Machinery

John Deere DirectDrive gearbox on test

Friday 19 October 2012 11:00

It’s fair to say John Deere has lagged behind a bit in the gearbox stakes over recent years.

While nearly all the other main players in the tractor game have set about developing, with varying degrees of success, semi-powershift transmissions that’ll slot in between ultra complex CVTs and bog-basic mechanical boxes, the green giant has dragged its feet somewhat.

The company has always maintained that between its idiot-proof AutoQuad stick-shifter and silky smooth AutoPowr stepless box, operators have had plenty of choice.

Now it seems that has changed – Deere has developed its own lever-free shifter. We got the chance to try out an early evaluation model alongside two tractors with existing semi-powershift and CVT gearboxes.

 John Deere 6R

How it works

With the Direct Drive box, Deere is hoping to get the best of both worlds – the simplicity of an AutoQuad combined with the butter-smooth operation of an AutoPowr.

On the face it, the box does look pretty simple. At the back it’s got three mechanical ranges that are selected using three buttons on the main console. These are then split into eight individual gears that feel a bit like powershift steps to the driver.

But the difference is that there are actually eight cogs between the ranges, rather than clutch packs or planetary gearsets.

These gears sit on two separate shafts - one holding the even gears and the other home to the odd. Each shaft also has its own clutch, meaning shifting between the two is almost instant.

For drivers that like to stay involved, the eight speeds can be manually shifted, but there is also a fully automatic mode.

This is where things get a bit more complicated. The electronic witchcraft that controls the gearbox is constantly monitoring whether you’re accelerating or slowing down and preselects either a higher or lower gear accordingly on the shaft which is running idle. Then when it senses the revs and load are right it switches clutch-packs to put drive through the preselected gear.

Because there are true gears to be shifted, it isn’t as smooth as an AutoPowr, but in theory it should sap less power.

 John Deere DirectDrive

Setting it up

Just like the AutoPowr, the transmission home page has a label-less vertical scale similar.

The green bar that makes up most of the scale signifies engine rpm. A blue arrow shows eco engine speed – the minimum engine rpm when you’re up to speed. Possible because the transmissions are actually rated to 65kph, the tractor will continue to climb up the gears while cutting engine rpm to the set Eco speed.

Deere calls the white arrow the “auto shift engine speed droop”. In layman’s terms that’s the downshift point – when the tractor will decide to drop down a gear as the engine labours.

In full auto mode the tractor will adjust these settings according to the load and speed – all the operator has to do is drop his size 10s on the pedal – but they can also be customised.

The downshift point can be adjusted as a percentage of max engine rpm. With the pto off this can be as high as 40%, but with the pto spinning it’s likely to be a fair bit lower. The eco speed can be changed, too.

We’d prefer to see these figures set as actual engine rpm rather than a percentage. The settings could also be simplified by just offering low, medium and high options.

Driving it

In truth, the new box behaves pretty much the a CVT from a driver’s perspective, the only difference being that before setting off you select one of three ranges – A, B or BC – with orange buttons alongside the AutoPowr-esque lever.

It’s in its usual Auto slot for most of the time but knock it left and you go into manual mode. Nudge it forward for an upshift and back to drop a cog – much like a TipTronic box.

And similarly to an Audi, the use of the double-clutch set-up has made gearshifts silky smooth. However the Deere box isn’t immune to the standard scourge of semi-powershift transmissions – there are long pauses between range changes. You certainly don’t want to shift when under load in heavy draftwork – any forward momentum is instantly lost and the abrupt halt leaves you getting pretty intimate with the fly-smattered windscreen.

That said, Deere reckons the eight speeds give enough overlap between ranges that you won't need to change under load anyway.

We found little reason to shift out of auto on haulage duties but when it came to running alongside the forager in BC range (where the box will auto-shift between the top two ranges), we found it kept shifting to C5 meaning the transmission had to rapidly downshift once in the new range to avoid a stall. In addition, when you back off the throttle it has a tendency to downshift fairly swiftly.

The answer? Run in manual in the field and auto on the road . It’s hardly a biggy – it just means your thumb gets a little more exercise through the day.

Likes

- Ultra-smooth shifting through eight powershift steps

- Drives like a CVT in auto mode – rarely any need to swap to manual

Gripes

- Delay between range changes – avoid shifting up when doing heavy draft work

- Settings screen not as intuitive as AutoQuad – cannot chose auto upshift point

Spec

- 24F x 24R semi-powershift

- 8-speed double-clutch powershift

- 3 powered range changes

How it works

When it comes to the inner workings of a tractor transmission, few things are simpler to get your head round than Deere’s AutoQuad box.

Short of a few electronic add-ons such as auto-shifting and speed-matching it’s the same set of cogs that was fitted into the first 6000-Series tractors.

Buried in its bowels are five mechanical gear ranges that are slotted into place using a manual stick shift on the right-hand console.

Splitting these up into useable chunks are four powershift stages. These use a set of hydraulic clutch packs and planetary gears which are controlled using a set of electronic buttons on the main gear lever. It’s a well-proven system and problems are pretty rare.

 John Deere AutoQuad

Setting it up

A fair chunk of the farming population will be pretty familiar with the basics of Deere’s Command Centre screen.

You can handpick the information you want to be displayed on the home screen, while tapping the transmission shortcut key takes you straight to the gearbox settings. Here you can tweak various options to get the best from the tractor’s set of cogs.

Thwack the Auto button at the top of the half black, half orange stick and the computer will take care of the shifts.

The point of the powershifts can be adjusted on an easy-to-use sliding scale. With Eco at one end and Power at the other, shuffling the arrow along the scale alters the gearbox’s characteristics. More power and the tractor will rev harder before upshifting – ideal for lugging around a heavy load.

Driving it

Anyone that has driven a John Deere tractor built in the past 20 years will be immediately familiar with the workings of the AutoQuad box.

Of course things have changed over time – the shuttle has moved from the right console to the left of the steering column and powershifting is done with buttons rather than a lever. Auto-shifting was added for the four powershift steps a while back and more recently a de-clutch button has joined the others on the main gear lever.

We love the box for its pure simplicity: select a cog, knock the shuttle forwards and you’re off. The four powershifts give plenty of overlap between ranges but whether having a thumb-clutch makes shifting up or down the gears any easier is debatable.

We just hope Deere doesn’t ditch the old favourite in favour of clever electronic jiggery pokery.

Likes

- Idiot-proof mechanical box

- Simple auto-shift set-up – sliding scale from Eco to Power

Gripes

- Less relaxing drive – fewer powershift steps

- No park lock on shuttle

Spec

- 20F x 20R

- 5 mechanical, manually-shifted ranges

- 4 powershift steps

- Clutchless shuttle

How it works

At the other end of the scale is the AutoPowr gearbox.

This is Deere’s ZF-built CVT transmission and like all the others on the market it uses a clever mix of hydrostatic and mechanical gearing to get you from A to B.

From the driver’s point of view it seems like there are no gears at all – just a smooth change of speed, a bit like hydrostatic drive on a combine.

But under the skin there’s a bit more to it. The two main parts of the box are pretty simple in their own right – there’s a mechanical part divided into four ranges on one side and a chunky hydrostatic motor on the other.

But the clever bit comes when these two drivelines come together. Both are fed into a set of planetary gears that – with a bit of help from the electronics – constantly vary the amount of hydrostatic and mechanical input that goes to the wheels. This gives you the impression there are no gears at all.

There is a penalty for all this slickness, though. Swash-plate oil pumps and motors are relatively inefficient at converting power into motion so you’ll find an AutoPowr tractor won’t be quite as perky as one of its AutoQuad equals.

At lower speeds within each imperceptible range, you get as much as 30% hydrostatic drive, but at the top whack it’s entirely mechanical.

 John Deere AutoPowr

Setting it up

Like Direct Drive, Deere’s version of a CVT is controlled using a stubby orange stick that can be slid up and down a doglegged channel.

The dogleg provides the first of two set points (the second is at the far end of the slider). These, named F1 and F2, effectively work as quick access cruise speeds that can be adjusted on the move.

Like with Direct Drive, operators can leave the tractor in auto mode or customise the settings (although it will adjust the ratio rather than downshifting). Both of these control engine rpm and transmission ratio together, but the two can be controlled separately in manual and pedal mode.

Driving it

We think Deere’s CVT set-up is the simplest to operate out of everything on the market. We particularly like the simple-to-fathom stick running in its two notch slot. The thumbwheel makes fine-tuning a doddle and, unlike other makes’ nudge-it-and-hope joysticks, you know exactly where you are with it because it stays put where you leave it in the slot. Orange micro-LEDs around the inside of the speedo confirm where you’ve got it set too.

In fact, it’s got to be the most straightforward box to get to grips with out of any. A brighter-than-average spaniel would have it figured out in minutes – knock the shuttle out of park and into gear, ram the stick forward and a gentle dab of right boot gets things moving.

Pull back on the stick and you limit your travel speed and increase the sensitivity of the throttle pedal. There is also the option of driving in manual mode where revs are control by the hand or foot throttle and the transmission on the stick.

A recent software upgrade also means AutoPowr boxes can have Fendt TMS-style pedal mode – engine rpm remains set for rev-dependent work such as mowing and the driver’s boot varies the speed.

Likes

- Most relaxing drive

- Ultra-simple slider sets forward speed range – thumbwheel makes fine-tuning a doddle

Gripes

- Settings screen not as intuitive as AutoQuad

- Less lively to pull away at junctions

Spec

- Stepless ZF continuously variable transmission

- Combined hydrostatic/mechanical drive


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