So I've heard about railroads "re-gearing" their locomotives' traction motors. How does this work? What is the purpose of doing this?
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GenesisFan99 posted:So I've heard about railroads "re-gearing" their locomotives' traction motors. How does this work? What is the purpose of doing this?
For example, a standard freight unit (GP9, GP40, SD40-2, etc., etc., etc.) have a gear ratio of 62:15, i.e. 62 teeth on the axle bull gear, and 15 teeth on the traction motor pinion drive gear. Such a "gear ratio" keeps the armature at a safe RPM at train speeds up to 70 MPH.
Another example would be a passenger unit (GP9, GP40, SD40-2, SDP40F, F40PH, etc.) having a gear ratio of 60:17, i.e. 60 teeth on the axle bull gear, and 17 teeth on the traction motor pinion drive gear. Such a gear ratio would allow speeds up to about 102 MPH, and still a safe RPM speed for the traction motor armature.
The above information is applicable to "older" units with DC traction motors, and does NOT apply to the very modern AC traction freight or passenger units.
Hot Water - Do you have any data on locomotive gearing vs tractive effort? I assume tractive effort would be reduced for the higher speed gearing vs lower speed gearing.
Matt A posted:Hot Water - Do you have any data on locomotive gearing vs tractive effort?
No, you might have to try Google for such information.
I assume tractive effort would be reduced for the higher speed gearing vs lower speed gearing.
Not necessarily. The big concern with ANY of the various gear ratios is, minimum continuous speed, which means that a freight geared locomotive can operate "continuously" at say 10 MPH, without overheat damage to the traction motors. However, the minimum continuous speed of a passenger geared unit, might be as high as, say 20 MPH, thus passenger assigned units MUST be kept at higher speeds on mountain grades.
The gearing between a traction motor and an axle serves two purposes. First, it reduces the rotational speed (RPM) of the axle (and its gear) compared to the rotational speed of the motor. In the example given by HW, 62 teeth and 15 teeth produces a gear ratio of 62/15 = 4.13. So, the motor is rotating 4.13 times faster than the axle. The faster the motor rotates, the more power it develops, and the more power available to propel the locomotive. Second, the gearing multiplies the torque delivered to the axle by the motor, in this case by a factor of 4.13, which similarly multiplies the tractive effort (thrust force) produced by the wheels compared to 1:1 gearing. In the real world, the motor torque, size (diameter and length), maximum RPM, wheel diameter, maximum road speed and gear ratio are selected as necessary to obtain the required locomotive performance.
MELGAR
MELGAR posted:The gearing between a traction motor and an axle serves two purposes. First, it reduces the rotational speed (RPM) of the axle (and its gear) compared to the rotational speed of the motor. In the example given by HW, 62 teeth and 15 teeth produces a gear ratio of 62/15 = 4.13. So, the motor is rotating 4.13 times faster than the axle. The faster the motor rotates, the more power it develops, and the more power available to propel the locomotive.
Well, THAT all depends on the voltage applied to the DC series wound traction motors. Just because the RPM increases does NOT mean that the horse power increases, without subsequent increasing voltage from the main generator.
Second, the gearing multiplies the torque delivered to the axle by the motor, in this case by a factor of 4.13, which similarly multiplies the tractive effort (thrust force) produced by the wheels compared to 1:1 gearing. In the real world, the motor torque, size (diameter and length), maximum RPM, wheel diameter, maximum road speed and gear ratio are selected as necessary to obtain the required locomotive performance.
MELGAR
Hot Water posted:MELGAR posted:The gearing between a traction motor and an axle serves two purposes. First, it reduces the rotational speed (RPM) of the axle (and its gear) compared to the rotational speed of the motor. In the example given by HW, 62 teeth and 15 teeth produces a gear ratio of 62/15 = 4.13. So, the motor is rotating 4.13 times faster than the axle. The faster the motor rotates, the more power it develops, and the more power available to propel the locomotive.
Well, THAT all depends on the voltage applied to the DC series wound traction motors. Just because the RPM increases does NOT mean that the horse power increases, without subsequent increasing voltage from the main generator.
Second, the gearing multiplies the torque delivered to the axle by the motor, in this case by a factor of 4.13, which similarly multiplies the tractive effort (thrust force) produced by the wheels compared to 1:1 gearing. In the real world, the motor torque, size (diameter and length), maximum RPM, wheel diameter, maximum road speed and gear ratio are selected as necessary to obtain the required locomotive performance.
MELGAR
Of course, it does. But the variables I mentioned are generally determined by looking at the motor torque available at stall ( zero RPM) and the motor power at maximum RPM, both of which depend on the electrical characteristics of the motor and the generator (alternator).
MELGAR
Found my answer half way down the page.
Hot Water posted:Well, THAT all depends on the voltage applied to the DC series wound traction motors. Just because the RPM increases does NOT mean that the horse power increases, without subsequent increasing voltage from the main generator.
Forgive my ignorance, but how is the speed of a DC traction motor controlled? Is it as simple as more voltage = more speed, or are other factors involved? I believe that AC traction motor speed is controlled by adjusting the frequency of the electric current, if I'm correct.
Tom
Is there such thing as a "dual-service" gear ratio balancing higher speed with good tractive effort?
GenesisFan99 posted:Is there such thing as a "dual-service" gear ratio balancing higher speed with good tractive effort?
No.
