Trains with multiple locomotives

When a train has more than one locomotive, is the acceleration and deceleration synchronized somehow?

It seems like it would be necessary, but I would think it would be pretty difficult to do manually.

Thanks for any information.

davidl wrote:When a train has more than one locomotive, is the acceleration and deceleration synchronized somehow?

It seems like it would be necessary, but I would think it would be pretty difficult to do manually.

Thanks for any information.

When units are MU'ed (multiple units) the lead locomotive is the controlling locomotive. What ever the engineer does, open/close the throttle, the other units follow suit. The giant cable that you see between the units is an electrical connection that makes this possible. The three small air-hoses, outside the brake-pipe, enables the lead locomotive to control air-brake functions for the consist.

When units are MU'ed (multiple units) the lead locomotive is the controlling locomotive. What ever the engineer does, open/close the throttle, the other units follow suit.

Does it work the same way for trains where the locomotives are facing different directions? I recently noticed some like that, and I was wondering if the "backwards" facing engines are running, or if they're just pulled by the "forward" facing engine.

Doesn't matter which way they face. The MU cables and air lines are universal. An engineer can give you the specifics on this: Before a multiple-unit consist leaves on a train the engineer will go through each unit and set it up for operation based on whether it is the lead locomotive or one of the trailing units.

Hope this helps!

jmp883 wrote:Doesn't matter which way they face. The MU cables and air lines are universal.

That answers my questions. Thanks!

If you watch a train with more than one unit, regardless of the way they are facing, when started they look somewhat as if they are surging. Even locomotives of the same manufacturer do this.

Different gearing, different engine types, different load ratings, different type, like a switch engine and a road engine, are all reasons they do this.

It is something train crews keep in mind as they are operating a train.

I works in reverse for braking a train as well.

The only thing that is really synchronised on the different locomotives is the throttle notches. Since all modern North American mainline locomotives have a standard 8 notch throttle schedule this is an easy task. By using 4 trainline wires in different combinations they get all 8 throttle notches and they all load just as if they were all controlled from their individual control stand. Forward and reverse use 2 more wires and the wiring of the locomotive and the m.u. jumper make sure the locomotive loads in the right direction regardless of the direction the locomotive is facing as compared to the leader. There is nothing the engineer needs to do to set this up. There is a switch that needs to be set on each locomotive but this is for the headlight circuits.
Now that AC units are common, a little caution is needed. You can hold stopped train on a grade using an AC locomotive in N-1 but that can damage the traction motors of a DC locomotive if it is also in the consist.

Although it is very rare, if a ground relay occurs in one of the units in a consist it may cause that unit to "fight" the others. (i.e. load westward when the rest of consist is loading eastward).

Synchronization of direction is achieved through a neat electrical design trick that has the direction wires crossed in an "X" within the locomotive and crossed again in another "X" within the jumper cable. Thus if a locomotive is in the lashup "backward" (cab to the rear) its direction feed from the jumper is applied on the opposite wire from the units that are in the lashup "forward". Consequently all the units move in the same direction (except if something is wrong, which happens occasionally).

With Woodward PG rail governors used on many EMD locomotives the factor limiting units that can be MU'ed and on line is usually around eight governors (not eight locomotives). When you have more than eight you start getting problems picking up the speed solenoids in the trailing units. This is one of the reasons that when the Erie Lackawanna ran E8 units in freight service about the largest E8 lashup you would see is four of these locomotives (each with two engines = eight governors).

When there are units from different manufacturers in the same consist, there can be a noticable difference in the time it takes to load-up. This was particularly true when you had a lash-up of EMD-GE-Alco units.

What about push/pull operation?

Same idea - each passenger car in a push pull train has the 27 pin Locomotive Control jumper, and therefore, each car can send the info back to the next one and so on and so on, until the Locomotive (if pushing, and the engineer operating from the cab car) gets the commands (pretty instantanous) that the engineer is doing in the cab car.