Torotrak pioneers traction fluid R&D rig

A company developing traction drive infinitely variable transmissions (IVT) has developed what it claims is the world’s only traction fluid testing rig.

Even the most innovative traction drive transmission for passenger car and commercial road vehicle application is effectively useless – a laboratory toy – without a “perfect” traction fluid to ensure top-class performance and long-term durability.

Traction fluids are characterised by their coefficient of traction – the ratio of transmitted force to contact force. The molecular structure of these synthetic fluids is highly complex, and the formulation a closely guarded secret.

The fluids have highly intricate three-dimensional structures to bring the molecules together to retain very high friction. Developing these fluids has required complex computer programs and agile minds.

Year on year, advanced formulations have been created to push forward not only the boundaries of transmission performance but the levels of understanding under a highly secretive cloak of closely guarded knowledge.

It is as much in the interest of the fluid makers as well as the transmission designers that the “best” fluid is evolved. Hence Torotrak’s bespoke traction fluid test rig which has beeen designed and developed by the company to test traction fluids "at much higher contact pressures, temperates and speeds" and "under realistic contact conditions".

Why are these fluids so vital to these transmissions? In a traction drive transmission, the flow of power and torque varies seamlessly through varying speeds from full reverse through zero to full forward requires mating surfaces of tough, high-strength steel materials.

Traction fluids are required therefore to prevent seizure and abrasion if the transmission if to offer the user – be it the user of a passenger car, bus or, in the most demanding environment of all, heavy commercial vehicles and high duty off-road construction machinery – long, and maintenance-free life.

In the case of the Torotrak IVT, where rollers and discs (the toroidal chamber) come into contact with one another, that these fluids play a vital role in making sure the two surfaces do not in the normal sense of the word “make contact”.

It is the movement of roller within the disc that creates the infinitely variable ratio change. Disc and roller must not touch but must transmit torque (power) through surface tension.

These highly specialised elastohydrodynamic fluids are necessary – vital – in traction drive transmissions where they provide the high shear film strength that allows the transmission to transmit torque.  But other factors play also their part such as load-carrying capacity; wear has to be a minimum, and the fluids must endure high temperatures for long periods of time. The fluids must also remain stable and not undergo formulation decay.

The secret and iterative formulations that have been developed over years have required fluid makers to explore a wide range of additives to obtain the levels of performance – itself a moving target as potential transmission makers set about putting their transmissions on the market.  

And so it is that Torotrak, based in Leyland, Lancashire, has developed its own specialist testing rig to help in the development of these fluids but also to progress its own transmission designs of one kind or another.

Torotrak is therefore understandably proud of the work it has done in helping to develop an understanding of elastohydrodynamic traction fluids that frankly are vital to any successful IVT or CVT – continuously variable transmission.

Torotrak claims its traction fluid testing rig is the only one of its kind in the world. Developed by Torotrak it is used to thoroughly investigate the properties of traction fluids. Such investigations allow traction fluid makers to further enhance their fluids.

So while traction fluid suppliers have their own rigs for the continuous development of their materials, the Torotrak rig provides a “real life” environment in which the fluids can operate. Fluid suppliers can therefore feed results into their own simulation software and if necessary “tweak” their materials further directly as a result of work at Leyland.

Torotrak claims all the major traction fluid suppliers test their fluids on this rig over a range of operating conditions, most notably at high contact pressures and shear stresses, at high fluid and material temperatures, and at various operating speeds.

According to Torotrak’s Dr. Adrian Lee, who has spent many years helping to develop IVTs, the company’s engineers are obtaining “excellent results”.

Most notably, the rig is used to assess how fluid properties are affected under realistic contact conditions in the variator.

Among suppliers of such elastohydrodynamic fluids are Monsanto Company with its Santotrac 32, 50, 70, 332FG, 1842B and MCS-2080A fluids. Idemitsu Kosan Company in Japan is another supplier of these fluids and so too is Shell.

Significantly, perhaps, it is through the Chinese walls that are thrown up around various transmission innovators and materials and fluid suppliers that snippets of information could  ‘migrate’ from one company to another regarding the effectiveness or otherwise of a particular design or engineering feature

Interestingly, Torotrak on its web page under the heading "Driving change" the company highlights its new traction drive fluid laboratory. Following a short video of the lab., Torotrak highlights the work of other CVT and IVT innovators based on YouTube video clips including: one from Fallbrook Technologies Inc. entitled an "Introduction to NuVinci CVP"; another "How a CVT works" by Team Industries Inc. and finally introduction to the D-Drive IVT. 

                                         Tortuous

The road to putting a viable, durable continuously variable transmission on the road in large numbers is long and tortuous, as witnessed by Torotrak plc over the past 25 years during which time it has accumulated a large number of patents.

Indeed, it is over 27 years ago that the entire Rover Group’s CVT engineering team became part of the British Technology Group (BTG), itself spun out of the UK Government’s National Research Development Corporation (NRDC).

However, work on CVTs had been well under way before then both at BL Technology Ltd in Gaydon, Warwickshire, and by individuals including Forbes Perry with his company Perbury Engineering Ltd.

At that time BTG (1987) acquired all of the CVT intellectual rights belonging to Rover Group (cars), Leyland Vehicles (trucks and buses) and Lucas Aerospace (aerospace applications, like the Harrier ‘jump jet’).

A year later, in 1988, BTG formed Torotrak plc, but it was not until some five years later that Ford Motor Company announced formally that it had begun working with Torotrak, helping to fund a £2 million programme to produce a pre-production unit for fitment in Mondeo passenger cars.

In 1994, Ford became Torotrak’s first major licensee and in 1995 Torotrak signed other license agreements, including those with Toyota in Japan and FFD-Ricardo (FFD being formerly Ferguson Research) in the UK.

In 1997, Torotrak’s CVT was incorporated into a small fleet of Ford Mondeo passenger cars and Toyota took delivery of its first unit.

Believing the future for CVTs looked rewarding, BTG demerged Torotrak into a stand-alone business unit in 1998 and floated it on the London Stock Exchange to raise £50 million.

Following on from that, Ford extended its interest in the company’s transmission to the point that it equipped at least 15 5.4-litre Expedition sports utility vehicles (SUVs) with the Torotrak IVT before eventually deciding that that particular design of CVT was not suitable for its vehicles. Presumably, Ford could not make a business case to put the UK design of transmission into production. Investment in conventional (geared) automatic transmissions was already substantial.

Ford however was able to make a business case for a push-belt CVT for small cars of the type invented initially by Van Doorne in Holland and used in the DAF 25 and 33 models, and further developed by Volvo.

For this push-belt transmission, Ford used its transmission plant in Batavia, Ohio, which started life in 1980 producing front-wheel drive transmissions, including the ATX and the CD4E.

In 1999, Ford partnered with German transmission maker ZF (which held 51 percent) to revitalise the Batavia plant. CVT production began in late 2003 but two years later Ford purchased ZF’s stake and owned the plant outright to make the CFT23 and the CFT30 CVTs from 2005 through to 2007. Both were belt-drive CVTs. Ford shuttered the plant in 2008.

Meanwhile at Torotrak, others showed great interest in the transmission including General Motors which tested the design and seemingly approved it but was not prepared (like Ford) to manufacture the unit itself.

Nissan on the other hand went further and developed its own type of toroidal transmission. Indeed, Nissan in Japan became one of the pioneers of production CVTs. In 1992 the company introduced CVTs (the Fuji Industries ECVT) into its March passenger car and in 1997 announced what it called the world’s first Hyper CVT for front-wheel drive cars.  Both of these CVTs operated on the push-belt system.

In 1999, Nissan launched its own toroidal transmission called the Extroid for rear-wheel drive cars of around 3-litre engine capacity.  The Extroid had two variators, each with a set of discs and rollers.

But, possibly in an admission that its toroidal design could be improved upon, the company announced in 2003 the arrival of Xtronic, “the next generation” CVT suitable for cars of 2.5- to 3-litre engine capacity. Xtronic uses a steel belt and pulleys to effect ratio change.

Nissan fitted the Xtronic to the Altima in 2013 claiming “quiet, seamless performance” from a transmission that offered a “40 per cent reduction in friction” and a “15 per cent fuel economy gain”.

Mazda, part owned by Ford Motor Company, also ventured into toroidal CVTs with a design which dispensed with the torque converter (linking engine to transmission), replacing it with a geared neutral start.

The CVT and the IVT have inevitably proved to be a happy hunting ground in terms of developing patents to protect design ideas and with a view to exploiting these ideas financially in the future.

In the 10 years from 1988 to 2008 many names have appeared in UK patents in connection with toroidal CVT/IVT, most notably those of Tom Fellows, Chris Greenwood and Geoff Soar. The first of these to lodge a patent may have been Tom Fellows in July 1988. But there have been other names.

Sometimes, CVT designs have not been patented. For to patent is to reveal; and some engineers have not wished to reveal their designs for the wider world to see and maybe ‘copy’.

So the journey for the CVT and the IVT at Torotrak has been a long one and it is by no means complete as the British company’s most recent link with Flybrid Automotive Ltd of Silverstone testifies.

Today, Torotrak’s thrust is in three main areas: IVTs for main drive transmissions in off-highway vehicles and heavy commercials with a view to improving fuel economy by 20 per cent; M-KERS – mechanical kinetic energy recovery systems for buses, trucks and passenger cars aimed at improving fuel economy by up to 25 per cent, and V-Charge – a variable supercharger that allows airflow and boost pressure to be managed independently of engine speed. Flybrid’s input is directly linked to M-KERs. The most high profile name with which Torotrak’s technology has been linked is that of Allison Transmissions of the US which produces transmissions for heavy commercial vehicles.∎