Please some one help me to understand this.
When an engineer Notches on his throttle from the lead locomotive,How do the other Locomotives respond with the lead Unit?
I know that each Locomotive has MU Hoses connected to each Unit,Are those MU Cable"s responceable for the Unit to Unit Motion responce?
In other words,How do lets say (3) Units work as one Unit?
Thanks.
There are lots of separate wires inside the MU cables, which control various standardized functions as well as determining which locomotive controls the others. Randy Stahl will give you not only a detailed listing of what each wire does, but can also tell you which wires are given different connections on different railroads… and as a result, which locomotives aren’t happy running with others, and what to do about it.
Note that the “run” system that produces ‘throttle notches’ (the ‘idle’ and ‘run’ positions up to eight) are part of the control system that EMD designed to make MU control practical for the control systems (relay logic!) of the '30s and '40s. There are more modern systems that give better control of trailing-unit power: one of the very earliest implementations of radio control, IIRC, used proportional gauges on the unit’s front and rear drawbars to control the power developed by the locomotive in step with train resistance rather than leading-unit throttle position (which is NOT the best thing to use for midtrain helpers in many cases!) Current systems of DPU (for example the system used to control the ‘trailing’ locomotive on some coal trains) give nearly continuous control over the diesel engine and traction-alternator settings – you can hear the engine lazily rev up and down in very small increments with load changes. These are not classic “MU” systems, of course, and depend on developments in electronics that came along much later, and specialized equipment not necessarily common to all locomotives. Again, Randy Stahl can give you detailed and specific knowledge about these things.
Of course distributed power uses radio to send signals to the mid-train and/or end of train helpers.
Randy hasn’t answered, he can probably give a better answer than me, but I can help a little anyway.
The governor controlling a locomotive’s engine is a hydraulic type governor that uses engine lubricating oil as a medium. Engines of this size typically have hydraulic governors because of the effort needed to move the fuel control mechanism.
A basic description of how the governor works is a set of flywheights act against a spring to position a pilot valve that controls the position of a servo piston.
Also in the governor are five solenoids controlled by the throttle position 1 through 8. One solenoid is a run/stop, the other four are for runs 1-8. Each of these solenoids are trainlined and work simultaneously with the other governors’s solenoids.
I know how hydraulic governors work from my own experience, but my own experience does not include locomotive engines. The solenoids I have learned about here in the forum. What I do not know is if the solenoids act to modify hydraulic pressure, or if they mechanicaly act to limit fuel rack movement.
Another problem is transitioning from series to parrellel operation of the traction motors. which is something that each locomotive does individually, but must be done equally.
In new engines, electronic unit injectors have electronically controlled spill valves. A unit injector is an injector that performs metering, timing, and delivery funtions all in a single unit. The spill valve provides hydraulic lock when closed and the injector is delivering the fuel charge. When the valve opens, pressure is no longer contained within the injector even though the pumping action of the plunger continues by way of the cam and rocker. Because of this, a physical governor is not present on a computer controlled engine, and different “runs” are simulated by changing “maps” to control injector timing and metering.
Baldwin Locomotives had MU hoses[:p], with that pneumatic MU equipment. IIRC, the hoses on the pilots on a locomotive with electrical MU equipment are for the sanders, train line and Loco/Independant brakes.
The 8 engine “notches” are created by actuating 4 solenoids (labled A, B, C and D) in the engine governor. Three of them act on a triangular plate of a geometry such that they will increment engine speed as follows:
A = 1
B = 4
C = 2
D= -2
By actuating in combinations, you get 8 unique settings
idle = none
N1 = none
N2 = A
N3 = C
N4 = A + C
N5 = B + C + D
N6 = A + B + C + D
N7 = B + C
N9 = A + B + C
Theoretically, you only need 3 solenoids to get 8 unique settings. The D solenoid is the shut down solenoid and it’s energized in notches 5 and 6 to give it some exercise to keep it from sticking.
The D solenoid is also used in low idle in combination with A.
The MU jumper on locomotives has 27 pins. Each of the circuits is isolated from the rest of the locomotive by trainline relays so that a problem on one locomotive can’t cause problems on the rest. 4 of the train line wires are used for the throttle swithces. The rest are used for other control funcitions like generator field on/off, reverser position (this one is criss-crossed from front to rear so that all locomotive will move in the right direction!), dynamic brk control, sanding, headlight on/off - bright/dim - front/rear, - there is an AAR std for which pins control what. Additionally, there are some spares so the individual railroads can do custom things such as Conrail using Harmon Select-a-Power.
Somewhere in the posts is a list of all the pinouts for the 27 pin MU head. Each of the 27 pins controls a specific locomotive function. Everyone who has answered so far is right on, and a good understanding of MU locomotive function is apparent. I’ll use an example pinout to help us understand : pin 8 & pin 9., forward & reverse. When tyhe engineer moves the reverser into forward , wire # 8T becomes energized, not only does this wire run throw the switches in the lead locomotive but pin 8 also becomes live in the MU head causing all the locomotives to follow. I’ll try to head off possible confusion by saying that if you have a consist of locomotives with one or more facing the opposite direction, you don’t want them all going “forward”, some locomotives must go in reverse in the consist. Wires 8&9 T simply switch pinouts on the front and rear of the engine.
The Westinghouse air throttle system that was referred to had no advantage and many limitations. (they are kinda neat though)
Randy
ps I just returned from a road job… still not myself
In other words It’s like the lead unit giving comands to the other units through the MU cables.
The thing I find most interesting is the fact that the MU system as we know it today was invented in 1904 by Frank Sprague for his trolley cars. If I remember correctly the cars used on the North Shore Line had 9 pins. I also recall some early diesel locomotives having less than 27 pins .
The AAR specified pinouts sure are handy… The problems are when a RR decides to use the spare pins for stuff like MU ground relay reset, the RR down the street decides that they will use the same pin for a lighting negative !!!
Randy
I just remembered the thread that contains the pinout listings… Smoke sparks fire & scary noises !!!
Randy
I don’t know anything about MU pinouts but just watching MU’ed units switching - they pretty much all belch smoke at the same time so the reaction times must be very close.
dd