Illustrated Encyclopedia of World Railway Locomotives

P. Ransome-Wallis

• Publisher: Dover Publications
• Year: 2013
• ISBN:
  9780486142760

In this volume, noted Columbia University Professor of Architecture Cyril M. Harris offers a unique tour through the entire history of architecture: an extraordinary compendium of clear, concise definitions for over 5,000 important terms. This thoroughly accurate and comprehensive gathering of architectural knowledge is complemented by an unprecedented collection of over 2,000 line drawings that richly illustrate significant aspects of architectural styles. Unusual cutaway views, close-ups of intricate details, and precisely rendered plans show many of the greatest architectural achievements of all time.
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CHAPTER 1

Diesel Railway Traction

by J. M. DOHERTY

Part I. Engines

BASIC REQUIREMENTS

The exacting and often conflicting nature of the demands made on diesel traction engines employed for main line railway service, present the engine builder with a number of difficult problems. Failure in service can cause severe dislocation to traffic, and in order to secure maximum availability the engine must be capable of working for long periods between overhauls with the minimum of attention. A high degree of robustness and durability is therefore required.

Service demands create wide fluctuations in speed and power output, and engines may be required to work at or near their maximum capacity for long periods. Furthermore, severe limitations of weight and space are often imposed. To facilitate overhaul and servicing, careful attention must be given to accessibility, and this is intimately linked with the general design of the locomotive or railcar in which the engine is to be installed.

For low-powered locomotives which are not subjected to severe weight limitations, a robustly constructed low-speed engine, naturally aspirated, is often preferred. An engine of this type gives exceptionally long life coupled with low maintenance costs. A more difficult problem arises in the case of engines required for intensive duty, and subjected to severe limitations with regard to space and weight, such as occur in high-powered diesel-electric locomotives. In these cases it has become necessary to adopt every available means for improving the power-weight ratio even when this entails an increase in cost and complication. The principal problem facing the engine builder is to meet these exacting requirements, without sacrificing reliability or unduly increasing operating expenses.

The following types of engines are employed for traction duty:

(i) Low-powered engines operating at 600–800 r.p.m. suitable for shunting (switching) and low-powered freight locomotives.

(ii) High-duty, low-speed engines, operating at 600–800 r.p.m. provided with pressure chargers (see page 31) and sometimes with intercoolers (see page 31), suitable for high-powered locomotives where ample space is available.

(iii) Moderate speed engines operating at 800–1,200 r.p.m. with or without pressure charging according to requirements, suitable for both moderate and high-powered locomotives.

(iv) Moderately powered, high-speed engines used for railcars, operating at 1,500–2,000 r.p.m sometimes provided with pressure charging.

(v) High-speed engines operating at 1,200–1,600 r.p.m. provided with pressure charging and intercooling. Used in high-powered locomotives and diesel trains of advanced design.

CONSTRUCTION

Camshafts may be one or two in number, depending on the design of the engine. The drive from the crankshaft is through a train of helical gears, or by means of a duplex roller chain incorporating a device which automatically maintains the chain tension. In addition to actuating the inlet and exhaust valves, the camshaft also drives the fuel pumps and engine governor.

Connecting rods are steel stampings or forgings, the small ends having bronze bushes, press fitted, working on floating gudgeon pins, which are prevented from moving endways in the pistons by means of circlips.

The crankcase forms the principal structural member of the engine, and must be very rigidly constructed to resist distortion and preserve the alignment of the crankshaft bearings. The bottom part is usually made separate from the upper part, being structurally integrated with it to form the engine bed, which incorporates the lower halves of the crankshaft bearing housings (Plate 1A, page 41).

Alternatively, the bottom part may act merely as an oil sump. With this type of construction the crankshaft is underslung, the upper halves of the bearing housings forming part of the upper portion of the crankcase (Plate 1E, page 41). Whichever type of construction is used, a rigid assembly is secured by locating the bearing caps sideways in the crankcase. Additional security is sometimes provided by means of cross ties consisting of long bolts which pass through the crankcase and bearing caps.

The cylinder blocks may be integral with the crankcase or form separate units attached by means of studs (Plate 1D, page 41). Crankcases are constructed of cast iron or aluminium alloy but for the larger type of engine an all-steel fabricated construction is often preferred, in which the transverse members are sometimes steel castings.

In the tunnel-type crankcase used both by Maybach and Saurer, the crankshaft is supported in roller bearings mounted on the crankshaft webs which are circular in shape. The crankcase is of cast iron or fabricated construction, and forms a tunnel-like structure surrounding the crankshaft, closed at the bottom by the oil sump. A short and stiff crankshaft can thus be incorporated in conjunction with a very rigid supporting system.

Another type of construction is used by Sulzer Bros, in which the fabricated crankcase is extended at one end to form a bed for the electric generator. The crankcase extends above the centre line of the crankshaft, and incorporates deep U-shaped bearing housings. Massive bearing caps are let into the housings and held firmly in position by the cylinder block, no studs being used.

Crankshafts are generally steel forgings, hardened and ground on the wearing surfaces, with separate balance weights bolted to the webs. A vibration damper is frequently mounted at the free end to damp out torsional vibrations. Four-, six- and eight-cylinder V-type engines are inherently unbalanced, and require the addition of secondary balancing systems, gear driven from the crankshaft.

Crankshaft and big-end bearings are usually of the steel-backed precision type, in which a thin layer of lead–copper bearing metal is backed by a steel shell. Such bearings, which do not require hand fitting, are non-adjustable and must be scrapped when worn. One of the crankshaft bearings is generally designed to locate the crankshaft endways, and is provided with thrust faces which bear against the webs of the adjacent cranks.

Cylinders up to eight in number may be arranged vertically (Plate 2, page 42) or horizontally in line, the latter type of construction being suitable for underfloor mounting in railcars. When more than this number of cylinders are required, the V-type of construction is generally adopted, the angle between the cylinder banks ranging from 45° to 90° (Plate 3, page 43).

The cylinders in the opposing banks may be staggered so that the two opposing connecting rods can work side by side on a common crank pin. This arrangement is used by English Electric, Mirrlees, Crossley, M.A.N., Daimler and Deutz. Alternatively, the cylinders in each bank may be in line with those in the opposite bank, thereby enabling the overall length of the engine to be reduced. When this is done the connecting rods are constructed on the fork and blade principle, or an articulated construction is adopted which causes the stroke of one piston to be slightly greater than the opposite one. The fork and blade construction is used by Paxman and Maybach, but most European builders employ the articulated arrangement.

By increasing the angle between the banks to 180° the horizontal twin bank engine is produced, which is suitable for underfloor mounting in high-powered rail-cars. The vertical twin bank engine developed by Sulzer has two parallel crankshafts driving the armature of the electric generator by means of step-up gearing so that it revolves at about 1½ times the engine speed.

The Napier Deltic engine, originally developed for fast motor-boats, consists of three banks of opposed piston two-stroke engines, arranged in the form of an inverted triangle, with the three crankshafts located at the corners. The connecting rods are of the fork and blade pattern. A train of gears is used to couple the three crankshafts together, and drive the main generator. The gear train also provides drives for the auxiliary generator, centrifugal type scavenger blower, fuel pumps, etc. (Plates 4 and 12A, pages 44 and 70).

Another type of opposed piston engine has been built by Fiat, in which there are four banks arranged in the form of a square with the crankshaft at the corners. Each bank contains four cylinders, and the crankshafts are coupled together by gearing.

Cylinder heads containing the fuel injector, inlet and exhaust valves, are made of cast iron or aluminium alloy, and are attached to the cylinder blocks by means of studs. When single inlet and exhaust valves are used, the inertia of the valves and valve operating mechanism may be considerable, particularly at high speeds. Most makers, therefore, provide two inlet and two exhaust valves per cylinder, when the bore exceeds seven inches. Maybach provide six valves per cylinder. The valve rocker gear for each cylinder is mounted on the cylinder head (Plate 1C, page 41).

Cylinder liners of hard, close-grained cast iron, often specially treated to reduce wear, are inserted in the cylinder blocks, where they are held firmly in position by the cylinder heads. Wet type cylinder liners are in direct contact with the cooling water, and at the lower end, a sealing ring prevents the leakage of water into the crankcase. Dry type cylinder liners are press fitted into circular housings formed in the cylinder blocks (Plate 1B and D, page 41).

Pistons which are cooled by oil under pressure are frequently constructed of cast iron. In most other cases aluminium alloy, which possesses good heat conducting properties, is used, and effectively dissipates the heat generated by combustion.

The pistons are provided with three or more cast iron piston rings which retain the compression and prevent leakage. In addition, two or more rings with oil retaining grooves are provided to distribute the lubricant, and scrape the cylinder walls on the downward stroke, so as to prevent lubricating oil entering the combustion space. One of these rings may be located just below the compression rings and the other in the piston skirt.

DEVELOPMENT

The first internal combustion engine to use an injection system in which the fuel oil was forced into the combustion space under pressure from a pump, was constructed in 1890 in accordance with the patents of the English invent...