I’ve been designing and selling industrial power transmission equipment for 3+ decades.
Industrial applications are “purer” in the sense we don’t deal with automatic transmissions, differentials, A/C compressors, power steering, ECUs, sensors, vacuum leaks, and all the other crap associated with today’s automobiles, but the basic energy principles are the same.
I’ll try to put this in a way that everyone gets…
Horsepower and torque are like weird cousins… they can’t exist without each other, but they really aren’t the same, and the balance of each can vary greatly in any situation.
I’ll give a few basic examples in extreme to try to help everyone understand what I’m getting at…
Example of torque:
Theoretically, if you take a 1hp/1750rpm electric motor and mount it on a table and turn it on, it produces 1HP and spins at 1750rpm. A strong guy with good gloves could probably stop the 5/8” diameter spinning shaft with his hands, since the motor itself produces very little torque.
Now take this same 1hp/1750rpm motor and connect it to a 50 to 1 reduction gearbox.
The first thing you will notice is now the output shaft of the gearbox is probably about 1 1/2” in diameter. If you could measure the power at this shaft you would probably now have something like 3/4hp (loss due to drive inefficiencies/friction) and the shaft would be turning at only 35rpm.
(Piece of cake to stop this, right? …. Wrong! If you attempted to stop this shaft with your hand you would wind up in a bloody ball in the corner of the room.)
While the output HP has actually been reduced, the output torque is now many times the input torque.
Another example of torque due to gear reduction is your basic electric drill. Very little input torque, but gobs of output torque.
Example of HP:
Today’s modern Formula 1 race cars produce roughly 800hp from a rather small 2.4L V8. To produce this HP, the engine runs at very high rpm….idles at 4000rpm and is governed to a max of 19,000rpm. This engine produces tons of HP at these high rpms, but very little torque due to it’s very high rpm powerband and limited displacement. When racing on a hilly track, the main thing that gets it up the hill is momentum, and the HP keeps this momentum going as long as the car is moving at a good rate of speed.
Now if you could theoretically use this same 800hp F1 car and try to tow your TM from a standing start up the same hilly track, you will find you won’t get very far due to the very limited torque of the engine, along with the high gearing of the tranny. (Not the ideal towing package!)
So in summary, you can have lots of torque with very little HP, as well as have lots of HP with very little torque. You can’t have one without the other, but the amounts of each can vary greatly, depending on the application.
Basic “rule of thumb” engine principles:
Smaller, faster rpm gas engines produce very little torque.
Larger, slower rpm gas engines produce lots of torque.
Diesel engines produce even more torque at almost any displacement, and at lower rpm than gas.
(Diesel engines will usually produce less HP at a given displacement than a gas engine, but with much more torque.)
So with some basic understanding of the above, you could then theorize that if you could take the same load and course (lets use the E350 towing a TM, going from NOLA to HTX, and use cruise control to maintain speed (no human variable input)) but have three different setups… the first would be the v6, then the v8, then the v8 diesel. Basically the only thing different is the engines, which of course all offer different HP and torque numbers.
We'll say they all weigh 8000 lbs and the cruise is set to 65mph.
The v6 will struggle the most trying to stay in the powerband and produce the HP and torque required to go up the hills with the load and maintain the set speed.
(The slower the vehicle is moving, the more torque required to get it moving.)
(The faster the vehicle is moving, the more HP is required to keep it moving.)
The v8 will struggle less due to the additional torque and HP.
The v8 diesel will struggle even less due to its tremendous torque at the lower rpm ranges.
I doubt that the engine/tranny would even react to the hills/overpasses.
In simplest terms, torque is what starts your vehicle moving, or headed up hill, or accelerating, while HP is what maintains this once moving, but they both must be present in certain degrees in both instances.
Now getting back to the overdrive issue…
To successfully use OD while towing, you need to be very conscious of many variables.
First, you would need enough HP to maintain speed of your rig without the need to downshift to increase torque to climb hills/overpasses. Most smaller vehicles (v6’s) would lack this ability since they lack HP/torque, and a downshift would be required to produce more HP/torque to maintain speed up the hill. The downshift would actually produce more HP from the engine as well since the engine would move into the “sweet spot” in its powerband. This constant changing is what you want to avoid.
This means you would need to find that correct highway speed for your load and your TV to produce enough balance of HP to lock the converter without it needing to kick in and out. While I may agree that today’s TVs with larger v8’s and for sure diesels, would have this ability under good circumstances, the v6 would certainly not.
|