Explanation of GST etc?

[hayden]

OK, I plead ignorance. Can someone explain the different forms of power shift, GST, etc.? I've driven manual transmission cars all my life and I can venture some guesses about how they have been improved for tractors that require constant shifting, but it would be just that - guessing.

Can you guys help fill in the blanks?

Peter

 

[kubmech]

GST (Glide Shift Transmission)...........

The GST uses a clutch pack that is spring released and hyd. engaged. It also uses a valve assy to shift the transmission gears. The range/gear selector chooses which gears shift, by a rotary valve in the valve shifter assy. The shuttle lever mechanically shifts from fwd and reverse but also dumps the hyd clutch pressure during the shift. All gear sets are synchronized to allow shift on the fly and smooth engagement.

Example: Shuttle lever and range selector in neutral, by moving the range selector to say 1st you are moving the shifter rotary valve and allowing hyd. power to a hyd shift piston in the valve which then engages the 1st/5th gear set. Because you are in the low range side 1-4, the range selector valve shift piston shifts the lo/hi range gear set to low range.
Now the clutch pack pressure has not been applied at this time
because the shuttle lever is in neutral. Moving the shuttle lever forward will mechanically shift to forward, once in the full forward position (shuttle shift rod also connected to shifter valve) clutch pressure is applied to the clutch pack, pressure builds, clutches engage and away you go.
Now your moving along in 1st gear and it's kind of slow for running down to the mail box so you move the gear selector to 5th. By moving the shifter you rotate the "rotary valve" which dumps clutch pressure and applies hyd pressure to the range select piston which shifts the hi/lo range gear set to high, you are now in 5th gear and the GST system did all the clutching and shifting for you.
Still not fast enough? shift to 8th gear. Rotary valve moves, dumps clutch, opens hyd passages to the shift pistons in the valve, they shift the 1-5 gear set to neutral and shifts the 4-8 gear set to engage and leaves the hi-lo gear set in high range giving you eighth gear.

HYDRAULIC SHUTTLE:
This system also has a clutch pack and a valve, but is much different. The only purpose of hyd shuttle is to make it easier to shift from forward and reverse. It has a single clutch pack with two seperate sides one for fwd and one for reverse. Moving the shuttle lever to neutral dumps clutch pressure to both sides of the clutch through the shuttle valve. The shuttle valve is controlled mechanically by the shuttle lever. Moving the lever to fwd applies hyd power to the fwd side of the clutch pack which engages the forward gears or reverse respectively. All gear/range shifting is done manually.

Both of these systems have a series of relief valves, modulators and accumulators built into the system to allow for smooth clutch engagement.

 

[rbargeron]

Kubmech - That is a fine job of explaining what's going on in a GST and Hyd Shuttle - I always learn something when I read your posts -Thanks for the time and knowledge you give to all of us - it's great. /w3tcompact/icons/cool.gif

Dick Bargeron

 

[tdean]

Interesting info. I'm wondering, Kubmech (or others), if you could comment on the 8F-4R shuttle that Kubota now offers in the M4900. Any ideas about how 4 fewer reverse options might affect operation? As always this site is a learning experience.

 

[kubmech]

Well.. They probably caught themselves. Some of the older 8 speed tractors had a lock out for the higher gears in reverse. Most likely a saftey/Liability issue. Took a quick look at the M4900 book and noticed that it shows 8 speeds in reverse. But the sales pamphlet shows 8-4, unless you get the creep gear then it's 12-4. Can't imagine it really affects performance
as 4 hi should be plenty fast enough for reverse. If you have to go that far, turn around./w3tcompact/icons/wink.gif

 

[hayden]

That's great, thanks. It sounds like the automatic stick shifts in the old VWs.

Let me play it back strictly from an operator's perspective.

- I gather there's a foot peddle for the engine speed so you can vary it more easily like in a car. There's also a fixed speed lever like on an HST for extended run times at constant speed.

- The speed range gear selects the gear you want, with two or more ranges available.

- The column-mounted lever on the left is the F-N-R lever.

- No clutching is required except for engine starting and presumably PTO engagement.

- Moving the F-N-R lever from N to F with make things start moving after some delay.

- Moving F-N-R back to N puts the tractor in a glide (equivalent to manually clutching)

- Same for Reverse.

- Once in F, the gears can be changed by just shifting the lever on the fly without any manual clutching

- Presumably you can manually clutch, place the F-N-R lever in F, then work the clutch to ease forward just like with in my car.

- Shuttle shifts have the F-N-R part, but changing speeds requires the old-fashon kind of clutching. I assume the gears are synchonized?

Did I get this right. It's actually quite an impressive system, but doesn't sound any less complicated than an HST's internal workings. In fact, HST might be simpler.

Are there other types of transmissions (exclusing the car-like ones), or are they all the same thing with different manufacturer's branding.

I guess it brings me right back to the other question - why not HST everywhere? GST seems to have the same if not greater complexity.

 

[kubmech]

Sounds like you have the idea, Theres no need for a "cruise control" lever like some of the HST's have. Yes you can manually clutch if you choose to but that's due to the good old fashion dry clutch and pressure plate prior to the clutch pack. The clutch should be used when shifting the pto. Shuttle shifts are synched. Why GST over HST? Well I geuss it's operator preference. From a mechanics standpoint HST is much simpler than GST and Shuttle due to the valving and all the extra gears to deal with.
HST is pretty much self contained with a lot fewer moving parts and you only have the range gears to deal with.

 

[njrqs]

Once again Kubmech has come up with the goods when trying to explaing something to us!!! - Keep up the good work.

Those transmissions sound mighty fine for an operator of an old clunker with regular transmission. Mine is a pain and I don't have a FEL. I can imagine the new transmissions would make that sort of work a breeze !

Cheers

 

[grandad]

Just test drove a 3010GST for the first time at local dealer. Appreciate your explanation of what all was going on down there. Sure is different than that old Super M I used 35 yrs. ago.

Dealer says GST is a true direct gear drive, unlike HST. Goes on to say it's a bit more efficient, maybe a slight advantage for applications where you need all the power you can get to the wheels. But HST is the real deal for anything like loader work, etc. where there's lots of back and forth.

I wonder if the experts here have an opinion about how much power loss there really is with HST. Enough to make any real difference?

New user... greatly enjoying the forum.

 

[Bird]

Grandad, I don't know, personally, how much power is lost to the HST, but I've read 10-15%. And since an HST usually has enough power to spin the wheels, you couldn't use anymore power unless you also increased traction (which of course is always possible). So in my opinion, at least for me, it isn't enough to make any real difference.