HST questions

[broncobilly_69]

Hi everyone. I recently bought a new Grand L5460 and had a question about HST operation. Is it generally considered best to use a lower gear and more pedal (perhaps easier on the pump due to mechanical advantage), or, if not operating on a hill or using a plow type implement, is being in a higher gear and using less pedal better (perhaps not requiring as flow of fluid? Does one help flud temps more than the other??
How about the hi-lo switch is easier on any components to have it one way versus the other? Does it actually change a gear ratio or just something with the pump? Currently, I have been going with more pedal in a lower gear.
thank you for any insight. I tried reading the WSM, but I'm not sure I'm smart enough to fully understand the operation and the ops manual doesn't really cover it.

 

[BruceP]

The engine RPM should be high enough so the pump/motor are not 'struggling' to do their work. It is FARRR more efficient to use higher RPM instead of forcing the pump/motor to overwork.

Obviously, if you are pulling a load, the engine RPM should be in its most efficent range. (It consumes MORE fuel to run lower RPMs and put higher load the engine)

Additionally, keeping the engine RPM up will reduce the frequency of parked-regens. This is becasue running more hot exhaust gas thru the system helps burn off impurities.

 

[broncobilly_69]

The engine RPM should be high enough so the pump/motor are not 'struggling' to do their work. It is FARRR more efficient to use higher RPM instead of forcing the pump/motor to overwork.

I always keep The engine RPMs over 2,000. With the HST I can maintain the same RPM in any gear going any speed.

 

[lynnmor]

The engine RPM should be high enough so the pump/motor are not 'struggling' to do their work. It is FARRR more efficient to use higher RPM instead of forcing the pump/motor to overwork.

That "struggling" might better be defined as torque. For example; two systems doing the same amount of work, where one is turning twice the RPM, will have about double the torque on the slower one. While torque is often thought of as a good thing, it really means that every gear tooth, vane, clutch and shaft will have twice the load.

 

[jimh406]

There is overlap between L, M, H range. Assuming the RPMs are the same, you can go the same speed with both M and L, for instance. In L, you might have to use maximum pedal while in M just part way. The HST will tell you by it’s sound or whine how efficient it is working.

Think of pressing the pedal as switching transmission gears in a manual transmission but you have unlimited gears in the HST. The more you press the higher transmission gear you go to. So, if you hear the HST whine, sometimes using less pedal will allow you to accelerate while more pedal will just cause whine.

You have to really work the engine to bog down the RPMs. Of course, there is a visual indicator with the tachometer for RPMs. If you find you are bogging the RPMs, you should probably switch to a different gear range or if in L use less pedal.

Finally, you’ll have more control to slow down at a lower range. That can be important going down hill. In that case, L would be better than M.

 

[BruceP]

That "struggling" might better be defined as torque.

Agreed - I hesitated to bring 'math & physics' into the discussion.... some people do not understand this stuff.

Said another way. When the amount of POWER delivered to the wheels is the same, it can be done two ways:
(high RPM with low torque) = (low RPM and high torque)

Anyone who has ever pedaled a bicycle in the wrong gear has experienced this phenomena.

In nearly EVERY case, there is less stress on the bearings, shafts, couplings, and other mechanical parts as the torque is reduced. This is why higher RPMs are desirable.

It does not matter if we are talking hydraulic pressure (HST), or mechanical gears.
(Low pressure with more flow) = (high pressure and low flow)
It is better to use lower pressure than high pressure to get the same amount of work done.

------
As an aside, electricity behaves EXACTLY the same way.
For a given amount of POWER, electricity can be delivered two ways:
(low voltage with high current) = (high voltage with low current)

In the case of electricity, there is MUCH less loss over long distances if the POWER is transferred at high voltage (1000s of volts). Also, the lower current requires smaller conductors which is FAR less expensive over many miles. At the delivery point, the voltage is dropped back down to more freindly voltages before being deliverd to your house. All the time, the POWER is the same.

In the end POWER is POWER no matter what form it takes.
Infact, if I recall correctly: 1 Horsepower = 746 Watts

 

[Henro]

That "struggling" might better be defined as torque. For example; two systems doing the same amount of work, where one is turning twice the RPM, will have about double the torque on the slower one. While torque is often thought of as a good thing, it really means that every gear tooth, vane, clutch and shaft will have twice the load.

This is true up to the point where the driveline cannot be changed. For example, for a given ground speed the output shaft of a transmission will have to turn at a certain RPM. This relationship is a constant, independent of engine RPM and transmission gear ratio. (in other words, gear ratio and engine RPM produce the same output shaft RPM,for a given ground speed, regardless of how they are proportioned.)

Changing engine RPM and transmission gear ratio does nothing to affect the stress on the components from the transmission output shaft onward.

Just splitting hairs…. Like Linnmor I’m in the run at higher RPM crowd.

 

[CGMKCM]

My 4760 lives in the Medium Hst setting and I use the hi/low stick to regulate speed/pushing power for loader work. I also set the throttle 2000 - 2200RPMs. I think Messicks has a video on HST operations. I remeber L= loader, M=mowing and H=highway.