Curious about torque rise

[Big_Daddy_T]

Can you tell me what torque rise is? How to calculate it and its pratical application.

I was reading up on tractors and they specifically use torque rise as a selling point. So it must be important for towing. I do not presently grasp the idea of it yet.

 

[fox]

Basicly, on a tractor they pick a rated engine speed- say 2100. Then measure the torque and compare it to the max torque the egine makes. usually around 1500-1600.

You will find some thing like 11% to 25%.

Our Cummins has a rise and I think the other trucks have a FALL. That is why they have to downshift to pull up a hill.

 

[blacksheepdiesel]

On newer ag tractors the torque rise is more like 30 - 47%, mainly because of electronics being able to make the torque curve relatively flat over a broader rpm range.



Trent

 

[Big_Daddy_T]

If they can figure out percentages then there is a formula. Its not a very complicated formula. I saw it once and its 7th grade math. I need this formula to find the torque rise of the big 3s little diesels.



I came across this. "The MBE900 engine is targeted to promote your business success. High-torque rise at low rpm assures driveability. " So torque rise affects driveability. I wish to know why.

 

[Ray Torresdal]

torque rise

High torque rise just means that as the engine pulls down in rpm, the increased torque will let it pull as hard as at rated rpm. The result is less shifting. The ridiculous extreme was the first 237 hp. "Maxidyne" engines, coupled with a 5 speed. Having to listen to that engine groan at 12 or 1300 rpm all day was enough to make you contemplate jumping out the window into oncoming traffic! The other extreme was the early Detroits - you wanted as many gear choices as possible, because the couple hundred rpm you dropped shifting took you out of the engine's power band, unless you had the rpm turned up beyond factory. 2500 vs. 2100 was pretty standard.



Ray

 

[Big_Daddy_T]

"Torque rise, or torque reserve, is a measure of the lugging capability of an engine — the low-end power it can churn out when the going gets tough and the engine revs down — and the general rule of thumb is, the more torque rise, the better. When the engine sounds like it’s about to bog down and stall, and then it just keeps on going, like the Energizer rabbit, you can hear the torque reserve.



You can see torque reserve, too — mathematically. Look up peak torque and torque at rated horsepower on the engine spec sheet. Divide peak torque by torque at rated horsepower; carry it out to two decimal places — the answer will be 1 followed by a two-digit number. Knock off the 1 and that’s the torque rise. For example, 1. 27 would be 27 percent torque rise; a rating of 30 percent would be better — the higher the percentage, the more torque reserve the engine can deliver. That’s “lugging capacity. ”



This doesn’t matter much in your car. It matters more in your truck, especially if you go off-road or have to start off slow with a heavy tow load, like pulling a big boat out of the water.



But it matters a lot to construction equipment. Take an articulated wheel loader, for instance, challenged by extremely heavy loads at slow speeds and rough underfoot conditions. That’s no time to have the machine cough and wheeze. That’s why they put that beefy diesel in there; it has plenty of torque reserve. Diesel can run much higher BMEP and generate higher torque rise. (The British term for torque reserve is “backup,” which explains it pretty well. )"



Found that little snippet. Why do these light duty truck diesels not have any torque rise? The cummins actually has less than 1 percent torque rise. To have big torque rise significantly hampers hp output. So that must be why they removed it.

 

[baby.driver]

Notwithstanding what the sales brochure tells you I think you've got it backwards.

Torque is the ability to accelerate a load from a given speed to a higher speed.

If you could have 600 lb. ft. of torque at 2500rpm, and have that same 600 lb. ft. at 1600rpm, wouldn't you prefer that, rather than 425 at 2500 and 600 at 1600?

That is what is considered a flat torque curve. It means the same acceleration you experience from 40 to 50mph you can also get from 65 to 75mph.

Redbadge, I think you meant 3% to 4. 7% on a flat torque curve.

30 to 47% torque rise is nowhere near flat.

 

[DDahl]

High torque rise implies that the engine operates on a constant hp curve (or closer to it). HP is proportional to torque times RPM. This means that if your engine were operating on a constant hp curve, if max torque at 2500 rpm were 400 ft-lbs, max torque should be 800 ft-lbs at 1250 rpm (would we be so lucky). Shifting to a lower gear would be a total waste until the engine rpm fell below the speed it could maintain the constant hp. High torque rise engines "hang in a gear better". Modern class 8 engines are all high torque rise (though not quite constant hp). Electronic B5. 9 engines (24v and 3g in our trucks) are flat torque curve engines (to maximize the hp output through the cheapest possible drive-line -- higher torque capacity drive lines cost more). My original 96 215 hp Cummins had max torque at 2100 rpm (very annoying). I could hold a hill at 75 in 5th that I couldn't hold at 65. The 230 uprate from Cummins changed all that because it has a decent torque rise (for use in Trucks and RVs).