I keep reading about the throttle on diesel engines bring set to a particular notch. Is each notch a set speed? I always thought that the throttle would move smoothly and could be set at any place for any desired speed. What is it with notches please? [:)]
“Back in the day” traction control was via relays and resistance coils (including electric locomotives). Eight notches allowed reasonable control throughout the range of zero to everything. The concept also allowed MUing locomotives as only a few wires, energized in various combinations, could control the unmanned locomotives through the notches.
How fast the locomotive goes in each notch is dependent of what it’s pulling. Notch 8 with a “full load” on the drawbar might only get you a few miles per hour. One account I read involving AC locomotives had them at less than 1 mph with several engines in notch 8, a substantial number of loaded coal hoppers behind them, and an upgrade.
A previous discussion (you could do a search of the forum) brought out that with the sophisticated electronics available today, the notches still exist, but throttles are a lot closer to being infinitely variable than they are to being restricted to the eight notches.
Notches on diesel-electric locomotives equate to Prime Mover RPM. Diesel Prime Movers normally operate at 1100 RPM or less at Full Throttle. Each manufacturer’s Prime Movers have different RPM settings for each notch.
AC diesel-electrics can pull at Run 8 (Wide open Throttle) at speeds of less than 1 MPH to the normal maximum of 70 MPH. DC diesel-electrics are bound by short time ratings on the DC traction motors…DC locomotives have ‘minimum continuous speeds’ that apply to the traction motors and depending on gearing and manufacturer the minimum continuous speed can range from 9 MPH to 14 MPH in freight locomotives and on passenger locomotives it was as high as 24 MPH.
Minimum continuous speed is that at which the traction motors can operate at full electrical load without overheating. At speeds less than minimum continuous speed, the traction motors will overheat…thus the 'short time ratings’s.
The reason there are 8 notches as opposed to 9 or 10 is that is the number of combinations you can get from a combination of three on/off switches.
The diesel engine governors have 3 solenoids that are either turned on or off. The various combinations give 8 distinct engine speeds (and corresponding loads)
Theoretically, you could add another solenoid and get 16 distinct settings, but that would be overkill. Eight gives enough HP regulation.
Didn’t some GEs have 16 notches
Domestic GE’s, starting with the U25B, did indeed have 16 notches. When they were MU’ed behind EMD’s or Alcos, every other notch was skipped when the throttle was opened or moved on the lead unit.
Baldwins originally had an air throttle which allowed infinitely many variations on power but also restricted them to operating in multiple only with their own kind. Air throttles also did not respond well in multiple beyond the fourth unit.
The PCC streetcar, you know, the one which kind of looks like a 40’s vintage bus, was supposed to have a controller with a large number of notches. The PCC (Presidential Conference Car after a “sitdown” of heads of streetcal companies) was supposed to bring streetcars into the modern era and save the industry. It had the bus-like carbody, insider roller bearing trucks. The traction motors were not “nose hung” like on a Diesel loco and every other interurban and streetcar before it – instead, the motors were “fully suspended” on the truck frame, had an automotive-style drive shaft with a double cardan joint leading to a 90-degree gear box on the axle (not a “differential” as it still had a conventional railroad solid axle). It also had an electromagnetic brake that directly contacted the track instead of acting on the wheels – the thing could accelerate like a Porsche and stop on a dime (or at least compared to other railroad tech).
If there are any PCC cars left (like on that SF Market Street line), I guess they are regarded as old and frumpy, but in their day, the PCC cars were revolutionary. They still are a new thing in this day – the Budd Pioneer III ultra-lightweight 4-axle coach introduced the inside roller bearing truck to the heavy rail world. and I believe the Silverliners had the PCC-style traction motor drivelines. Amfleet coaches have PCC-style running gear.
My mother told me about the Chicago CTA “new streetcars” (PCC cars) back in the day and about how fast those things ran. My understanding is that the CTA elevated trains were based on PCC running gear – inside bearing truck, right-angle traction motor driveline, track brake and all. They were wider than a streetcar, but they were narrower at platform level and then kind of bulged outward to give more room – the North Shore Electroliner had the same kind of bulge to operate on the El tracks.
Anyway, there is a point to this story. The PCC controller was supposed to be this high tech (pre-electron
The Cineston controller used on PCC cars had a total of 8 notches, 3 notches of acceleration, coasting, 3 notches of braking, and off. The notches controlled the motors by a rate of acceleration or deceleration (braking) rather than to a specific speed. This is what provided the improved performance in traffic which was alluded to in other postings.
CTA Rapid Transit cars 6201-6720 and 1-50 were built using a variety of parts salvaged from trade-in postwar PCC streetcars. Salvaged parts included trucks, window fittings and other odds and ends. The bulge above floor level continues to this day with current CTA rapid transit equipment.
Most NON-MUable switchers had a smooth acting Notch-less throttle
The Cineston controller was not used on PCC streetcars but was used on many rapid transit cars. The important point about the PCC control, and this applies to both Westinghouse and GE electrical setups, in both Pullman and St. Louis cars, and also applies to the Tatra Czeckoslovakian and La Brugious European cars (outsold USA by about 5 times!) is that a particular depression of the foot pedal, which operates a reostat, or on Chicago hand control cars a particular movement of the acceleration handle or throttle, does not pick a particular setting of the 50 or so resistance steps in the motor electrical power supply. Instead, it determines how fast a pilot motor moves from the highest resistance step to zero resistance through all 50 steps. The idea was that the foot pedal would control the rate of acceleration but not the balancing speed. Just a slight depression of the pedal would allow gradual acceleration but still get the car to top speed. Putting the foot to the floor would give you maximum accleration, and on level ground that would be about four miles per hour per second. So in about ten seconds you would be close to maximum speed of 40mph. The idea was a car that could keep up in auto traffic in all conditions. Braking was similarly rapid with dynamic braking, the resistance grids used for winter heating and the air flow reversed in the summer, a mechanical or air parking brake, and magnetic track brakes that could slow the car even when leaves or ice on the rail would otherwise make for slide conditions. The best operators would not use maximum acceleration except when required and would feather their feet movement, depressing the pedal slightly and the more as the car accelerated. Similarly, most systems discouraged use of maximum braking, or even anything above normal service braking not using the magnetic track brakes, except again when required. PCC’s are still considered a good serviceable transit vehicle some 70 years after introduction and are running in regular service in the U
Don’t forget McKinney Avenue Transit Authority in Dallas. MATA has 2 PCCs from Philadelphia that have been regauged to 4’ 8.5" from Philadelphia’s wider gauge. The cars currently are in storage at DART’s S&I facility ar Fair Park awaiting the second reversing loop to be completed as the PCCs do not back up worth a darn.
Well, sort of. They had “half notches”. There were still 8 distinct engine speeds governed by three solenoids in the governor, but you could move the controller a “half notch” that would get you the next notch’s engine speed without adding any load. It gave the engineer a way to avoid some of the turbo lag.
Most of the 1/2 notch junk was ripped out of the U25s in latter years, however.
PCC footnote. GE sold the “T” in 1952 on an experimental less expensive cam controller for the 50 “picture windows” Pullman PCC’s instead of the pilot motor control described earlier. These were good cars except for this feature which many people tell me was a mistake. The older “wartime” 1945 cars are what serve the Mattapan - Ashmont line. Restored to original color scheme! And a scenic fast ride.