Power Converted To Heat?

[Maine farmer]

I was looking at some tractor specifications, and I notice a lot of engine horsepower is lost in the transmission, which I presume is lost to heat generated by friction.  ( the power must be going somewhere )  For example one tractor in particular that we own has engine horsepower of 85, but the power take off horsepower is 75, which obviously means we lose 10 horsepower in the transmission.  

 

My last physics class was a long time ago, so I can't quite remember how I would go about calculating how much heat would be generated by the transmission using the tractor at rated output.

 

 

[Turtle]

I was looking at some tractor specifications, and I notice a lot of engine horsepower is lost in the transmission, which I presume is lost to heat generated by friction.  ( the power must be going somewhere )  For example one tractor in particular that we own has engine horsepower of 85, but the power take off horsepower is 75, which obviously means we lose 10 horsepower in the transmission.  

 

My last physics class was a long time ago, so I can't quite remember how I would go about calculating how much heat would be generated by the transmission using the tractor at rated output.

 

Wouldn't the heat generated calculation depend on many specifics such as type of metals, areas of contact, speed, viscosity of fluid, etc.? I think calculations could at best give an estimate, and that testing would be required to find actual values. :shrug:

Edited July 19, 2017 by Turtle

[Maine farmer]

Wouldn't the heat generated calculation depend on many specifics such as type of metals, areas of contact, speed, viscosity of fluid, etc.? I think calculations could at best give an estimate, and that testing would be required to find actual values. :shrug:

Well, I guess perhaps I was over simplifying by just thinking about a direct conversion from HP to BTU, (of course to be more modern and global KW to calories)

 

The only specific thing I know off the top of my head is the power take off speed is 540 rpm with an engine speed of 2100 rpm.  And the transmission/hydraulic fluid is John Deere Hyguard brand.

Edited July 19, 2017 by Farming guy

[Turtle]

Well, I guess perhaps I was over simplifying by just thinking about a direct conversion from HP to BTU, (of course to be more modern and global KW to calories)

 

The only specific thing I know off the top of my head is the power take off speed is 540 rpm with an engine speed of 2100 rpm.  And the transmission/hydraulic fluid is John Deere Hyguard brand.

HP is fine. It's what we use and if others want a conversion to other units they can darn well do it themselves. :lol:

 

Anyway, here's what looks like a fairly good article. Though it is more specific to autos than tractors, the same principles apply.

 

Drivetrain Power Loss

... The fact of the matter is every vehicle experiences different levels of drivetrain loss as determined by the design of its transmission and driveline components. Simply put, the amount of horsepower lost to the forces of inertia, drag, windage, pumping and friction are different for every engine, transmission and driveline design.

...

Within the drivetrain, steady-state power losses occur from the following components: the transmission torque converter (in the case of automatic transmissions), the transmission oil pump, clutch pack drag, one-way clutch drag, seal and bearing drag, gear windage and friction, and final drive losses.

 

Dynamic drivetrain losses, on the other hand, include the rotational inertial losses from angular acceleration occurring within the drivetrain while accelerating. In fact, during acceleration there are losses from the rotational inertia of spinning transmission and differential internals as well as driveline components like driveshafts and prop shafts, but also from the increased load and friction being generated between the gears within the transmission and differential(s). And as you already know, with increased friction comes increased heat (more on that later)

...

[Maine farmer]

HP is fine. It's what we use and if others want a conversion to other units they can darn well do it themselves. :lol:

 

Anyway, here's what looks like a fairly good article. Though it is more specific to autos than tractors, the same principles apply.

 

Drivetrain Power Loss

Much thanks for the link.  Very interesting.

[JMJones0424]

I was looking at some tractor specifications, and I notice a lot of engine horsepower is lost in the transmission, which I presume is lost to heat generated by friction.  ( the power must be going somewhere )  For example one tractor in particular that we own has engine horsepower of 85, but the power take off horsepower is 75, which obviously means we lose 10 horsepower in the transmission.  

 

My last physics class was a long time ago, so I can't quite remember how I would go about calculating how much heat would be generated by the transmission using the tractor at rated output.

 

Isn't this just a simple unit conversion problem?  I think it's safe to presume that the loss in power between the engine and the PTO is due to heat losses.  There are certainly other factors to consider, such as sound generation, but I don't think that these factors are significant.  As such, all you are asking is how to convert 10 hp to a measure of heat.

 

Horsepower is a measure of power, the rate at which work is done.  Heat is the flow of energy between two objects outside of work.

 

10 hp is roughly equal to 7460 watts or 7460 Joules/second or 25440 Btu/hr.

 

25,000 Btu is no joke.  My bedroom is cooled by a 12,000 Btu air conditioner.  Your tractor's transmission must shed this heat or it will ultimately overheat and fail to operate.  This is the reason why it's so important to regularly clean your equipment.

Edited July 26, 2017 by JMJones0424

[exchemist]

 

Isn't this just a simple unit conversion problem?  I think it's safe to presume that the loss in power between the engine and the PTO is due to heat losses.  There are certainly other factors to consider, such as sound generation, but I don't think that these factors are significant.  As such, all you are asking is how to convert 10 hp to a measure of heat.

 

Horsepower is a measure of power, the rate at which work is done.  Heat is the flow of energy between two objects outside of work.

 

10 hp is roughly equal to 7460 watts or 7460 Joules/second or 25440 Btu/hr.

 

25,000 Btu is no joke.  My bedroom is cooled by a 12,000 Btu air conditioner.  Your tractor's transmission must shed this heat or it will ultimately overheat and fail to operate.  This is the reason why it's so important to regularly clean your equipment.

Yes, my rule of thumb is 1kW is one bar of an old-fashioned electric fire. 7 of these is quite a bit, but losses of this magnitude seems to be quite normal for some types of transmission, especially those involving a torque converter or a fluid coupling. If it is purely mechanical drive I think I'd be slightly surprised to lose that much.

[Maine farmer]

 

 

25,000 Btu is no joke.  My bedroom is cooled by a 12,000 Btu air conditioner.  Your tractor's transmission must shed this heat or it will ultimately overheat and fail to operate.  This is the reason why it's so important to regularly clean your equipment.

Well, yes, the transmission/hydraulic oil does get quite hot, thus the large oil cooler at the front of the tractor.  Modern tractors ask for a lot out of hydraulics, powering not just front end loaders and lift cylinders on implements, but motors as well.  I remember one old  tractor that had a pump that put out only 12 gallons per minute, and most of the new ones put out at least twice that, even with a smaller pump!

 

Our oldest tractor ( made in 1973) has developed an internal leak that generates enough heat to actually start breaking down the oil if run at capacity for as little as an hour.  Since we would have to split the tractor and dismantle the transmission to find the leak, we have semi-retired that tractor to feed wagon duty until we can have the time and money for a proper repair.  I was using it to run a 12 foot wide mower, and the oil turned black and clogged the filter. I couldn't even touch the filter housing for about an hour.

[exchemist]

Well, yes, the transmission/hydraulic oil does get quite hot, thus the large oil cooler at the front of the tractor.  Modern tractors ask for a lot out of hydraulics, powering not just front end loaders and lift cylinders on implements, but motors as well.  I remember one old  tractor that had a pump that put out only 12 gallons per minute, and most of the new ones put out at least twice that, even with a smaller pump!

 

Our oldest tractor ( made in 1973) has developed an internal leak that generates enough heat to actually start breaking down the oil if run at capacity for as little as an hour.  Since we would have to split the tractor and dismantle the transmission to find the leak, we have semi-retired that tractor to feed wagon duty until we can have the time and money for a proper repair.  I was using it to run a 12 foot wide mower, and the oil turned black and clogged the filter. I couldn't even touch the filter housing for about an hour.

Ah OK so it is a hydraulic circuit, not just a mechanical linkage.

 

In that case I'm not surprised you have losses of that magnitude.

 

As an ex-lubricants man I wince a bit at your description of what the internal leak is doing to the oil. Sounds like it is oxidising badly - it must be getting very hot and presumably is in contact with air somewhere in the circuit.   

[Maine farmer]

Ah OK so it is a hydraulic circuit, not just a mechanical linkage.

 

In that case I'm not surprised you have losses of that magnitude.

 

As an ex-lubricants man I wince a bit at your description of what the internal leak is doing to the oil. Sounds like it is oxidising badly - it must be getting very hot and presumably is in contact with air somewhere in the circuit.   

Direct mechanical power linkages are becoming a rare thing in tractors, and I have learned that one way to detect internal leaks earlier is to run the tractor for a bit, and then check the transmission dipstick for bubbles using a magnifying glass.  I wonder how much damage I could have prevented, as I can only imagine what the inside of the hydraulic pump must look like by now.