HST Power Consumption

[CJONE]

OK so I finally get enough money together to buy the 45HP tractor that is recommended for the range of jobs on my size acreage.

Then I find out that 9 to 13.5 HP will be consumed by a HST transmission.

That's OK ; just spend even more cash to size up to a 55 to 60 hp to accommodate that loss of power.

But wait there, that size of machine ( HST or Gear) is, for me, just too large to work in those tight places: the narrow creek crossings and tree plantings that separate large open fields.

Firstly, I want the HP I need but I also want a size machine that can be operated efficiently and conveniently in a fair range of conditions.

If you run the HST at lower flow/pressure the efficiency increases so don't sweat it. I was just tring to make a point that a HST will use more than 1.5HP. CJ

 

[CJONE]

I'd love to see some proof of this.

See post #51. Also why is there either a dedicated HST cooler or a larger one with a HST equipped tractor. Simple answer, something has to be done with the added heat generated by the HST, The heat was generated by lost HP. With all this being said give me a HST over gear anyday. CJ

 

[CJONE]

I don't know if anyone else has noticed this but with my HST when I start the engine and it's running at a fast idle 1200~1400 rpm) if I move the loader or raise the 3pt and put a load on the hydraulic pump the motor will load down. It doesn't matter how slow I try to raise the loader it still loads the motor. But when you use the HST it doesn't unless you push the HST pedal to the floor (which would be like trying to drive in top gear at idle in a gear tractor. Just an observation.

Cold fluid in the hydros takes more hp to raise a implement. A hydrostat will only use as much HP as needed to get the job done. Put the hydro in high range and it will lug the engine with just a little bit of pedal. CJ

 

[SPYDERLK]

The hst pump/motor combination, separate from any geared range mechanism, is infinitely variable within it's own range. So if you push the pedal down 1/3, for example, you are getting an "effective" gear ratio that is 1/3 of the highest available. (The available range can be played with by specifying different displacements for the pump/motor.) So effectively by moving your foot you are choosing an input/output ratio.

The "safe" limit in a hydraulic system is mostly determined by how much you want to spend on the robustness of parts. If you want to go all out and use super strong hoses, fittings, coolers, valves, pumps, etc., then you can use a relief that is much higher.

Combine those two facts and the result is that an hst system can be designed to put down as much torque as you want and effectively geared as low as you want. You want enough torque on the ground to slowly spin the treads of the biggest track hoes... it can be done. Maybe your BX can't do deliver as much torque as its geared twin. But please stop suggesting that there is some quality inherent in hst systems that automatically prevent them from ever transmitting as much torque as a geared system can. After all, a gear box must be engineered to handle some design goal amount of torque too, and as it can be, so too can an hst system.

xtn

+1 CJ1

No. Designed for any given maximum sustained force application and with customary safety factors for each, the gear will always be able to work beyond the point where the HST will not. -At the point where the HST cannot make its wheels turn to get you out of the hole [traction assumed], the identical gear platform having 10% less HP will get you out. - The issue is that direct gearing makes one for one use of all energy stored and produced by the spinning engine whereas at limit the HST flushes it thru a valve to sump. The HST must have this automated safety because of the variable pump. It camouflages how much pressure is being produced by allowing the engine to seemingly spin freely. This is inherent. With direct gearing you are quickly aware when the trans is working hard because the engine tells you. Safety factor there is just component strength built in as some multiple of full engine torque input to the gear train. Probably about 3X.
...-2.
larry

 

[CJONE]

No. Designed for any given maximum sustained force application and with customary safety factors for each, the gear will always be able to work beyond the point where the HST will not. -At the point where the HST cannot make its wheels turn to get you out of the hole [traction assumed], the identical gear platform having 10% less HP will get you out. - The issue is that direct gearing makes one for one use of all energy stored and produced by the spinning engine whereas at limit the HST flushes it thru a valve to sump. The HST must have this automated safety because of the variable pump. It camouflages how much pressure is being produced by allowing the engine to seemingly spin freely. This is inherent. With direct gearing you are quickly aware when the trans is working hard because the engine tells you. Safety factor there is just component strength built in as some multiple of full engine torque input to the gear train. Probably about 3X.
...-2.
larry

I have never been there yet, the HST at very low speeds, lower than a gear tractor will go. [unless it has a very deep reduction] Will bury itself. When the relief opens you still are building pressure at the relief setting so the engine tells you as you said by listening to it. As far as direct gearing being 100% efficient, no not hardly. It still generates heat and that is from HP being wasted to friction. Is a gear trans more efficient, you bet. Easier to run, no. More durable, depends on the operator. So it all comes down to operator preferance. CJ

 

[xtn]

No. Designed for any given maximum sustained force application...

I rest my case.

Yes, due to inefficiencies you will need a more powerful engine with hst, but as a drive line system including the engine, either system type can be designed to produce X maximum power to the ground.

So please specify exactly which part of my previous post you are saying "no" to.

xtn

 

[SPYDERLK]

I rest my case.

Yes, due to inefficiencies you will need a more powerful engine with hst, but as a drive line system including the engine, either system type can be designed to produce X maximum power to the ground.

So please specify exactly which part of my previous post you are saying "no" to.

xtn

Where you said inherent. Design for design to a force spec the gear will stop after the HST. Also, I said nothing about 100% efficiency. At this level of discussion I regard std mechanical inefficiency as assumed. Only where special situations exist need they be drawn apart.
larry

 

[crazyal]

OK so I finally get enough money together to buy the 45HP tractor that is recommended for the range of jobs on my size acreage.

Then I find out that 9 to 13.5 HP will be consumed by a HST transmission.

That's OK ; just spend even more cash to size up to a 55 to 60 hp to accommodate that loss of power.

But wait there, that size of machine ( HST or Gear) is, for me, just too large to work in those tight places: the narrow creek crossings and tree plantings that separate large open fields.

Firstly, I want the HP I need but I also want a size machine that can be operated efficiently and conveniently in a fair range of conditions.

There's a real difference between real world and theoretical differences. In the real world there are very few times where you notice a difference between the two power wise. Most times I've seen a tractor that had so much traction that it couldn't spin the tires yet enough power not to stall, guess what happens? The front end lifts off the ground, lots of YouTube videos. When it can't it spins the wheels or stalls the engine.

For the very few times where the gear tractor could keep moving without spinning the wheels. All one would need to do is slow down a little with an hst and hp will not be an issue. That's why people always say that gear tractors work best for things like pulling a bottom plow. However most people are willing to trade off that advantage for all the hst advantages.

 

[dusty3030]

HST is the work of the devil. The whine of the HST is actaully the banshee scream of beezlebub. Clutches make you tired and humble so you will stay out of mischief I tell you.

 

[BeeferMan]

There's a lot of interesting information in this thread - some of it is probably even true, lol...

But as for which is better or more desirable, HST or geared, that question is impossible to answer unless you specify the job to be done. Comments such as "give me a HST over gear any day" just don't make sense. If, for instance, the job is pulling plows all day long at constant speed where maximum fuel efficiency is important a geared machine is probably the better choice. If you're loading all day long, or working back and forth in tight quarters then an HST is more likely the way to go.

Lots of things "steal" HP from a tractor - power steering, a loader, 4wd, A/C - deciding which of these "power drains" makes the job at hand more efficient is going to be different for different tasks. Choosing the right tool for the job is the sign of someone who knows what they're doing!