Reluctant to Trust an Automatic Gearbox for Towing? Diverse Applications
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SPECIAL: TOWING WITH AUTOMATICS An earlier pattern automatic companion was the pre-selector gearbox gear shift, with Sport and (the automatic’s predecessor), most This Mercedes-Benz sectioned drawing shows Winter mode buttons, plus the path of drive from the engine, at the left, to manually-selectable gears famously designed by Major W G Wilson, the propeller-shaft output on the right numbered at the bottom that has a pedal in the conventional clutch location which is prodded when the driver wants to engage the next pre-selected gear. These systems were surprisingly popular, with applications from racing cars to tanks, and endlessly fascinating to me as a child, when watching the driver on London Transport RT buses. Which brings us to fully-automatic transmission and the torque converter, basically a fluid flywheel with a third static element, the stator, added. Depending on the design, this may multiply engine torque by up to around 2½ times at low engine speeds for pulling away briskly, though this extra torque diminishes as speed increases. Like the pre-selector, planetary gear sets (central sun gear with planet gears running around it, all within an outer ring gear) transmit the drive. Locking the gears by way of brake bands or internal clutches provides a number of ratios (in the early days, usually three plus reverse). Precision-engineered valve blocks channel pump-pressurised fluid to a series of and sophisticated electronic control. The which then adds its own trademark. valves and actuators to initiate the latter takes such factors into account as As to the thorny question of reliability, gear-change functions. engine load and speed, throttle position, nothing is perfect. But, subjectively, there But perhaps the purest and most logical road speed and whether the vehicle is seem to be more complaints about worn design was Continuously Variable climbing or descending. Some systems clutches and failed dual-mass flywheels Transmission (CVT). It makes much sense analyse driving style and detect when a than auto gearbox problems. to have a constantly-variable ratio. That’s trailer is attached, adjusting the Some car makers remain cautious and what Leonardo da Vinci thought in 1490, transmission’s gear shifting accordingly. restrict the noseweights and/or towing as did various car/motorcycle makers 470 With six speeds now common limits of their automatic versions, so it’s years later, notably Holland’s Van Doorne (sometimes up to eight) along with always wise to check specifications Above: modern company, of DAF fame. Remember the mechanical lockup systems and economy automatic gear thoroughly before purchase. slogan? It referred to the simple gear modes, fuel consumption and performance selectors follow a For towing, an automatic can be a boon. selector: “Forward to go forward/back to can match or exceed that of a manual, largely standardised Many autos provide seamless gear changes pattern, as in the go back.” And so it did – when you least solo and towing. timber-clad Phaeton just when they’re needed, with more expected it, sometimes! There are now Greater manual control – via gearstick, sophisticated types giving anticipatory numerous varieties of CVT made for very steering paddle shifts etc – ironically arrived down changes when slowing, cornering or Reluctant to trust an automatic gearbox for towing? diverse applications. at a time when automated gear changing had on descents. They make pulling away on Let Clive White guide you through the selection process Perhaps this brief overview has already become so advanced it could probably be inclines a breeze, removing all the stress of suggested why the poor old ‘slushbox’ more proficient than the driver. The choice Below: a different slipping clutches and possible stalling, and ccording to The Caravan gearing that can be altered on the move. the challenge being to devise a means of retains its detractors (calling it slushbox to hold a gear during acceleration or for approach to an integrate so well with cruise control for Club’s Information But, of all the skills required to operate a automatically disengaging the engine’s drive doesn’t help, of course!). downhill retardation is still useful, though automatic –the dual- those long motorway stints. clutch gearbox – department, many motor vehicle, changing gear has arguably for the vehicle to remain stationary, pull- These solutions were clever but many autos will kickdown to a lower ratio or shown here is a VW So maybe now’s the time to put your members still enquire, caused drivers the greatest amount of away smoothly and, if required, to enable a complex. Mechanical complication equals change up even in manual mode. DSG unit (left) foot up and retire from shift work. ■ often rather tentatively, difficulty. Early cars employed unforgiving non-driven condition during gear changing. cost and weight, early automatics offered In addition to the conventional Awhether they can tow a substantial cone clutches, while so-called crash One solution, the centrifugal clutch, uses limited ratios and torque converters always automatic, various types of gearbox offer caravan with an automatic towcar. gearboxes were just that. There had to weights to control its operation, disengaging slipped to some degree, resulting in poorer automation – CVT and dual-clutch systems The short answer is yes – modern be an easier way. below a pre-set engine idle speed as well as performance and fuel consumption than a being prime examples, though their The controls you will automatic transmissions in most cases are Various solutions were contrived which being released during gear shifting by an manual gearbox. Regular maintenance was principle driving controls are largely typically find in a at least as capable as their manual took a number of directions. Developments electric switch in the manually-operated crucial while the extra loadings of towing standardised. modern automatic – this is a VW Golf equivalents for solo and towing duties. in manual gearbox technology produced the gear lever. BMC’s Manumatic was a could cause overheating and the death of Many transmissions are made by a Yet, even after the best part of a century disc-plate clutch, the constant-mesh well-known system in the ’50s, but the many an auto box. Expensive to buy, repair small number of specialist companies, of clutchless gear-change systems and gearbox, quieter helical-cut gears and basic principle survives today in a number or replace and sometimes unreliable – poor often working closely with their car- self-shifting gearboxes, suspicion about synchromesh, all of which have now been of (usually small) cars. reputations are long lived. manufacturer customers to fine-tune them remains. Why? To find out, we must refined to the point where it’s difficult not Alternatively, the fluid flywheel relied on But times change. The modern them. It’s not inconceivable, therefore, take a drive back into history. to change gears properly. oil directed through specially-shaped vanes automatic benefits from years of that, say, a VW DSG and a Ford Durashift To cope with varying operating Other ideas were to do away with the in a twin-element ‘turbine’ to progressively development, better design, improved are based around a similar gearbox, but conditions, automobiles need a form of clutch – or at least its manual operation – provide drive above idle speeds. Its usual materials and manufacturing techniques, tweaked especially for or by the car maker 88 www.caravanclub.co.uk June 2012 The Caravan Club Magazine 89.