Locomotive Gearbox

[Demeter Exekutor]

Thisgearing is part of the machinery within the locomotive and should not be confused with the pinion that propels a rack locomotive along the rack between the rails. The geared steam locomotives that have been built have been for conventional track, relying on the adhesion between wheels and rail.

The steam locomotive, as commonly employed, has its pistons directly attached to cranks on the driving wheels; thus, there is no gearing, one revolution of the driving wheels is equivalent to one revolution of the crank and thus two power strokes per piston (steam locomotives are almost universally double-acting, unlike the more familiar internal combustion engine).

The maximum rotational speed is fairly fixed for a given engine technology. Given the lack of any variable-ratio transmission between the piston engine and the wheels, the designer is forced to compromise between desired torque and desired maximum speed; the radius of the driving wheels determines this. The radius of the crank affixed to the wheel is of course less than this; its radius determines the length of the piston stroke. This cannot be too large, for the locomotive will be unable to generate enough steam to supply those large cylinders at speed; it cannot be too small, or the available starting torque and thus tractive effort will be too small, and the locomotive will not be able to start a train.

Many industrial applications require a low speed locomotive with ample starting tractive effort. These industries range from mining and quarry operations to forestry and logging operations. Steeply graded lines, especially when the track is cheaply built and not suited to high speeds, will also favour the usage of a locomotive with a high tractive effort. Although the trade-off of speed versus torque can be adjusted in favour of torque and tractive effort by reducing the size of the driving wheels, there is a practical limit below which this cannot be done without making the piston stroke too short on a directly-driven locomotive.

The solution is to separate the crank from the wheels, firstly allowing for a reasonable piston stroke and crank radius without requiring larger than desired driving wheels, and secondly allowing for reduction in rotational speed via gearing. Such a locomotive is a geared locomotive. Most were and are still single speed, but some did employ a variable-ratio gearbox and multiple ratios.

The vast majority of geared locomotives in the world were built to one of three distinct designs, whether licensed and official, or clones built after the expiration of key patents. Of the types, the Shay locomotive was the most numerous and best known. The overwhelming majority operated on the North American region, but with a number in use in various parts of South America and a fair number in Australia and New Zealand, including home-developed types.

These were not the first locomotives to use geared transmission. Richard Trevithick's Coalbrookdale Locomotive used a large gear instead of side rods to link the crankshaft to the driving axles, with a net 1:1 gear ratio. The early Grasshopper (1832), Crab (1837) and Mud Digger (1842) locomotives built for the Baltimore and Ohio Railroad used gear ratios on the order of 2:1 so that each turn of the crankshaft caused about two turns of the driving axles. This allowed use of relatively small driving wheels without sacrificing speed.[1]

The Shay locomotive features an offset boiler with a multiple-cylinder engine affixed to it on the opposite side, driving a longitudinal shaft geared to the axles via bevel gears (see also Ephraim Shay, inventor).

Classes B and C Climax locomotives have two inclined cylinders driving a transverse crankshaft, geared to a longitudinal driveshaft placed centrally on the locomotive and driving the powered trucks via internal gearing.

Some geared steam locomotives are still at work in the sugar plantations of Indonesia, and no doubt elsewhere too[citation needed], but in most countries they may now be seen only on tourist lines, preservation sites and museums. The particular advantage in cane sugar operations is the ability to use the dried solid residue of pressing the cane (see bagasse) as a fuel of trivial cost, providing that low cost technical labor is available to maintain the locomotives.

Wide variety of types still in use at sugar mills. Most are long wheelbase 0-10-0 locomotives that use an articulation technique incorporating a geared drive to the outer-most axles, the inner pair being direct-drive.

The Alishan Forest Railway in Taiwan operated 22 Shay locomotives in the past, with the oldest dating to 1910 Archived 2016-04-17 at the Wayback Machine. Sixteen of the original 22 have been preserved, with 3 in operational condition and 1 preserved on the Puffing Billy Railway.

I'd like to add shims on each side of the gear box axle to minimize the rocking so that the locomotive runs more smoothly. If I press down on top of the gear tower to keep it from rocking, there is a noticeable difference in smoothness.

I fixed a loco for a friend with the same problem...the gearbox was flopping around from side-to-side, but all it took to remedy it was a couple sheets of fairly thick styrene with some thinner sheet styrene cemented to it to create a tight fit within the loco's frame.

Thanks, Ed, and funny you should mention the above. I was looking through that very clinic .pdf a few days ago (on another project) and remember seeing the torque arm remedy. Whoda thunk I might be using it soon after on another project only because I decided to organize my locomotive & rolling stock product boxes that I had stacked in the closet.

The photo on pg. 26 shows the one end of the torqure arm attached to the top of the motor. I think I'll opt to bend it 90o at that location and affix it to the front of the motor bracket. I'd rather do that than risk drilling a hole into the top of the can motor housing.

I noticed that the original black tubing was slipping on the motor shaft when the motor stalled so I replaced it with DuBro silicone fuel line, which I've successfully used on a few other locomotive rehabs:

Not only has this eliminated the tubing slippage on the motor shaft, the axial rocking has diminished noticeably, as well - although not completely. The torque arm will still be needed - especially if I want to get improved slow-speed from the locomotive.

Looking at this, you might use JB-Weld or epoxy on the front of the motor and back of the gearbox and make a turnbuckle arrangement with threaded rod to go between them. This would let you fine-adjust the alignment and then put a little Loctite to hold it there.

It may be the angle of the photo but it appears that the motor and gearbox shafts are on a different level. I have found that same situation on 90 percent of my brass too. And when the driver springs compress it will be even greater.

I have fixed this several ways. Slot the holes in the motor mount. Shim under the motor mount. And slant the gearbox rearward and tilt the motor shaft/mount to line up. I also line up the shafts with the springs fully compressed. I always add as much weight to the locomotive so the springs are fully compressed anyway.

Another way to fix the gearbox wobble side to side is to file the bottom of the housing and maybe a little off the lower cover. Careful not to take too much off. The mesh of the idler gear and axle gear will be too deep.

As a major supplier of locomotive traction gearing for freight and commuter rail applications, GearWorld (GW) manufactures a full range of aftermarket gearing for Original Equipment Manufacturer (OEM) AC and DC locomotives worldwide.

I had been doing some reading about British Railways No 10100 which is better known as the Fell Locomotive. This was a prototype 2-D-2 locomotive that was perhaps the oddest (and oddest looking) loco to have graced the UK rail network and was an attempt to build a 2000hp mainline diesel engine using a mechanical transmission.

The transmission was brilliantly conceived and it is clear how it would suit the needs of mainline operation. But then I had a Eureka moment and realised that this might work well in a LEGO loco too. Well, not the whole four engines and three differentials thing, but with two motors and a single differential it might be possible to increase the controllable range of speeds achievable.

The H10-44 has a slightly longer geartrain due to the need to power both bogies. This loco use a pair of M-motors placed at either end of the differential. The model was built with the option to alter the final ratio by sliding the relevant sized gears along the driveshaft to engage with the differential, with either 1:1 gearing for some proper slow speed switching capability or 1:3 for higher speed running.

The first thing to do was to work out how the motors would work with each other in order to drive the model as I intended. Using a spreadsheet I was able to come up with a motor map that looked reasonable. The graph below shows it in graphic form.

Button 1 increases power/moves the model forward, button 2 decreases power/moves the model backwards and button 0 is the emergency stop. Dial 3 in the centre is the train speed while dials 4 and 5 show the motor speed for each motor.

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