British automatic breaks through to low cost
Tom Shelley reports on state of the art in automatic transmissions for both conventional, hybrid and electric vehicles.
After 15 years' effort in developing and marketing its patented designs for automatic transmissions, Antonov has finally secured a deal with a Chinese company, Chongqing Landai Industry Co, in which the two companies have set up a 50:50 venture to build and operate a new factory that will initially produce 200,000 units per year. The gearbox to be made there is the TX-6, a six speed unit capable of smoothly delivering 175 Nm of torque. The design involves replacing the conventional torque converter with a wet multi-plate clutch. It uses two parallel shafts with three pairs of transfer gears, four epicyclic gear sets and various hydraulically actuated brakes and clutches. These lock the different gear combinations together to achieve the six gear ratios and reverse (with what Antonov chief operating officer Simon Roberts describes as 'direct drives') when epicyclic combinations are locked together in fourth, fifth and sixth gears. The complexity arises, because, as Roberts explains: "We focus each of our gear ratios to give the best efficiency." Despite the number of parts, it is less expensive to manufacture than more conventional automatic gearboxes. It is also shorter, being only 325mm long, as opposed to 380 to 480mm for a design based on more conventional design technology. The torque rating is expected to go higher with future design iterations, and the units weigh 78kg. A future variant is planned that will deliver 375Nm of torque. The gearbox has been tried and tested in a Volkswagen Golf, which has completed 75,000 km so far without failure. We took the opportunity to drive this vehicle on both urban and rural roads, and despite our best efforts, we were unable to make it produce either jerks or unpleasant noises. It has been given the ability to creep forward after stopping, since drivers of cars with automatic transmissions have come to expect this. So far, six demonstrator gearboxes, have been built in the UK and put into cars, out of an intended total of 10. Delivered cost in China is expected to be around €1,000, and it is to be used in cars such as those made by Lifan Motors, which sell for around €7,000. It has a 1.6 litre engine and a 155 Nm torque requirement, well within the capability of the current TF-6. It is expected that 17 million new cars will have been sold in China by the end of 2010, double the figure for 2007. One of the reasons for targeting the gearbox at the Chinese market is their cars have less sophisticated engine management systems. A particularly sophisticated engine management system and CANbus is required to allow the use of dual clutch transmissions (see Eureka, March 2009), the solution favoured by many European car designers. As the gearbox changes up, it is necessary to reduce the engine speed so that a gear change can be made quickly as well as smoothly. The TX-6 gets over this problem by temporarily absorbing the speed differences in its wet clutches. DCTs are also significantly more expensive to manufacture and could be expected to cost €1,400 to €1,600. Possible alternative strategies for automatic transmissions that approach or exceed the efficiencies of manual boxes include variable ratio belt drives, widely used in small garden tractors, snowmobiles and motor scooters. This system, first installed in the British designed and developed Clyno car in 1923, is still around, but is currently out of favour with most car makers ever since the 'Variomatic', which was introduced on DAF cars in The Netherlands in 1958 and was hated by most of its users (although it still has its devotees and enthusiasts). Then there is Torotrak, another British invention, dating back to the 1970s. It has found commercial applications, ranging from the Harrier jump jet and the F1 KERS – Kinetic Energy Recovery System, to ride on lawn mowers, but it has never found favour with mainstream car manufacturers, who have instead looked to better automatic gearboxes based on gears. Although the Antonov TF-6 is to be a made in China as a product for Chinese customers, quality is considered to be a paramount requirement and 20% to 25% of the components will be sourced in Europe, at least to begin with. In particular, hydraulic blocks which have to manufactured to 'high tolerances' are likely to be made in Germany. The fortunes of Antonov appear to have been greatly transformed since the appointment of Dr Jos Haag as executive chairman about 18 months ago. Apart from the China deal, whose licensing agreement, signed in February 2010 is worth €20m, the company has diversified into other products and consultancy. Projects such as the two speed supercharger have been abandoned as a 'solution to a problem that did not exist'. Antonov is now involved in the development and production of transmissions for luxury market hybrid and electric cars and also a gearbox that will allow military vehicles to run alternators at full speed, even when their engines are running at idle speeds, in order to power growing volumes of electrical and electronic systems. The company is, additionally 'in discussions with a US West Coast manufacturer of electric vehicles'. Antonov's Roberts is a strong believer in gearboxes for electrically-driven vehicles, pointing out that, in the LimoGreen project, spearheaded by Jaguar, first studies showed that if the car was to be driven directly by a single motor, the 900Nm torque requirement led to a need to supply it with up to 1200A. Inserting a three speed gearbox reduces the need for motor torque to 450 Nm and the current requirement to 400A to 500A. The solution of a smaller motor and gearbox is also lighter, less expensive and fits the space in a Jaguar normally occupied by the conventional transmission. Two gears would solve the problem, but Roberts said this involved 'too big a step'; because of possible jolts, inertias, and requirements for durability, at least three gears is better. He said that first prototypes for the next stage of the project would be built in December, to go into LimoGreen demonstrator cars in January 2011. The company is also expecting to produce gearbox-equipped motors that are 'likely to go into 100 buses to be used in a certain sporting event in 2012', and 'could be ready for series production in 2013'. The gearbox was described as being: "Effectively a three speed DCT, but launched with motor and clutch engaged." A transverse variant has also been designed. Design Pointers • Antonov's six speed transmission with dual shafts and its multiplicity of epicyclic gears is the ideal solution for a new generation of Chinese cars being better value for money than alternatives • Geared automatic transmissions with no torque converter are much more fuel efficient than those that have one • The company is firmly convinced that electrically driven vehicles perform better with more cost efficient transmissions if there is a gearbox between the motor and the wheels. Three speeds seems to be the preferred configuration at present