GST vs HST during a shift change

[Fallon]

where is torque multiplied in an hst. is there torque converter?

A HST is just a hydraulic pump directly connected to a hydraulic motor. Variable displacement pump so it can almost go instantly from 0 flow to full flow or anywhere in between. At 0 flow, the motors don't move, so they hold you at a stop. In practice they leak down a bit so depending on the gear the machine will creep a little bit.

Tractors have a clunky 3 speed transmission on them. Not actually sure if it's before or after the HST. Need to come to a complete stop to shift that tranny. No keep to stop to change speed within those 3 ranges. Some cheap machines out there only have a 2 speed tranny. Know a few machines like some mini TBLs that only have a 1 speed HST. I guess excavators & many skid steeres fall in that bucket as .

 

[ericm979]

The range transmission is after the HST on my Branson. The newer models have a four speed range trans with an H pattern shifter instead of the clunky in line shifter on mine. And it's got synchromesh so you can shift while moving. I think that applies only to the gear models though as the HSTs do not have a clutch. Being able to shift while moving would be really handy.

 

[Vigo327]

This is an old thread but going back to the beginning, if someone were to be curious about how an HST 'drives', the thing that probably most people can relate to is a riding mower. Most all modern ones are HSTs and essentially they function the exact same as an HST tractor, other than the aforementioned multi-speed trans that can be between the HST pump and the axle.

It's sort of ironic that newer tractors can have HST followed by a synchromesh gear trans, because if all the old gear tractors had synchros I'd barely see a need for HST in the first place. I know they have their strengths but im a car guy first and a manual transmission enthusiast and I for one don't mind shifting like mad even while doing FEL work with my little b6100. I just dislike not being able to change gears while underway except with extreme caution. Ive been moving ~120yds of dirt about 300-400 feet with my little tractors (gear b6100 & hst b8200) and I've been doing a lot of unsynchronized 2-3 upshifts while moving and getting that down. It's sort of fun as a challenge but if i could snap my fingers and put synchros in there i'd rather do that!

When im running the b6100 on this job it's L1+diff lock while pushing into dirt, then HR (high reverse), H2 to roll out, H3 when underway. So both gear shifting + range shifting + diff lock pedal going on. In the heavier HST b8200 it's just Low to push into dirt, High to travel and dump, and it doens't need the diff lock because its so much heavier (backhoe, filled tires etc). But the low-medium-high range shifter on the 8200 is so much more finicky and irritating to operate than both shifters on the 6100 that i don't enjoy using the HST tractor any more than i enjoy all the shifting of the 6100. So HST is not the only factor there.

 

[5030]

The downfall of all HST's (versus gear drive) is the parasitic power loss associated with the 'fluid drive' itself and why most require a frontal mounted heat exchanger, to get rid of the heat produced by the fluid coupling. Het produced in operation is wasted power.

Why I won't have one and prefer a hydraulic shuttle gear trans. Very little parasitic loss and residual heat produced.

 

[finn1]

The downfall of all HST's (versus gear drive) is the parasitic power loss associated with the 'fluid drive' itself and why most require a frontal mounted heat exchanger, to get rid of the heat produced by the fluid coupling. Het produced in operation is wasted power.

Why I won't have one and prefer a hydraulic shuttle gear trans. Very little parasitic loss and residual heat produced.

Not sure why people dwell on the power loss with a hst Transmission, especially on a light weight compact tractor that is traction limited. As far as I know, most manufacturers offer multiple power ratings within a frame size, but most customers, I think, based on what I see, chose the lower or intermediate power ratings, indicating that power isn’t a real issue.
For example, Kioti offers a CK2610, 3510, and 4010. Most of the ck series tractors seem to be, again, based on my observations, the lower powered 2610 or 3510. That tells me that power isn’t that big a deal to most. They are predominantly hst, too.

I personally have the 4010, and find that weight and traction are limiters, more than power is, with the hst.

The other thing is that most compact and even the larger utility tractors aren’t used much for pto work by the typical owner, especially since I don’t think the vast majority of owners are farmers whose primary income from working the land.

Even things like construction equipment are, for the most part, hydro.

 

[finn1]

The other thing to consider is the extinction of a manual transmission in light duty trucks and the trend towards automatics in medium duty trucks.

Manual transmissions were dropped from the Super Duty line, and eventually both competitors. It seems that the manuals cost more to build than an automatic, but commanded a lower market price, and has higher warranty costs, as well as lower torque capability, and lower resale value.

I suspect that the same is true with a non-hst tractor.

Medium duty trucks were at something like 60% market share automatic thirteen years Aho when I left the industry, and rapidly increasing.

 

[mikester]

Hst transmissions do not shift. They are a complete fluid drive. They do have 3 or 4 ranges at which to be operated but I personally only change ranges at a dead stop.

Pushing lightly on a hst pedal provides the highest torque value. Pushing the hst pedal to the floor creates the highest speed but lowest torque.

All variable speeds are created by different amounts of fluid flow combined with pressure etc. Hst works with a hydraulic pump creating flow and the flow is received down the line by a hydraulic motor. The pump is normally variable and the motor is normally fixed.

Some HST tractors DO shift. My M59/M62 has an electronic HI-LOW range lever that works for each gear.

So if I'm operating in 3-HI the HST auto shifts between LOW-HI depending on machine speed and throttle position. To answer the OP yes there is a slight but noticeable delay during shifting.

Skidsteers, CTL's, TLB's, wheel loaders all have some sort of HST shifting.

 

[finn1]

Some HST tractors DO shift. My M59/M62 has an electronic HI-LOW range lever that works for each gear.

So if I'm operating in 3-HI the HST auto shifts between LOW-HI depending on machine speed and throttle position. To answer the OP yes there is a slight but noticeable delay during shifting.

Skidsteers, CTL's, TLB's, wheel loaders all have some sort of HST shifting.

I don’t recall any delays when changing range on my CTL.

Does snap your head back, though.

 

[5030]

The other thing to consider is the extinction of a manual transmission in light duty trucks and the trend towards automatics in medium duty trucks.

Manual transmissions were dropped from the Super Duty line, and eventually both competitors. It seems that the manuals cost more to build than an automatic, but commanded a lower market price, and has higher warranty costs, as well as lower torque capability, and lower resale value.

I suspect that the same is true with a non-hst tractor.

Medium duty trucks were at something like 60% market share automatic thirteen years Aho when I left the industry, and rapidly increasing.

The main reason is today, the younger set don't have a clue how to operate a standard transmission. Had a devil of a time finding a puddle jumper with a standard transmission but I found one...finally.

I do know that now, if you get a CDL, it has to have a standard transmission cert on it, least here in Michigan.

I learned on an 18 speed twin stick and I'm good with a standard.

 

[finn1]

The main reason is today, the younger set don't have a clue how to operate a standard transmission. Had a devil of a time finding a puddle jumper with a standard transmission but I found one...finally.

I do know that now, if you get a CDL, it has to have a standard transmission cert on it, least here in Michigan.

I learned on an 18 speed twin stick and I'm good with a standard.

No, you don’t need to take your test with a manual to get a class A CTL in Michigan. You can take a test with an automatic equipped truck, but you will only be permitted for an automatic.

I doubt the same applies to a B license, since so many are now automatics.

Very few new cars are even offered with a manual anymore. They just languish on the lots because nobody wants them.

Same for light trucks. In fact, light trucks arguably led the way in eliminating automatics. The manual transmission is functionally obsolete in the marketplace.

And don’t blame it on the “younger folks”. My Bil is 68, my brother is 63, my meighbor is 72, the other neighbor is 79, none have ever driven a manual, at least not in the last forty years. I don’t think they’re atypical.