A novel speed variator designed, engineered and developed by a Lancashire firm is among a number of novel continuously variable transmissions bringing CVT advantages to smaller tractors.Torotrak’s IVT variator, which has been selected by driveline manufacturer Carraro DriveTech for future products, is likely to be seen in a commercial tractor within the next two years.

It will join the SuperSpeed CVT, a novel chain and pulley variator transmission developed by another off-highway drivelines specialist Oerlikon Graziano in partnership with CNH Global and the slimline hydro-mechanical designs developed by Same Deutz-Fahr and Agco’s Fendt arm for orchard and small field tractors.

These new designs are all different but have been conceived to bring the easy driving characteristics, smooth and precise speed control and power efficiency potential of big CVT tractors to machines about the 100hp mark and less. Mostly, they will be installed in tractors used on stock farms and in orchards and vineyards, as well as for commercial groundscare work.

The size and layout of the hardware is therefore critical to allow installation in tractors small in stature and – for vineyard and orchard use – narrow in width.

The Agritalia division of the Carraro Group builds specialist tractors for sale under its own name for the Agco, Claas and Deere using transmissions from the DriveTech division.

Carraro DriveTech selected the Torotrak IVT variator after a lengthy evaluation programme. Unlike familiar CVTs, which use a hydraulic pump and one or two hydraulic motors to provide speed variation within a given mechanical ratio, this is a mechanical device that positions two slim rollers between two concave-faced discs.

One disc transmits drive from the engine, the other sends it out to the wheels. As the rollers that connect the discs change angle in response to torque load or control input, so the output speed relative to the input speed is infinitely adjusted.

It’s a very simple device with few moving parts and there is no metal-to-metal contact because a thin layer of traction fluid provides the interface between the discs and rollers.

It can be controlled using simple mechanical or more sophisticated electronic controls and Torotrak says the technology is fully scalable – so although its first agricultural application will be in small tractors of no more than 100hp, it can be scaled up to drive much larger machines.

Carraro DriveTech – the Italian manufacturer that builds many of the front drive axles seen on farm tractors – has incorporated the Torotrak IVT variator into its new VaryT transaxle family comprising units for up to 60hp, 90hp, 100hp and 150hp.

According to Pierluca Sartorello, product marketing director, the Torotrak unit has come through the company’s most exhaustive testing and development project with flying colours.

“It is one of the simplest, most efficient and easiest to control systems available,” he says. “It uses only one-third of the parts employed in other power-split CVTs and has definitively better efficiency resulting from its all-mechanical structure.”

The Torotrak IVT’s lack of maintenance needs and reliability under testing are such that it will be installed in the VaryT transaxle assemblies as a sealed unit.

“The transmission is likely to be introduced in a customer’s new small tractor range within the next two or three years,” adds Mr Sartorello. “But our technology licence allows us to apply the system in tractors up to 160hp.”

The new Chain Continuously Variable Transmission (CCVT) stepless transmission developed by Oerlikon Graziano and CNH Global also has an all-mechanical variator – this time employing a chain running around two variable diameter pulleys.

Unlike the belt and pulley transmission used in the DAF Variomatic car of the 1970s or the more recent chain and pulley designs used in some Ford and Audi models, the CCVT does not transmit the engine’s full power and torque; it is mainly used for speed variation.

The SuperSpeed transmission used in New Holland Boomer 3000 EasyDrive tractors has a chain and twin pulley variator mainly providing speed variation.

“Power fed through an electro hydraulic forward/reverse clutch goes directly to the sun gear of an epicyclic set and also to the chain and pulley variator,” explains Rupert Boobbyer of New Holland. “The variator is connected to the planet carrier of the epicyclic assembly, with output to the wheels coming from the ring gear.”

Chain slippage is eliminated by the hydraulic pressure that clamps the chromium steel pulleys and there is a torque sensor to activate the drive clutch if necessary to prevent the engine stalling.

“That means you can get plenty of push with a loader into a heap of soil without having to worry about the engine,” says Mr Boobbyer. “Using cruise control, the drive ratio is automatically adjusted if an increasing draft load drags the engine below a pre-set minimum speed.”

The Oerlikon Graziano CCVT is already being used in the three 41-51hp compact tractors that make up the New Holland Boomer 3000 series used mainly for commercial groundscare work.

In future, an uprated version of the single-range CCVT will be installed in new range of general purpose agricultural tractors from CNH spanning 85-115hp – and in tractors from other Oerlikon Graziano customers.

The Deutz-Fahr Agrofarm 430 TTV (pictured) and similar Same Silver3 Continuo 100 and 110 use an in-line stepless hydro-mechanical transmission.

Same Deutz-Fahr’s first in-house CVT is more conventional than the Torotrak/VaryT and CCVT mechanical designs in that it combines hydrostatic and mechanical drives like as used in full-scale farm tractors.

Its innovative feature is in the way the components are arranged in-line to keep the assembly narrow enough to be installed in small field and narrow fruit tractors.

A variable displacement pump and a fixed displacement motor form the hydrostatic unit at the front of the installation, providing speed variation and a varying proportion of total drive.

This assembly’s output is channelled – along with drive from the engine – through an epicyclic torque splitter giving a variable proportion of mechanical and hydraulic drive. The transmission is completed by a clutch to select one of two forward speeds – work zero to 19kph for work, 19-50kph for transport – and a reversing unit.

“To make starting the engine as easy as possible it is decoupled from the transmission by a hydraulic clutch,” notes Angelo Ripamonti of SDF. “The same mechanism is used to eliminate drag when the tractor is stationary but powering a pto-driven implement and the clutch can also disengage drive to the wheels during emergency braking.”

The new transmission has been launched in the 99hp and 109hp Same Silver3 Continuo 100 and 110 and equivalent Deutz-Fahr Agrofarm 420 TTV and 430 TTV models.

Fendt engineers also conjured up a component remix when they devised a stepless transmission to suit the 70-110hp range of Fendt 200 Vario field and vineyard/orchard tractors.

The ML70 unit exploits the Vario’s use of wide-angle hydraulic pump and motor for drive and speed variation by installing some components in the rear axle.

Apart from helping to minimise overall width, this solution means the new tractors not only have the compact overall dimensions they need but also the unique advantage among orchard/vineyard tractors of a flat floor cab.

As with the transmission in the Fendt 300 Vario tractors, the ML70 has a single mechanical range and a planetary gear set that progressively blends mechanical and hydraulic drive from 100% hydraulic to 100% mechanical drive at maximum speed.