info Some Zetor gearbox ideas..

[Renze]

I have been thinking: I have been a firm believer of DSG technology because it needs only dual clutches (and two directional clutches) that cause drag loss, instead of 11 for an 18 speed full powershift.

However, VW DSG transmissions dont quite have a good name after doing 200.000km... When clutch packs wear, it starts to shift rough. People choose a conventional automatic for luxury or a manual transmission for reliability and lowest cost of ownership... Deeres DirectDrive, i hear bad rumor about their practical use (shift speed adaption on hills in particular, it stalls because it cant downshift fast enough when backing a trailer up the silage heap) so the old powershift transmission is still the most reliable.

So, heres my idea: We use the Zetor three speed powershift module, and hang a single clutch pack besides it: the 3 speed powershift will shift stages 1, 2 and 3, then the single clutch pack will shift stage 4: Then the shift module behind the 3 stage powershift changes range, and the parallel stage 4 clutch is released and the lowest step of the powershift engages again: then again the 3 stage module can make 3 shifts, stage 5, 6 and 7.

With the Forterra ratios of 0.865 per powershift step, this 7 speed powershift would have the same ratio spread as the MF Dyna6 transmission. So, lets start at 50kmh, it will run 21kmh in 1st powershift, range 4. The 3rd range will start at the same speed 21kmh (one overlapping gear) and 1st powershift, range 3 will give us 8.8 kmh. Then we have a tillage range 2, which spans the tillage working speeds of 4.25 to 11 kmh. The overlap will be bigger between range 2 and 3 because you dont want to shift ranges with the plough in the ground, the tractor will come to a standstill and will not be able to take off in 3rd range under full load.. Therefor we need to get the tillage range up to 11kmh, if the plough pulls so easy that it can pull it faster than 11kmh, the draft requirement of the particular implement is low enough to take off in 3rd range at 8.8kmh with the implement in the ground..
Then we have a PTO tillage range 1, from 1.8 to 4.5 kmh, also with one overlapping gear.

this would be a development path with a failsafe included: if the DSG part would not function with claw clutches, it could be replaced by disk clutches down the road. And the most important feature: It only requires "dumb" black and white shifts, just like the current 3 stage powershift unit: The ranges preselect without power, because the 4th gear is an intermediate gear which disconnects the 3 stage powershift unit for preselection of the next gear. The software could release pressure from an accumulator (piston, membrane doesnt last) to quickshift the range, while the transmission oil pump is only used to engage the other clutch pack on the 3 speed powershift unit...

Practical result is that you get a 7 speed gearbox that only shifts one clutch at a time, smooth without modulation, just simple shift logic.

It is quiet around Zetors DSG gearbox, consisting of the 3 speed powershift unit with a 4 speed DSG range behind it, e.g. creating a 12 speed gearbox which has a lot of time to preselect the ranges (required every 4th shift) when shifting straight up or down. It has little benefit when jumping up and down between step 3 and 4, then still quick range preselect changes (which seem to be difficult for Deere) are required. Als the patent they have, on a DSG shuttle shift transmission doesnt work (both shafts are occupied to make the gearbox reverse so the drive must be interrupted to change gear reversing), and their first functional prototype combines the price of multiple clutch packs with the added difficulty of shifting a range and the powershift at the same time, whilts having only the benefit of more time between range changes when you run straight through the gears, not move up and down between 3 and 4 (which one, based on what parameters should the computer decide to preselect ? There will still be a dead shifting spot in the gears) Therefor i think the 3 stage powershift with two powershift ranges behind, with an intermediate gear on a paralel shaft to allow single clutch shifts between every gear, will be worth investigating, and perhaps a lower risk development...

 

[Renze]

Case and New Holland already announce the sales date of their 8 speed DSG gearbox:

Case IH Maxxum gets dual-clutch, 8-speed powershift option - Agriland.ie

ActiveDrive 8 from Case IH offers eight powershift steps in each of three ranges, providing a total of 24 speeds in both forward and reverse.

www.agriland.ie

This ratio spacing and reach is similar to Deeres, and most ideal. Full traction available in 2nd range 1st gear. Shift from 2 to 3rd range is at high enough speed to make sure the momentum keeps rolling while the range is changed.

If zetor wants to use two clutches like they patented, they would need a mechanical reverser for each individual secondary shaft to make it able to powershift in reverse.

If they want to make a low tech semipoweshift without shift modulation they can use the idea in my previous post...

 

[Renze]

Deutz has the new ZF gearbox with 6 powershift steps and 5 ranges, 18% speed difference between the powershift steps and at least 2 steps overlapping. It has a max speed of 72kmh for very low engine rpm at cruise speed.

This has an advantage over the Deere directdrive because the steps are smaller than Deere, so easier to maintain PTO speed whilst accelerating with a mower. Deere has reasonably big steps in order to not make the tractor accelerate faster than the DSG can preselect.

If the 7 speed powershift idea is to be used, perhaps its better to use 4 gears and high and low range.
A very beneficial feat of the Deere DSG transmission is that it can drive off at 4.2kmh where the wheel torque exceeds the traction limit of a ballasted tractor on concrete. 3 gears x 7 powershifts would span that ratio (72kmh x 28 steps minus 6 overlaps is 3.4 kmh)

Then when we start a field range with sufficient headland speed, at 7kmh, we would get crawl speeds as low as 0.33kmh.

If they see 60kmh road transport at reduced engine rpm as no benefit (tire wear increases exponentially above 40kmh) they could also take 60kmh as top speed at 2200rpm (41 at 1500rpm) they could do with three main gears, stretching from 60 to 5.7kmh with 7 powershift steps. At 5.7kmh and 2200rpm would mean a 10 ton ballasted tractor will be spinning its tires at 1100rpm with 75hp at 1100rpm. So thats sufficient to take off with any load in high range, and thats clearly what we want when pulling a trailer off a wet field, or continue ploughing after making adjustments in the furrow.

The 3 gears and top speed 60 means also that you get 7 uninterrupted speeds from 5.7 to 13.8 kmh which is most ideal for tillage.

Whatever Zetor does, they must show something on the Agritechnica and start taking pre-orders or they better go home. Ground once lost, is very hard to re conquer as a small player in a competitive market


Here an essay about transmission losses:

http://www.sciencedirect.com/science/article/pii/S1537511008000846

It writes that the biggest losses are caused by high speeds of the gearwheels of the lower gears, when the higher gears are used. The idea of ZF, of putting the synchromesh coupler of the lower gears on the layshaft and those of the higher gears on the topshaft, to reduce idle gear speed, makes a lot of sense.

And here something by Daf trucks about making the ZF AS Tronic powershiftable in the cruise gesrs

http://www.mate.tue.nl/mate/pdfs/5999.pdf

 

[Renze]

Heres another great transmission: The 1975 Allis Chalmers 6 speed powershift which is layd out do that each shift is made with one clutch pack only: its the smoothest and most durable method of powershifting available. The Allis Chalmers transmission had 6 forward , one reverse with hi and low range to make a 12F/2R transmission but its steps are twice as big as what 2017 requires: also, smaller steps make smoother shifts.

I like the idea as it tackles the weakness of the NH TM and Case Magnum powershifts (3 clutch shifts from 6 to 7 and from 12 to 13) by ground design, instead of by proportional control of shifts which only burn clutch packs...

US3929037A - Six speed power shift transmission - Google Patents

A six speed power shift transmission having three planetary gearsets and a countershaft gearset with one of the planetary gearsets providing a reverse gear drive. The shifting is accomplished by five hydraulically actuated clutches and one brake to provide six forward speeds and one reverse.

www.google.com

 

[diyfarmer]

I drove a grand tractor lately had only 3 gears low, mid and high but with 8 splitters in each range, on a button, all on the same gearstick on right hand on the seat. a short gearstick no big movement, a simple h shape. A Kubota M6 range.

Would be nice on a Zetor too.