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A coupling rod or side rod connects the driving wheels of a locomotive. Steam locomotives in particular usually have them, but some diesel and electric locomotives, especially older ones and shunter locomotives, also have them. The coupling rods transfer the power of drive to all wheels.
Locomotion No. 1 was the first locomotive to employ coupling rods rather than chains. In the 1930s reliable roller bearing coupling rods were developed. [1]
In general, all railroad vehicles have spring suspension; without springs, irregularities in the track could lift wheels off the rail and cause impact damage to both rails and vehicles. Driving wheels are typically mounted so that they have around 1 inch (2.5 cm) of vertical motion. When there are only 2 coupled axles, this range of motion places only slight stress on the crank pins. With more axles, however, provision must be made to allow each axle to move vertically independently of the others without bending the rods. This may be done by hinging the side rod at each intermediate crank pin, either using the pin itself as a hinge pin, [2] [3] or adding a hinge joint adjacent to the pin, as shown in the illustration.
An alternative is to use a side rod that spans multiple axles with a scotch yoke used at each intermediate axle. This approach was quite common when side rods were used to link a jackshaft to 2 or more driving wheels on electric locomotives and some early internal combustion locomotives. The Swiss Ce 6/8II Crocodile locomotive is a prominent example, but there were others. [4] [5] [6]
The coupling rod's off-center attachment to the crank pin of the driving wheel inevitably creates an eccentric movement and vibration when in motion. To compensate for this, the driving wheels of an inside-frame locomotive always had built-in counterweights to offset the angular momentum of the coupling rods, as shown in the figures above. On outside-frame locomotives, the counterweight could be on the driving wheel itself, or it could be on the crank outside the frame, as shown in the adjacent figure.
Where the motion of the side-rods is purely circular, as on locomotives driven by jackshafts or geared transmission to one driver, counterweights can balance essentially all of the motion of the side rods. Where part of the motion is non-circular, for example, the horizontal motion of a piston rod, counterweights on the wheels or drive axles cannot be made to balance the entire assembly perfectly. On a driving wheel supporting both side-rods and the connecting rod to a piston, the counterweight needed to balance the horizontal motion of the piston and connecting rod would be heavier than the counterweight needed to balance the vertical weight of the rods. As a result, a counterweight chosen to minimize the total vibration will not minimize the vertical component of the vibration.
The vertical component of the vibration that could not be eliminated because of the weight needed to balance the pistons is called hammering. This is destructive to both the locomotive and the roadbed. In some locomotives, this hammering can be so intense that at speed, the drivers alternately jump from the rail head, then slam down hard on the rails as the wheels complete their rotation. Unfortunately, hammering is inherent to conventional two-cylinder piston-driven steam locomotives and that is one of the several reasons they have been retired from service.
Initially, coupling rods were made of steel.[ citation needed ] As technology progressed and better materials became available, the connecting rods were manufactured of lighter and stronger alloys [ citation needed ], which in turn permitted smaller counterweights and also reduced hammering.
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons. On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods ; normally one pair is directly driven by the main rod which is connected to the end of the piston rod; power is transmitted to the others through the side rods.
A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaft. The connecting rod is required to transmit the compressive and tensile forces from the piston. In its most common form, in an internal combustion engine, it allows pivoting on the piston end and rotation on the shaft end.
Main components found on a typical steam locomotive include:
The Walschaerts valve gear is a type of valve gear used to regulate the flow of steam to the pistons in steam locomotives, invented by Belgian railway engineer Egide Walschaerts in 1844. The gear is sometimes named without the final "s", since it was incorrectly patented under that name. It was extensively used in steam locomotives from the late 19th century until the end of the steam era.
The GWR 4100 Class was a class of steam locomotives in the Great Western Railway (GWR) of the United Kingdom.
The Scotch yoke is a reciprocating motion mechanism, converting the linear motion of a slider into rotational motion, or vice versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The location of the piston versus time is simple harmonic motion, i.e., a sine wave having constant amplitude and constant frequency, given a constant rotational speed.
Engine balance refers to how the inertial forces produced by moving parts in an internal combustion engine or steam engine are neutralised with counterweights and balance shafts, to prevent unpleasant and potentially damaging vibration. The strongest inertial forces occur at crankshaft speed and balance is mandatory, while forces at twice crankshaft speed can become significant in some cases.
A jackshaft is an intermediate shaft used to transfer power from a powered shaft such as the output shaft of an engine or motor to driven shafts such as the drive axles of a locomotive. As applied to railroad locomotives in the 19th and 20th centuries, jackshafts were typically in line with the drive axles of locomotives and connected to them by side rods. In general, each drive axle on a locomotive is free to move about one inch (2.5 cm) vertically relative to the frame, with the locomotive weight carried on springs. This means that if the engine, motor or transmission is rigidly attached to the locomotive frame, it cannot be rigidly connected to the axle. This problem can be solved by mounting the jackshaft on unsprung bearings and using side-rods or chain drives.
In rail terminology, hammer blow or dynamic augment is a vertical force which alternately adds to and subtracts from the locomotive's weight on a wheel. It is transferred to the track by the driving wheels of many steam locomotives. It is an out-of-balance force on the wheel. It is the result of a compromise when a locomotive's wheels are unbalanced to off-set horizontal reciprocating masses, such as connecting rods and pistons, to improve the ride. The hammer blow may cause damage to the locomotive and track if the wheel/rail force is high enough.
A lateral motion device is a mechanism used in some railroad locomotives which permits the axles to move sideways relative to the frame. The device allows easier cornering.
The Gölsdorf axle system is used on railway Gölsdorf locomotives to achieve quiet running and low wear-and-tear when negotiating curves. The axle system comprises a combination of fixed axles and axles that can slide transversely, all within a single, rigid locomotive frame. The system was invented by a young Austrian locomotive builder, Karl Gölsdorf, around the end of the 19th century. The first locomotive to use this principle entered service in 1897.
The Be 4/6 12302 was one of four test locomotives ordered by the Schweizerische Bundesbahnen (SBB) in June 1917, along with the Be 3/5 12201, Be 4/6 12301 and Ce 6/8I14201. It was intended to be used on the Gotthardbahn, in order to gain experience in ordering and operating electric locomotives, However, the Be 4/6 12302 was never used for scheduled services on the Gotthard, because at its introduction it was already outperformed by the successor class Be 4/6 12303-12342.
A steam motor is a form of steam engine used for light locomotives and light self-propelled motor cars used on railways. The origins of steam motor cars for railways go back to at least the 1850s, if not earlier, as experimental economizations for railways or railroads with marginal budgets. These first examples, at least in North America, appear to have been fitted with light reciprocating engines, and either direct or geared drives, or geared-endless chain drives. Most incorporated a passenger carrying coach attached to the engine and its boiler. Boiler types varied in these earlier examples, with vertical boilers dominant in the first decade and then with very small diameter horizontal boilers. Other examples of steam motor cars incorporated an express-baggage or luggage type car body, with coupling apparatus provided to allow the steam motor car to draw a light passenger coach.
A return connecting rod, return piston rod or double piston rod engine or back-acting engine is a particular layout for a steam engine.
The Central South African Railways Rack 4-6-4RT of 1905 was a South African steam locomotive from the pre-Union era in Transvaal Colony.
Steam springs or steam suspension are a form of suspension used for some early steam locomotives designed and built by George Stephenson. They were only briefly used and may have been used for fewer than ten locomotives.
The MÁV class 601 was a class of Hungarian four-cylinder Mallet locomotives, which was designed to haul long and very heavy cargo on very steep railway tracks. At 22.5 m long and outputting 2,200 kW (3,000 hp), they were the largest and most powerful steam locomotives built in Europe before and during World War I.
A slider-crank linkage is a four-link mechanism with three revolute joints and one prismatic (sliding) joint. The rotation of the crank drives the linear movement of the slider, or the expansion of gases against a sliding piston in a cylinder can drive the rotation of the crank.
Rigid-framed electric locomotives were some of the first generations of electric locomotive design. When these began the traction motors of these early locomotives, particularly with AC motors, were too large and heavy to be mounted directly to the axles and so were carried on the frame. One of the initial simplest wheel arrangements for a mainline electric locomotive, from around 1900, was the 1′C1′ arrangement, in UIC classification.
