A number of electric railways around the world use locomotives of the Bo-Bo-Bo ("Tri-Bo") configuration, in which three two-axle trucks are used (the middle truck has a certain amount of side play). The tri-bo arrangement is used because it produces less track wear than the equivalent locomotive using 2 x three-axle trucks.
On many rail networks the loading gauge prevents the tri-bo arrangement being used for diesels but in the U.S. this would be less of a problem. Has there ever been an experimental tri-bo diesel, or has one ever been proposed?
The only one of which I'm aware was EMD's GM10B demonstrator, which was a 10,000 HP B-B-B locomotive which demonstrated on Conrail prior to 1982.
One of the 'big deals' on Class 1 main line engines is fuel capacity. Currently most engines being produced have a fuel capacity of between 4000 & 5000 US gallons. The carriers have built the plant that they have retained in operation to be able to handle the C-C wheel arrangements of todays 6 axle locomotives and the lines that can't handle todays road power have either been abandoned or sold to Short Line operators. Having the Tri-Bo configuration would reduce the fuel capacity.
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The best known TriBo locomotives are the New Zealand Railways DJ class:
https://en.wikipedia.org/wiki/New_Zealand_DJ_class_locomotive
In a larger USA locomotive fuel tanks might be placed between the trucks, but an additional tank in the hood would probably be required.
The DJ has an unusual ride compared to a locomotive with two trucks, particularly entering a curve when the direction changes in stages as the trucks enter the curve.
Peter
I wonder if the steering ability of trucks now cancels the Tri-Bo advantage?
The Channel Tunnel Class 9 locomotives are a notable example of the Bo-Bo-Bo wheel arrangement:
https://en.wikipedia.org/wiki/Eurotunnel_Class_9
The wheel arrangement is also used on several classes of electric locomotive in Japan.
Another notable example is the Swiss RE620,which was at one time the most powerful electric locomotive in the world:
https://en.wikipedia.org/wiki/SBB-CFF-FFS_Re_620
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carnej1 The Channel Tunnel Class 9 locomotives are a notable example of the Bo-Bo-Bo wheel arrangement: https://en.wikipedia.org/wiki/Eurotunnel_Class_9 The wheel arrangement is also used on several classes of electric locomotive in Japan. Another notable example is the Swiss RE620,which was at one time the most powerful electric locomotive in the world: https://en.wikipedia.org/wiki/SBB-CFF-FFS_Re_620
Of course fuel tank space is not an issue on electric locomotives.
In 1951 Westinghouse built a couple of pairs of expermental ignitron rectifier electric locos for PRR. One pair (E3b) was B-B-B, and the other pair (E3c) was C-C.
Buslist carnej1 The Channel Tunnel Class 9 locomotives are a notable example of the Bo-Bo-Bo wheel arrangement: https://en.wikipedia.org/wiki/Eurotunnel_Class_9 The wheel arrangement is also used on several classes of electric locomotive in Japan. Another notable example is the Swiss RE620,which was at one time the most powerful electric locomotive in the world: https://en.wikipedia.org/wiki/SBB-CFF-FFS_Re_620 Of course fuel tank space is not an issue on electric locomotives.
Of course it isn't but to me the interesting question is why is the wheel arrangement semi-common in electric traction?
I can think of a few possible answers;
1. On locomotives such as the GM-10 demonstrator and the Swiss class mentioned above,could the arrangement of the trucks allow for the use of larger traction motors than conventional three axle C trucks would?
2. Is there an advantage to the triple B arrangement in higher speed service compared to a CC design?
3. Does a Tri Bo locomotive perform better on lines with tighter curve radiuses, esp at speed?
Getting back to Buslist's point about Diesel electrics I can't see any advantage to a Tri-Bo design over six axle locomotives and considerable drawbacks. the New Zealand diesels referenced were designed for operating on extremely light rail branch lines. In North America early in the age of dieselization there were a number of light roadswitcher designs that used A-1-A trucks for similiar applications....
carnej1 Of course it isn't but to me the interesting question is why is the wheel arrangement semi-common in electric traction? I can think of a few possible answers; 1. On locomotives such as the GM-10 demonstrator and the Swiss class mentioned above,could the arrangement of the trucks allow for the use of larger traction motors than conventional three axle C trucks would?
My undersanding was that the GM10B was 1.5 AEM-7's with a different gear ratio for the motors. IIRC, the motors were truck mounted, which brings question about how a three axle truck could be made to work. My recollection is that the GM10B also used 50 inch doameter wheels, which would imply a larger motor as one would expect from 1,600 HP per axle with a DC motor.
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