I’ve heaard somewhere, I think it was an article in Model Railroader,that some locomotives now come with steerable trucks. What good does this do, does it let trains go off track or something[:D]. What good does steering trucks do?
Simpy speaking it reduces wear/friction out not only in curves, but also in the locomotive truck itself saving in maintance costs of both.
they are designed so that bigger 6 axle power can go where 4 axle power could only go befor due to tight curves…
csx engineer
While on topic here…
It looks like Amtrak’s Genesis has steerable trucks. I’ve looked at pics of the trucks and they look… steerable. It may be only four axle, but it is very long, so I’m guessing it helps. Can anyone confirm this?
In the world of physics, a train operates most effieciently on a straight piece of track and when the axles are perpendicular to the rails (wheels would be parallel). When a locomotive traverses a curve with non-steerable wheels, the wheels and axles are no longer perpendicular to the rails, which results in a loss of effiencey. The steerable trucks alters the truck such that the the axles will be perpendicular to the rails (and center point of the curve) in a curve.
Things often get named inappropriately. In this case ‘self-aligning’ might have been better than ‘steerable’.
Depends upon whether or not the self-steering is passive or forced. The EMD HTCR and HTCR II are passive, and self-aligning would be an accurate description. But the “B” truck used under the ABB-SLM “Lok 2000” locomotives is a forced steer design. The axles assume a radial position because the truck is rotated from being aligned straight with the locomotive body. Examples of the “Lok 2000” are the Swiss SBB Re 460 locomotives, and the Finnish Vr2 locomotives.
Is the “self aligning” part similar to the front truck on a 4-4-2 steam locomotive, in that the whole truck pivots on a center pin?
Good point, beaulieu. Perhaps ‘auto’ instead of ‘self’ might be more accurate. But IMHO ‘steerable’ implies human interaction which is definitely missing in both designs.
Art
Question, Do they have a steering wheel in the cab to steer the trucks, or do they steer themselves?[%-)]
No, it is not. When the locomotive on your 4-4-2 goes around a curve the truck rotates around the center pin, but the distance between the center of the front axle on the truck, and the rear axle of the truck is the same on both sides. If the front truck of the same locomotive was a radial steer truck then they would be different. Let’s say the locomotive was going around a curve to the left. The axles within the truck would shift to a radial position and point to the center of the curve. If you would measure the distance from the center of the front axle to the rear axle, the distance would be less on the left side of the truck, than it would be on the right side of the truck. Further more the distance of the left side would be less than the distance measured when the locomotive is on straight track and the right side would be greater than the measured distance on straight track.
Am I reading this correctly? In a turn to the left, for example, the wheelbase of the two left wheels becomes less than the wheelbase of the two right wheels?
No, the “steering” is the result of forces applied to the locomotive wheels by the track. They steer themselves, it is a function of the taper of the wheels. The wheels are smaller diameter on the outside and larger diameter near the flange. In a curve the locomotive wants to go straight because of Inertia, this pushes the outside wheel up the taper near the flange and lowers the inside wheel to near the outside smaller diameter. Since both wheels are locked together the outside wheel goes further for each revolution of the axle turning the locomotive into the direction of the curve and bringing things back into equilibrium. Ideally in a curve the axles will assume a radial position. In a normal truck they cannot so, so some wear results on both the wheel and rail because the wheel is not turning in exactly the direction its moving, there is a little slippage involved. The sharper the curve, and the longer the truck axle spacing the greater the force and wear. The “C” truck has a longer distance between the front and rear axles so it creates greater wear than a “B” truck. This is why in the US the only self-steering trucks are “C” trucks. The savings from wear on a “C” truck can offset the greater cost and complexity of the self-steering truck.
“B” truck is a two axle truck with both axles powered
“C” truck is a three axle truck with all three axles powered
wow thanks! One more question, B and C have all axels powered right, wha do you call an E unit axel where the middle axel is a dummy?
An E unit rode on two A1A trucks.
Yes, the wheelbase is slightly shorter on the left side during a left curve. It isn’t much, but it doesn’t take much.
Yes.
Ok, thanks. I understand the “what” part now. About the “how” part- Is there some sort of sensor, that somehow tells the wheelbase to shorten upon entering a curve?
No, it is a result of the wheel being moved by the curve of the rail, and a linkage rod diagonally connecting the two axles, so that when the left end of the front axle moves back the right end of the rear axle also moves back.
Is the linkage rod mechanism for a passive system, a forced system, or both?
For both, but there are additional linkages to the body or frame in a forced steer system.