oodbye gearboxe!
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Inaenious si
LEYLAND is developing a continuously variable transmission which the company claims may replace manual or automatic gearboxes in a wide variety of vehicles, reports GRAHAM MONTGOMER1E.
A prototype has been fitted to a Leyland National bus with user trials expected in 1986.
According to Leyland, the key to the CVT development has been the design of advanced microprocessor-based electronic control equipment.
In simple terms, a CVT has no distinct ratio steps as with a conventional manual gearbox nor does it compare with an automatic transmission which merely has the same steps but activated automatically. With the CVT the gear ratio is varied continuously, as the name suggests.
The Leyland CVT operates on the roller traction principle in contrast to the belt-drive system used on the Daf/Volvo small passenger-car.
The Leyland traction roller system comprises three main sections: the variator which is the part providing the infinitely. variable ratio; an epicyclic section to provide reverse, neutral and forward; and the controller.
The variator unit — the design principle of which can be traced back to 1899 — consists of sets. of co-axial input and output discs which face one another.
The faces of these discs are curved or, more technically, have semi-torroidal tracks and the power is transmitted between these discs by small rollers with their axes at right angles to the main shaft. If the input disc is turned clockwise then these rollers transmit the power to the output disc causing it to turn anti-clockwise.
The drive is transmitted by an elastohydrodynamic oil film where a "wedge" of oil is trapped between the disc/roller faces. It is subjected to enormous pressure, typically 150 ton/sqin which causes variations in the physical properties of the oil making it semi-plastic.
This oil film also separates totally the metal surfaces of the discs and the rollers thus preventing wear. The oil is better defined as a "tractive fluid" which is specially formulated and thus expensive. As it is not degraded by flash debris or by products of combustion, as with conventional lubricating oils, the fluid life should be high.
The edges of the rollers can move across the toroidal faces connecting inner edges with outer edges, and vice versa, in a continuously variable progression.
The method of moving the inter-disc rollers to vary the ratio is by steering them which involves a castor angle and thus the variator can only rotate in one direction.
Because of this and the fact that the variator is permanently connected to the engine, reverse and neutral had to be provided and this is where Leyland's experience with Self-Changing Gears comes in.
An epicyclic assembly is provided where the sun gear is driven by the variator and the planet carrier by the engine.
The entire transmission can thus operate in two phases; low engine, produced epicyclically is used for reverse and forward speeds up to the equivalent of second gear; and high regime, where the drive is taken directly from the variator input.
Incorporated in this epicyclic unit are annular clutches to hold the high or low regimes, with these clutches being equivalent to the brake bands in a conventional SCG box.
According to Leyland it was the design of the mini-computer for the control system which provided the breakthrough to enable the variator and epicycl units to be combined in a viab CVT.
The CVT has a power handlir capacity of around 375k (500bhp) in its present form ar it weighs 330kg (6.5cwt).
The development costs to dal are around 000,000, which ii eludes some support from
tiDepartment of Industry.
The CVT has implications fc the light van and passenger ci side as well and David Burnie', product engineering director c Leyland Bus, claimed that it is totally viable product for Lel, land Vehicles, let alone BL, t produce alone without the nee for cooperation with anothE manufacturer.
Mr Burnicle said that, by th end of 1984, vehicles will b operating "in anger" in produc tion trials with full market avai ability in 1986. lGOSLAV commercial vehicle snufacturers are displaying rearkable ingenuity in keeping' with Western European actices, despite the harshest economic restrictions making 'ports of even components technulogy extremely diffiIL reports PETER STONHAM. Importing complete vehicles r use in Yugoslavia is now next impossible, and the few reign-made models at the Bel'ade Motor Show, which med last weekend, were there ore more in hope than antici Great strides have been made the past few years by Yugow manufacturers in modern'sg and extending their product nges, with the aid of licensing co-operation agreements with both Western and Eastern European firms.
But even these are now under pressure as Yugoslavia clamps down on any trade deals without guaranteed foreign exchange.
Clinging on to such links are MAN, Mercedes and Magirus. Each has a partner in Yugoslavia who buys designs, components or ckd kits in exchange for supply of parts back to West Germany for incorporating into production there and for partnership in selling to third countries. Here, the Yugoslav links help the Western firms win a stake in developing countries.
Typical of the co-operation deals has been that between FFB and Mercedes. FFB has plants producing heavy lorries over eight tonnes (FAP), engines (Famos), buses, coaches and now trolleybuses (Sanas and TAZ). Some models are Mercedes licence-built but increasingly FFB is introducing its own types — some with striking similarity to those of its partner.
Indeed, there are now two types of lorry with the Mercedes new-look cab on offer — those with the Mercedes badge having at least some original German parts/engine and covered by Mercedes quality guarantees, and the cheaper indigenous products with licence-made engines.
Also watching its models supplanted is Magirus Deutz, linked with TAM. Though the Magirus 12-tonner is still assembled in Yugoslavia, the Maribor manufacturer had an impressive array of lorries from its own "New B programme" at Belgrade, including a prototype 22tonner 6x4, with new bus and coach designs also on show.
TAM could be the first to produce its own top-weight artic in Yugoslavia soon — an area up to now ceded to western European and Eastern bloc designs.
The only British commercial vehicle presence at Belgrade was from Land Rover, showing the established and new One Ten models, and Bedford which had two Blitz CFs there. The lat. ter served to remind doubters of the toughness of the Yugoslav market — the Bedford importer reported sales so far this year of just four vans.