has in most cases directly to the driving axle of the locomotive.

The early steam engines after Newcomen had not yet this element; they used at best a diversion by a lever and could therefore only drive -linear loads, such as reciprocating pumps. Only with the design of Watt was the connecting rod and later ( after the expiry of patent claims ) the crankshaft really moving into the technology of steam engines.

Compressor

The connecting rod of a reciprocating compressor transmits the rotating force acting components of the crankshaft to the reciprocating piston to generate the compression.

Art linkage

The art boom in mining is based on the invention of the crooked pin ( connecting rod ), with which one could first convert rotary motion into linear.

Sewing machine

Connecting rod for a sewing machine may be used to implement the rotating movement of the drive into a vertical movement of the sewing needle. Historical driven by human power sewing machines used a connecting rod contributes to the implementation of the tilting movement of the footplate into the rotary motion of the drive axle.

Internal combustion engine

The connecting rod of a reciprocating piston internal combustion engine, for example, by Nicholas Otto ( four-stroke method) transmits the second and third clock of the working process, the gas forces in the cylinder chamber on the crankshaft, and uses the power of the crank shaft in the other two bars for expelling the exhaust gas, and fresh gas aspirate (see Otto engine ). In addition, the piston must quickly accelerated and decelerated again ( at 6000 U / min takes a stroke of 1/200 s - 5 ms). In this case, the connecting rod transfers the significant acceleration forces. For two-stroke engines a connecting rod with an undivided lower bearing ( connecting rod ) and a built crankshaft is usually used. There also swirled the sucked mixture and throws oil on the liner, in special fishing bags and to the crankshaft bearings.

For each piston part - apart from the free-piston engines - a connecting rod as coupling member between the oscillation of the piston and the rotation of the crankshaft. Two connecting rod to a piston there is the engine of the Honda NR models with oval pistons, press the two connecting rods side by side, and in diesel engines manufacturer Neander engine with two contra-rotating crankshafts, connecting rods, both of which act on a piston.

Of a different nature is the use of the push rods in the engine at Albert harvester ULTRAMAX control, which has become known in the motorcycle models NSU Max, Superfox and Maxi, and in the twin-cylinder engines of the car model NSU Prinz; serve two push rods ( with 90 ° phase shift ) to drive the camshaft.

Forms / Construction

There are rod bearings at both ends ( connecting-rod, connecting rod ) of the I-shaped, usually shaped connecting rod shank. On smaller connecting rod of the piston pin is inserted.

On larger connecting rod (or connecting rod ) is split connecting rod usually with two glands, the gland specific expansion bolts are normally used. The Verschraubungsprinzip the differential thread will be described in the literature, is almost never found in practice, however.

One-piece connecting rod big end caps removable without cause dismountable crankshafts. They are found in small appliances and some motorcycle engines.

To shorten the length of V-engines are separated " Anlenkpleuel " is used. Kinematically Since in this case due to receive the cylinder banks is not the same stroke, the compression may have to be balanced with different piston, otherwise additional vibrations occur.

Connecting rods must be designed for the high stress in their geometry on fatigue strength.

Materials

Materials commonly used for connecting rods today are C70 or micro-alloyed steels and sintered metals. For special applications, such as the motor sports area special quenched and tempered steels or due to the lower weight and titanium are used. Continue to be used even connecting rods made ​​of cast iron.

Production

Großserienpleuel be forged or sintered. Forged connecting point towards Sinterpleueln a better ratio of strength to weight at lower costs, but the die - making is very expensive and only worthwhile for large series. In large engines the connecting rods are forged or cast. In small series, the connecting rods are made from machined metal pieces.

Cracking

Cracked connecting rods are only made ​​in one piece, then with breaking notches ( Sinterpleuel ) or with a laser notch ( steel connecting rods ) provided and then deliberately broken into two parts ( cracking). Both parts are screwed in Pleuelmontage and fit perfectly together. Connecting rod and connecting rod cap must be based on the individual fracture geometry always remain together, the components are not separately replaceable. The fracture surfaces are advantageous in terms of strength, cost and production accuracy. The separation surfaces are almost not visible after assembly. It is an exact seat guaranteed and also the power transmission / forwarding is not interrupted as two separately manufactured parts.

1992 BMW V8 engine in the M60 for the first time Crackpleuel used in steel. Currently cracked steel connecting rods are introduced worldwide.

See also fracture separation.

Cutting / Sawing

Other methods of separation of the connecting rod ( saws followed by milling, grinding, if necessary, of the separation surfaces ) and mounting ( fitting bolts or dowels ) are only employed for small series or very large connecting rod ( truck, marine diesel, etc. ) are used.

Other General and Special

Previously had - especially with motorcycle engines to save a lubricating oil pump - also bearings in the connecting rod -used construction methods, as the upper connecting rod bearings often in the form of needle bearings. In larger and more modern constructions plain bearings dominate.

Two steel - lead bronze or steel-aluminum half-shells are placed in internal combustion engines in the large eye on the big end. The bearings are today highly complex components. Upper and lower bearing shell are due to the different load no longer symmetrical. Due to the enormous progress in the development of materials with very thin-walled bearing defined lubricating films have become possible in the micron range. Lugs on the half-shells are used for positioning and fixing of the bearing during installation. Contrary to the still widespread opinion, the lugs do not serve as a safeguard against slipping and twisting. The interference fit of the bearing shells is carried out by the surface pressure, which received the bearings when the bearing caps are screwed. In the top end bearing is often in a one-piece bronze bushing. These sockets are made of a steel jacket to which a sintered bronze is applied. Sockets in the top end bearing are only required in highly loaded connecting rods, for example, in diesel engines. Currently, the use of lead-free stock is advancing rapidly.

Overlays of non-ferrous metals must be lubricated and cooled by oil during operation: a connecting rod bearing damage is almost always the result of damage to the oil shortage. Before connecting rods were oil supplied through the drilled crankshaft first in the great big end to oil supply, from there, was fed via an internal bore in the connecting rod to the piston pin bearing lubricating oil. Recent simulation techniques have led to new designs of engines here, which could account for many oil wells. In the two- stroke engine and older small four-stroke engines, the storage is done by needle or roller bearings with lube oil supply is usually done only by spin - or mixture lubrication.

The fits in connecting rod bearings are dimensioned so that the predicted hot condition there is little lubrication column, from which the oil can escape. The desired lubrication technology in the connecting rod is that of a hydrodynamic journal bearing, ie from the orbital motion of the connecting rod is built up by the friction of movement entrainment of an oil cushion, which provides pure fluid friction with the right sizing and a wearable metal to metal contact is reliably prevented. When the piston pin bearing, however, no orbital motion is possible; in this storage is expected to mixed friction between the piston pin and small end bearing and, accordingly, the generous storage areas, pressures and oil flow rates are to be provided.

When the connecting rod is not running shared, so the connecting rod consists of only one part, must be to enable the assembly, the crankshaft from several mounted devices consist ( " constructed " ), that is, the crankshaft journal must be bolted or disassembled in any other way, and again can be mounted (presses, heat shrink ) ( Hirth coupling ), or a one-sided offset exhibit, with only one crank arm instead of both sides of the connecting rod.

The connecting profile of the connecting rod is typically an H- or I- profile. In racing engines of the fifties and sixties, there were also so-called knife - connecting rod with a slender diamond cross-section in the middle ( line connecting the two eyes) were thick and through sharp-edged at the sides: these connecting rods were advantages in the gas transport movements of two-stroke engines attributed. For two-stroke of the piston base and the crank chamber is generally the pumping movement of the gas feed placed (see load change), it will focus on the crankshaft, the connecting rod and the piston lower side in the stream of fresh gas, which usually also move the fresh gases and the accompanying transferred quantities of lubricant.

In many V-engines - some like the Ford V- 4 engine have the same number of pistons, connecting rods and crank pins - act either two identical connecting rods on a crank pin in the crankshaft direction in succession ( the result is a slight offset of the cylinder), or one of the two connecting rod is designed as a fork and comprises the second, so that the second connecting rod engaging on the crank shaft between the fork opening. Then there is no longitudinal displacement of the cylinders in a row, and thus no additional tilting moments. This elaborate design is for example found in motorcycles from Harley- Davidson; the front V- cylinder is indeed angled towards the rear cylinder, but not laterally offset.

There is also another type of fork connecting rods: a connecting rod to a crankshaft throw, however, the connecting rod Y-shaped forks up to it to carry two piston: A piston running normally, piston and connecting rod each with a round hole, the other eye also round, but the piston with a slot - freedom of movement of the second piston pin. This design was used from the twenties in Puch for a so-called dual-piston engine in the two-stroke principle, but later replaced by an articulation or Nebenpleuelkonstruktion. The advantage of the double piston is in the staggered by lifting movements of the two pistons becoming possible asymmetry of the slot controls the gas exchange. The are significant disadvantages: cooling problems, the construction cost, and an unfavorably shaped double - common combustion chamber with long flame paths and relatively high consumption. Both fork and Anlenkpleuel utilizing asymmetric timing, can be found in Puch motorcycles early twenties to late sixties. Between the end of the forties and mid-fifties of the Triumph -Werke Nürnberg were bifurcated into connecting rod parallel to the crankshaft axis in motorcycles, which, however, can realize any asymmetric timing.

Another alternative is the use of a third eye Hauptpleuels with laterally next to the crank -pin hole, in which engages a shorter auxiliary connecting rod. Disadvantage of this technique: this is a mechanical vibration coupling mechanism with highly complex geometrical description of the auxiliary connecting rod movement.

At the side of the radial engines access Hauptpleuel, depending on the number of cylinders, such as the nine-cylinder engine, up to eight auxiliary connecting rod.

History

The first known machine in which a rotary motion was implemented through connecting rod and crankshaft into linear motion, is the Roman Hierapolis sawmill (3rd century AD).