info Semi-powershift vs CVT

[Renze]

Valtra scored highest in a recent test of powershift tractors of around 210hp with their Versu automated 5 stage powershift.

This test was done with powershift models because depending on country, 20 to 80% of tractors in this power bracket are sold with powershift, and per manufacturer, the CVT vs powershift ratio differs per brand from 10 to 80%.

I assume Holland is a country where predominantly CVT is sold because i hardly see anything else in this class.

Hows the ratio CVT vs powershift in your country, and would a CVT be a requirement in order to sell tractors in this class ?

 

[diyfarmer]

I see sales figures for 2018 have been released here in Ireland by FTMTA, and of the 1,984 new tractors sold last year the most recent figures show that 94% of all new tractors registered have in excess of 100hp.
56% of new tractors have over 120hp, while 29% have over 150hp.

 

[Renze]

Interesting. That means 6% is less than 100hp, 38% is between 100 and 120hp, 27% between 120 and 150hp and 29% above.

I bet in Holland, Germany and France the market of 100-120hp models is a lot smaller, because part time farmers have plenty of used tractors to choose from...

 

[diyfarmer]

Most of the tractors I meet in my day to day routine would be 100 - 140HP, the only people with bigger ones are the big tillage contractors

 

[Renze]

Here in Holland you retire your main 130hp tractor to feeder duties and buy a new 180hp tractor for field work. This must be the reason why Zetor still sells in the Anglo-Saxon countries, while sales nearly halted in other Western European countries...

 

[Renze]

Anyways, my ideal powershift tractor would have a planetary Lepelletier style powershift with 7 ranges, each lower gear at 0.85 lower speed: it will give you a gear range for PTO l work like harrowing and rotavating of 2 to 5.33 kmh, a traction range of 5 to 13.3kmh (notice you can start at full traction at 5kmh) a grassland PTO work range of 10.5 to 27.8kmh (notice there is plenty of overlap to start with a heavy trailer in 2nd range, and shift to 3rd range and start 2 gears lower to make up for the momentum loss during range shifting, as well as starting in 3rd range when there is no load) and a transport range of 27 to 72kmh which gives 60kmh at 1850rpm.

 

[diyfarmer]

I don't know why if Zetor is putting a Deutz engine in a Crystal, that they don't stick the gearbox into them too. Or I test drove a Kubota and they had an interesting gearbox set up, the gearstick changed the different ranges and the splitter buttons bought it up and down the gears.

 

[Renze]

Yes, ZF had 6 ranges and two forward, one reverse gear since the late 70s. In the 90s they put a 4 stage powershift and a powershuttle in front of it, at the same time JD introduced the PowerQuad gearbox following that principle, and Case the Maxxum.

Current ZF gearboxes have 6 instead of four powershift ranges, and a wider spread between gears. Top gear gives 72kmh but is limited to 60kmh at 1850 rpm.

To really be a winner, you need to be able to take off with all four wheels spinning on the pavement in 2nd range, either to take off with a heavy trailer on a hill, or take off after a standstill in the plough furrow without lifting the plough. Then you need 2 gears overlapping with the 3rd range to make up for lost momentum during range change. Between 1st and 2nd you need just one gear overlap because you will come to a standstill changeing gear ranges anyways, and between 3 and 4 the momentum of the tractor is so big that it wont drop more than a single gearspeed during shifting from 3rd to 4th.

With too big powershift steps the engine doesnt run at peak efficiency, but with too small steps, taking off in a low gear just takes too many shifts, the shifting slows you down. The latter is the reason i have started to doubt dual clutch gearboxes in tractors, because tractors need finer ratio spacing than a Volkswagen, and both Deeres DirectDrive and VW DSG are not exactly faultless in real life. Therefor i think 0.85 ratio spacing and 7 powershift speeds, on a Lepelletier style epicyclic gearbox like ZF uses in automatic gearboxes for premium automobiles, is the optimum between engine speed, gear shift speed and comfort, and the ability to shift two speeds at a time when approaching a steep hill or sudden load increase.