The information provided by the "old engineer" is probably correct. The
E-5s and E-7s were equipped with 52:25 gear ratios which provided a top
speed of 117 mph. The E-8s and E-9s had 55:22 gear ratios which I
believe had a top speed around 102 mph. Traction motor armature speed
is the critical factor. By design, the armature speed (rate of
rotation) is limited to around 2200 to 2400 rpm. Above that speed,
mechanical rotational forces start causing the armature coils and
commutator bars to move outward and eventually fly apart. In addition,
the locomotive is also speed limited because it begins to run out of
power and additional electrical transition or shunting is not effective.
Locomotive gear ratios are always a compromise since they can't be
changed enroute like an automobile. On older locomotives with DC
generators. the transition and shunting of the electrical circuits
allowed the locomotive to accelerate, but the gear ratio is always the
final limiting factor. EMD offered gear ratios between 52:25 and 65:12.
The most common was 62:15. The number of teeth on the pinion and the
ring gear always adds up to 77 on EMD units. The high gear ratios
provided high speed while the lower gear ratios provided better
starting and load pulling capabilities at lower speeds. For instance,
and SD40-2 with a 62:15 gear ratio had its continuous tractive effort
at 11.2 mph. In other words, it could operate all day at that speed and
maximum tractive effort without overheating its traction motors. Below
that speed, the traction motors begin overheating and the locomotive is
now operating in its "short time" ratings. As the gear ratio is
increased, the continuous speed increases. A locomotive like an E-7,
might have its continuous speed around 20 mph. Thus, passenger diesel
locomotives did not work very well in freight service as the C&S proved
during the last days of the E-5s.
Thus, the Q assigned E-5s and E-7s to the TCZ because it was generally
lighter and, as I recall, its scheduled speed was higher. For the same
reason, the Q did not like to assign E-5s and E-7s to commuter service
once the E-8s and E-9s were on the property. Because the gear ratio was
lower on the later units, they could accelerate the commuter trains
better from each station stop. In the later years, you never saw an E-7
on a commuter train while they were very common on the through
passenger trains.
BTW, steam locomotives were similar. Their driving wheels were their
"gear ratio". Passenger locomotives such as an S-4 had larger driving
wheels (78 in.). They were capable of high speeds, but were not
particularly good with heavy freight loads. The M-4 2-10-4s, on the
other hand, had smaller drivers (64 in.). They were great with heavy
freight loads, but were not good at high speeds above say 60 or 65 mph.
Most 4-8-4s, like the O-5 were considered dual service locomotives and
had a compromise driver size (74 in. on the O-5). This allowed them to
have good heavy haul capabilities and reasonable passenger speeds.
Bill Barber
On Monday, January 27, 2003, at 04:55 AM, BRHSlist@yahoogroups.com
wrote:
Message: 6
Date: Sun, 26 Jan 2003 15:26:54 -0000
From: "baton580 <rplaehn@c...>"
<rplaehn@c...>
Subject: Twin Cities Engine Turnarounds
Does anyone know how the Q dispatched motive power on the passenger
trains to/from the Twin Cities? Particularly during the 50's and early
60's. I remember that the TCZ power tended to be E5 or E7 units with a
sprinkling of E8s or E9s thrown in, while the NCL and EB usually ran
with E8s or E9s. Was there any reason for this pattern of which type
of E, or just the random draw out of the pool in Chicago? An old Q
engineer once told me that the E5 and E7 units had higher speed
gearing and could make better time with the TCZ schedule and that the
8s and 9s had more hp for the longer EB and NCL consists. True, or
fiction?
I know that the TCZ power usually turned with the train at Mpls. and
returned on the next trip. Did units that went north on the NCL, EB
or Blackhawk wait in the twin cities and come back with the same train
or rotate first in, first out?
Finally, where did EB and NCL power lay over in St. Paul? Dayton's
Bluff or the small engine terminal on the east end of SPUD? I am
assuming (I know, never assume!) that the nb TCZ power layed overnight
in the Mpls. coachyard with the train, but what about the Blackhawk?
Same as the TCZ in Mpls?
Thanks in advance.
Bob Plaehn
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