Diesel Locomotive Technology

The Diesel Locomotive

The modern diesel locomotive is a self contained version of the electric locomotive.  Like the electric locomotive, it has electric drive, in the form of traction motors driving the axles and controlled with electronic controls.  It also has many of the same auxiliary systems for cooling, lighting, heating, braking and hotel power (if required) for the train.  It can operate over the same routes (usually) and can be operated by the same drivers.  It differs principally in that it carries its own generating station around with it, instead of being connected to a remote generating station through overhead wires or a third rail.  The generating station consists of a large diesel engine coupled to an alternator producing the necessary electricity.  A fuel tank is also essential.  It is interesting to note that the modern diesel locomotive produces about 35% of the power of a electric locomotive of similar weight. 

Parts of a Diesel-Electric Locomotive

The following diagram shows the main parts of a diesel-electric locomotive. 

Diesel Engine

This is the main power source for the locomotive.  It comprises a large cylinder block, with the cylinders arranged in a straight line or in a V.  The engine rotates the drive shaft at up to 1,000 rpm and this drives the various items needed to power the locomotive.  As the transmission is electric, the engine is used as the power source for the electricity generator or alternator, as it is called nowadays.

Main Alternator

The diesel engine drives the main alternator which provides the power to move the train.  The alternator generates AC electricity which is used to provide power for the traction motors mounted on the trucks (bogies).  In older locomotives, the alternator was a DC machine, called a generator.  It produced direct current which was used to provide power for DC traction motors.  Many of these machines are still in regular use.  The next development was the replacement of the generator by the alternator but still using DC traction motors.  The AC output is rectified to give the DC required for the motors.

Auxiliary Alternator

Locomotives used to operate passenger trains are equipped with an auxiliary alternator.  This provides AC power for lighting, heating, air conditioning, dining facilities etc. on the train.  The output is transmitted along the train through an auxiliary power line.  In the US, it is known as "head end power" or "hotel power". In the UK, air conditioned passenger coaches get what is called electric train supply (ETS) from the auxiliary alternator.  

Motor Blower

The diesel engine also drives a motor blower.  As its name suggests, the motor blower provides air which is blown over the traction motors to keep them cool during periods of heavy work.  The blower is mounted inside the locomotive body but the motors are on the trucks, so the blower output is connected to each of the motors through flexible ducting.  The blower output also cools the alternators.  Some designs have separate blowers for the group of motors on each truck and others for the alternators.  Whatever the arrangement, a modern locomotive has a complex air management system which monitors the temperature of the various rotating machines in the locomotive and adjusts the flow of air accordingly.

Air Intakes

The air for cooling the locomotive's motors is drawn in from outside the locomotive.  It has to be filtered to remove dust and other impurities and its flow regulated by temperature, both inside and outside the locomotive. 

Rectifiers/Inverters

The output from the main alternator is AC but it can be used in a locomotive with either DC or AC traction motors.  DC motors were the traditional type used for many years but, in the last 10 years, AC motors have become standard for new locomotives.  They are cheaper to build and cost less to maintain and, with electronic management can be very finely controlled. 

Electronic Controls

Almost every part of the modern locomotive's equipment has some form of electronic control.  These are usually collected in a control cubicle near the cab for easy access.  The controls will usually include a maintenance management system of some sort which can be used to download data to a portable or hand-held computer.

Control Stand

This is the principal man-machine interface, known as a control desk in the UK or control stand in the US.  The common US type of stand is positioned at an angle on the left side of the driving position and, it is said, is much preferred by drivers to the modern desk type of control layout usual in Europe and now being offered on some locomotives in the US.

Cab

The standard configuration of US-designed locomotives is to have a cab at one end of the locomotive only. Since most the US structure gauge is large enough to allow the locomotive to have a walkway on either side, there is enough visibility for the locomotive to be worked in reverse. However, it is normal for the locomotive to operate with the cab forwards. In the UK and many European countries, locomotives are full width to the structure gauge and cabs are therefore provided at both ends.

Batteries

Just like an automobile, the diesel engine needs a battery to start it and to provide electrical power for lights and controls when the engine is switched off and the alternator is not running.

Pinion/Gear

The traction motor drives the axle through a reduction gear of a range between 3 to 1 (freight) and 4 to 1 (passenger).

Fuel Tank

A diesel locomotive has to carry its own fuel around with it and there has to be enough for a reasonable length of trip.  The fuel tank is normally under the loco frame and will have a capacity of say 1,000 imperial gallons (UK Class 59, 3,000 hp) or 5,000 US gallons in a General Electric AC4400CW 4,400 hp locomotive.  The new AC6000s have 5,500 gallon tanks.  In addition to fuel, the locomotive will carry around, typically about 300 US gallons of cooling water and 250 gallons of lubricating oil for the diesel engine.

Air ReservoirsAir reservoirs containing compressed air at high pressure are required for the train braking and some other systems on the locomotive.  These are often mounted next to the fuel tank under the floor of the locomotive.

Air Compressor

The air compressor is required to provide a constant supply of compressed air for the locomotive and train brakes.  In the US, it is standard practice to drive the compressor off the diesel engine drive shaft.  In the UK, the compressor is usually electrically driven and can therefore be mounted anywhere.  The Class 60 compressor is under the frame, whereas the Class 37 has the compressors in the nose.

Drive Shaft

The main output from the diesel engine is transmitted by the drive shaft to the alternators at one end and the radiator fans and compressor at the other end. 

Gear Box

The radiator and its cooling fan is often located in the roof of the locomotive.  Drive to the fan is therefore through a gearbox to change the direction of the drive upwards.

Radiator and Radiator Fan

The radiator works the same way as in an automobile.  Water is distributed around the engine block to keep the temperature within the most efficient range for the engine.  The water is cooled by passing it through a radiator blown by a fan driven by the diesel engine. 

Turbo Charging

The amount of power obtained from a cylinder in a diesel engine depends on how much fuel can be burnt in it.  The amount of fuel which can be burnt depends on the amount of air available in the cylinder.  So, if you can get more air into the cylinder, more fuel will be burnt and you will get more power out of your ignition.  Turbo charging is used to increase the amount of air pushed into each cylinder.  The turbocharger is driven by exhaust gas from the engine.  This gas drives a fan which, in turn, drives a small compressor which pushes the additional air into the cylinder.  Turbocharging gives a 50% increase in engine power. The main advantage of the turbocharger is that it gives more power with no increase in fuel costs because it uses exhaust gas as drive power.  It does need additional maintenance, however, so there are some type of lower power locomotives which are built without it.

Sand Box

Locomotives always carry sand to assist adhesion in bad rail conditions.  Sand is not often provided on multiple unit trains because the adhesion requirements are lower and there are normally more driven axles.

Truck Frame

This is the part (called the bogie in the UK) carrying the wheels and traction motors of the locomotive. 

Classification of Diesel Locomotives

Locos, except for older steam ones, have classification codes that identify them. This code is of the form '[gauge][power][load][series][subtype][suffix]'

In this the first item, '[gauge]', is a single letter identifying the gauge the loco runs on:

W = Broad Gauge Y = Meter Gauge

Z = Narrow Gauge (2' 6")

N = Narrow Gauge (2')

The second item, '[power]', is one or two letters identifying the power source:

D = Diesel C = DC traction

A = AC traction

CA = Dual-power AC/DC traction

B = Battery electric(rare)

The third item, '[load]', is a single letter identifying the kind of load the loco is normally used for:

M = Mixed Traffic P = Passenger

G = Goods

S = Shunting

L = Light Duty (Light Passenger?) (no longer in use)

U = Multiple Unit (EMU / DEMU)

R = Railcar (see below)

The fourth item, '[series]', is a digit identifying the model of the loco. Until recently, this series number was simply assigned chronologically as new models of locos were introduced.

Brief History of Diesel Loco Shed, Itarsi

Diesel Loco Shed Itarsi was established in 1964 with beginning of loco holding 40 nos. It is now rated as one of the premier shed of Indian Railways.

The Diesel Loco Shed is now homing WDM‐2, WDM‐3A, WDM‐3D,WDP-4 and WDS‐6 class of Diesel Locomotives .The existing holding of the Shed is 171 locos, with a mail link of 97 Locos and goods outage target of 35 Locos. Now shed is ready to take the challenge of homing WDP‐4 (4000&4500HP Locos) GM locos.

A full‐fledged Chemical & Metallurgical Laboratory has been established in this shed. Two Effluent Treatment Plant & Incinerator are also available.

A Diesel Technical Training Centre for training the supervisors, artisans and operating/running staff is also functional in the Shed.

MAINTENANCE SHED

Main Types of Loco at shed

WDM2

2600 hp Alco models Co-Co, 16-cylinder 4-stroke turbo-supercharged engine. Introduced in 1962. The first units were imported fully built from Alco. After 1964, DLW produced this loco in vast numbers in lots of different configurations. This loco model was IR's workhorse for the second half of the 20th century, and perhaps the one loco that has an iconic association with IR for many people. These locos are found all over India hauling goods and passenger trains — the standard workhorse of IR. Many crack trains of IR used to be double-headed by WDM-2 locos; this has decreased now owing to the electrification of most important sections and the use of more powerful locos. A single

WDM-2 can generally haul around 9 passenger coaches; twin WDM-2's were therefore used for 18-coach trains.

WDM3A

These 3100hp locos are more powerful versions of the WDM-2. The first one was delivered on August 22, 1994. A single WDM-3A could haul a 21-coach passenger train, something that required two of the older WDM-2's. The WDM-3A also has a rated top speed of 120km/h, Early units were air-braked but lately many have been provided dual-braking capability. Dynamic brakes are also provided. The loco has a single cab. Gear ratio 65:18 as with the WDM-2. All recent units have a square profile, but a few early versions have a rounded appearance.

WDM3D

A higher-powered version of the basic WDM-2C (WDM-3A) class, these locos have a 3300hp powerpack, with available traction power of 2925hp. The engine is an enhanced version of the 16-cylinder Alco 251C model.

Max. speed 160km/h. Fabricated (welded) Alco High-Adhesion Co-Co bogies. Starting TE is 36036kgf (353kN). Dual braking systems.

WDS6

Heavy-haul shunters made in large numbers for industrial concerns as well as for IR, starting in 1975. These locos consist of the YDM-4 powerpack (6-cylinder 4-stroke inline Alco engine, turbo-supercharged) placed on WDM-2 frames. Same bogies as the WDM-2, WAM-4, WCAM-1 locos (Alco cast asymmetric trimount bogies). 1200/1350hp net (1400hp gross). Max. speed 62.5km/h. Several of them have a so-called 'creep control' system which allows them to be operated at a sustained speed of between 1 to 7 km/h for hauling special or heavy loads.

WDP–4

These are 4000hp locos with the 16-cylinder EMD 16-710 (16-V-710G3B-EC) turbocharged engines (AC-AC transmission) with unit fuel injection. The fabricated underframe has a rigid design. The bogies are GM's light-weight cast HTSC bogies similar to those of WDG-4 locos but meant for passenger use. The bogies are said to have a 'million mile' overhaul interval because of a reduction in the number of wearing surfaces. The suspension is a two-stage suspension. They have an interesting Bo1-1Bo wheel arrangement. Max. speed 160km/h, although in trials it is said to have been run at speeds up to 180km/h. However, in most cases today [2/05] the loco is restricted to 110km/h or so since it used for hauling heavier 24-coach passenger trains. The EM2000 onboard microprocessor system provides a flexible and expandable control system with complete self-diagnostic and unit history features. The cab body is made of fibreglass.

Bogie Parts & Description

Introduction

The bogie, or truck as it is called in the US, comes in many shapes and sizes but it is in its most developed form as the motor bogie of an electric or diesel locomotive or an EMU.  Here it has to carry the motors, brakes and suspension systems all within a tight envelope.  It is subjected to severe stresses and shocks and may have to run at over 300 km/h in a high speed application.

Fig. A bogie of diesel locomotive

Association of American Railroads classification deals with classification of locomotives based on wheel arrangement. This classification is explained below under two heads :

1. Classification of wheels.2. Arrangement of wheels in loco.

1. Classification of wheels

There are two types of wheels

i. Carrying wheels

Carrying wheels are only for carrying the weight of loco and do not have driving power. They are denoted by numbers 1,2,3 and so on.

1- One set of carring wheels , 2- two set of carring wheels and like wise.

ii. Driving wheels

They are for carrying as well as driving the loco. They are denoted by letter A,B,C and so on. They are of two types :

a) Independent driving wheel - Denoted by adding suffix ‘O’ with denoting letter. For example, AO represents one set of driving wheel, BO represents two sets of driving wheels and like wise.

b) Coupled driving wheel – denoted by dash to denoting letters. For example, A’ represents one set of coupled wheels and like wise.

2. Arrangement of wheels in locomotive

i. Rigid frame loco

In this wheel arrangement, chassis is directly mounted on wheel. These are represented in single block.

ii. Bogie type loco

In this first wheel are arranged into bogie and then chassis is mounted on bogie. It provides greater flexibility than rigid frame arrangement for negotiating curves. Represented by two blocks separated by ‘-’ sign.

Types of bogie

A. Trimount bogie - rigid bolster swivel type, used in WDM2 loco.B. High adhesion high speed bogie (HAHS) – used in WDM 3D loco.

C. High tensile steel casted bogie (HTSC) – used in GM loco.

D. Adhesion tensile hish speed (ATHS) trimount bogie – used in WDM 3A loco.

Parts of a bogie

Bogie Frame

Can be of steel plate or cast steel.  In this case, it is a modern design of welded steel box format where the structure is formed into hollow sections of the required shape.

Bogie Transom

Transverse structural member of bogie frame (usually two off) which also supports the carbody guidance parts and the traction motors.

Brake Cylinder

An air brake cylinder is provided for each wheel.  A cylinder can operate tread or disc brakes.  Some designs incorporate parking brakes as well.   Some bogies have two brake cylinders per wheel for heavy duty braking requirements.  Each wheel is provided with a brake disc on each side and a brake pad actuated by the brake cylinder.  A pair of pads is hung from the bogie frame and activated by links attached to the piston in the brake cylinder.  When air is admitted into the brake cylinder, the internal piston moves these links and causes the brake pads to press against the discs.  A brake hanger support bracket carries the brake hangers, from which the pads are hung.

Primary Suspension Coil

A steel coil spring, two of which are fitted to each axlebox in this design.  They carry the weight of the bogie frame and anything attached to it.

Motor Suspension Tube

Many motors are suspended between the transverse member of the bogie frame called the transom and the axle.  This motor is called "nose suspended" because it is hung between the suspension tube and a single mounting on the bogie transom called the nose.

Gearbox

This contains the pinion and gearwheel which connects the drive from the armature to the axle.

Lifting Lug

Allows the bogie to be lifted by a crane without the need to tie chains or ropes around the frame.

Traction Motor

Since the diesel-electric locomotive uses electric transmission, traction motors are provided on the axles to give the final drive.  These motors were traditionally DC but the development of modern power and control electronics has led to the introduction of 3-phase AC motors.   There are between four and six motors on most diesel-electric locomotives.  A modern AC motor with air blowing can provide up to 1,000 hp. Normally, each axle has its own motor.  It drives the axle through the gearbox.  Some designs, particularly on tramcars, use a motor to drive two axles.

Neutral Section Switch Detector

The overhead line is divided into sections with short neutral sections separating them.  It is necessary to switch off the current on the train while the neutral section is crossed.  A magnetic device mounted on the track marks the start and finish of the neutral section.  The device is detected by a box mounted on the leading bogie of the train to inform the equipment when to switch off and on.

Secondary Suspension Air Bag

Rubber air suspension bags are provided as the secondary suspension system for most modern trains.  The air is supplied from the train's compressed air system.

Wheel Slide Protection System Lead to Axlebox

Where a Wheel Slide Protection (WSP) system is fitted, axleboxes are fitted with speed sensors.  These are connected by means of a cable attached to the WSP box cover on the axle end.

Loose Leads for Connection to Carbody

The motor circuits are connected to the traction equipment in the car or locomotive by flexible leads shown here.

Shock Absorber

To reduce the effects of vibration occurring as a result of the wheel/rail interface.

Axlebox Cover

Simple protection for the return current brush, if fitted, and the axle bearing lubrication.

A typical journal bearing

Dampers

A damper is said to have failed, if there is no resistance to movement in compression, in rebound or in both directions and a simple manual test can detect the failure. Besides that heavy leakage of oil is also a sign of failure of damper.

A vertical damper

Wheel And Axle Inspection

Inspect wheels for thin and damaged flanges, broken rims, cracks, flat spots, or any other obvious defects, in accordance with applicable rules and regulations. Check wheels for thermal cracking or other evidence of overheating. If thermal cracking or an overheating condition has occurred, true the wheels in accordance with this section of the maintenance manual. Inspect and check the wheel flange height, flange thickness, and wheel tread using an approved wheel gauge as required.

Wheels should be inspected for any visible defects before and/or after each trip. Wheels should be periodically checked for wear, sharp flanges, shelling, cracks, and flat spots to see that they are within the limits of the appropriate governing authority .

Wheel Defects

All wheels and axles that enter the wheel shop should be inspected for defects mentioned below. Any wheel and axle with a defect that cannot be rectified by machinery within the prescribed tolerances should be scrapped. Wheel defects are given below:

1.Burnt Rim

If a portion of flange or rim breaks off, wheel must be removed from service. Rough granular fracture is seen; this is caused due to overheating of wheel during manufacture.

2. Shattered Rim

The wheel that shows a circumferential crack on the front or back face of the rim must be removed from service.

3. Spread Rim

Spreading of the rim is usually accomplished by a flattening of the tread and may or may not have cracks or shelling on the tread. If the rim widens out for a short distance on the front face, an internal defect may be present and the wheel must be withdrawn from service.

4. Subsurface Defect

If voids or a lamination or flaky condition is disclosed under the surface while turning a wheel, the wheel has a sub-surface defect. Unless this defect has progressed too far it can generally be removed by turning of wheel further taking care that all evidence of defect is eliminated before putting such wheels in service.

5. Shelled Tread The wheel has a shelled tread when pieces of metal break out. Such wheel must be removed from service unless this defect has progressed too far, it can generally be removed by turning

of wheel further taking care that all evidence of the defect is eliminated before putting such wheels in service.

6. Thermal Cracks Intense heating caused by braking may result in thermal cracks. It is a serious defect and requires immediate removal of the wheel from service. Shallow thermal cracks can however, be removed by machining taking extra care to ensure that the crack has been completely eliminated in the operation. Wheels found with radial cracks on the back or front face of the rim should be removed from service. Spalling is the result of small portions of metal breaking out between or adjacent to fine thermal cracks which in turn may be associated with small skid marks. Spalling normally is not considered, as condemnable defect as it can be removed by machining the treads down to sound metal.

7. Slid Flat It occurs due to skidding of wheel. Slid flat is measured circumferentially in length and wheel should be machined to remove the slid flat of 50 mm or more.

8. Cracked or Broken Flange The wheel should be condemned and must be removed from service when cracked or broken flange develops.

9. Cracked or Broken Plate Cracks in the plate develop due to severe service loads and braking condition in combination with internal stresses in the wheel and possibly surface defects in areas subject to high stresses. Most plate cracks are progressive in nature and it is important that they be detected in the early stages and removed from service. An examination of this fracture would be necessary to make sure that it did not originate as a thermal crack.

10. Loose Wheels Wheels must be removed from service if they show indications of being loose on the axle. This is usually indicated by oil on the back plate of the wheel or evidence of any wheel movement on the axle wheel seat.

Wear Limits of Wheels in a Bogie

Wheel Size Variation Limits The following limits apply to wheel diameters. The “new” values listed below are to be used when turning (truing or profiling) wheels in the shop. The “worn” values are to be used when inspecting locomotives to determine need for wheel turning.

Between two wheels on the same axle: New: 0.5mm

Between axles within a bogie: New: 2 mm Worn: 8 mm

Between bogies: New: 15 mm Worn: 25 mm

Evaluation of Cracks and Other Defects in a Bogie

1. The extent of crack shall be located by visual inspection with a magnifying glass (10x) followed by dye penetrant or magnetic particle test.

2. After marking out the full extent of the crack, arrestor holes of suitable size (minimum diameter10.0 mm) shall be drilled at least 25.0 mm away from the extremities of the crack.

3. The entire crack shall be eliminated by opening out the affected section right up to the bottom of the crack.

4. The removal of the defective area shall be resorted to by flame gouging/arc air gouging/pneumatic chipping followed by grinding with a portable pencil grinder.

5. The section thus opened out shall extend upto the arrestor holes. The open out section shall further be checked by DPT or MPT, to ensure freedom from any further cracks. 1.6 The areas containing other defects like shrinkage cavities and inclusions etc. if any shall also be located and marked and these defects shall be completely removed by flame gouging/arc air gouging/chipping before welding.

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