here - Ashcroft Transmissions
Transcription
here - Ashcroft Transmissions
new defender automatic Change for the better Defender auto conversions have been around for years – but never like this. Ed Evans reports on a new Defender 2.4 with electronic auto transmission W PHOTOS: SIMON HIPPERSON ere in the thick of Luton’s traffic, skimming around three-lane roundabouts and powering away from traffic lights with the best of them. Inside the Defender’s cab, the atmosphere is relaxed but for the occasional surge of the torque converter as it spins the power from the tuned 2.4DCi engine through a superslick automatic gearbox. A 2007 Defender should have a sixspeed manual gearbox that has you stirring gears every few revs for the sake of reduced emission levels. But that gearbox is under the bench back at Ashcroft Transmissions’ workshop. In its place, we’re having great fun with the company’s latest conversion: a four-speed electronically controlled auto box that’s so smooth, you’ll forget there’s even a gearbox there. But this conversion is no simple component swap. It’s taken months of painstaking design engineering and the co-operation of specialist companies to mate the ZF automatic gearbox to the latest Defender’s Ford-derived engine. We’re long past the era of simple outand-in conversion jobs – the trick today is in orchestrating the engine and transmission electronically, and Ashcroft and its engineering colleagues have gone overboard to match these units and give the driver full control of how the gearbox will perform. In basic modes, this set-up has all the competency you’d expect in a Discovery 3: full auto, semi-auto ‘sport’ flick-shift and manual hold. But the Defender deals with extremes, and that demands an extreme transmission that’s fully programmable by its driver – a bespoke transmission with characteristics that can be altered at will. Set your own individual gearchange speeds; control the hydraulic pressure to set fast or gentle gearchanges; have the torque converter lock up when you want it to. It all adds up to a gearbox that can be programmed for optimum off-road performance, best towability, easiest town driving, sports acceleration or even the mood of the driver. All that, and you can watch it happening on the programmable control/display unit. And it gets better. Even the 2.4 4cyl Ford diesel has been tinkered with – or, Ë 28 LRO Spring 2008 Spring 2008 LRO 29 new defender automatic for normal run-out tolerance of 0.005-inch between engine and transmission. A new bellhousing (strictly, a torque converter housing) was designed to mate the ZF gearbox to the engine and house the torque converter. The complete drivetrain is assembled by fitting the flywheel, boss and flexplate to the engine, bolting the bellhousing to the gearbox and fitting the torque converter in the bellhousing, then offering the transmission to the engine. It’s a seamless arrangement that looks, from under the vehicle, like standard build. Compushift The Compushift is the input point for bespoke gearbox settings, allowing it to be customised to the driver’s needs This shot inside the auto box shows typical clutch pack of alternating friction and steel plates, which are clamped together when shifting gear This shows a clutch assembled in its drum. Clutch packs are operated by hydraulic pressure generated by the pump and then applied by valves rather, remapped by tuning specialist Superchips to best suit the gearbox electronics. That mod just happens to include another 99Nm torque and 38bhp over the standard (already high-performing) diesel. Most of us know the ZF4HP22EH gearbox, even if that name hardly trips off the tongue: it’s the standard auto unit from the Discovery 2. This unit is well proven and fairly bombproof, certainly capable of distributing a lot more load. But it’s the Compushift-derived electronic control that sets Ashcroft’s system apart. Before we get our heads around that, it’s worth recapping briefly on how an auto box works. Automatic transmission The engine drives a torque converter, which drives the gearbox. Turbine blades and impellers in the fluid-filled torque converter 00 LRO Xxxxxx 0000 Dave Ashcroft displays the friction and steel discs of a clutch pack taken from a Tdi – typically burnt out by either wear and tear or excess heat amplify engine torque at low engine speeds until the engine develops more power. The converter then ‘locks up’ and acts as a fluid flywheel transmitting the drive directly (and more efficiently) from engine to gearbox. For rapid acceleration, a ‘kickdown’, which is operated by fuller movement of the accelerator pedal, quickly selects a lower gear. Gears are selected and deselected by multi-plate friction clutches clamped together by hydraulic pressure during gearchanges. The torque converter is locked up and released by a similar clutch pack. Failure to achieve torque converter lock-up speed for prolonged periods, such as when towing or climbing, can cause overheating that, in turn, can cause clutches to burn out. Ashcroft’s system avoids these issues by programming the gearbox to suit the loads and driving conditions. This is the automatic gearbox’s oil pump, which pressurises the fluid in the gearbox to operate the gearchange clutches hydraulically hardware development Unlike Ashcroft’s earlier Td5 auto conversion, the new Ford engine had never been mated to a suitable automatic gearbox. To develop a prototype, Ashcroft bought a Ford engine and cut it in half to install it on measuring equipment. You’ll see this halfengine in our mock-up pictures. Ashcroft’s conversions are designed to retain as much of the vehicle’s factory specification as possible. That meant the new auto box must be developed as a ‘drop-in’ unit: a direct replacement for the manual box. This ensures the rest of the vehicle remains unaffected, including the transfer box position, which, on the latest Defender, is angled over an additional 10º. A boss was designed to fit the 2.4 crank and carry a flexplate that holds the new torque converter. The flexplate compensates The Compushift electronic control is the brain in charge of the ZF auto box. It’s also the input point for those bespoke gearbox settings, allowing the transmission to be customised to the driver’s needs. Compushift has three menu levels, so there’s no need to be a genius to adjust the settings. Simply select the level that’s comfortable for your own understanding, or ask Ashcroft to programme it for you. The Compushift system has long been around in the US, handling brutal torque from drag racers and muscle cars. Ashcroft worked with its manufacturer, HGM in California, to adapt the logic to the Defender. Maddison 4x4 in North Yorkshire (www.maddison4x4.com) had already worked with HGM on its own Td5 auto conversion, and assisted Ashcroft in submitting the ZF auto-box data for a new system to be developed. The Compushift system has four basic settings, each easily selected by the driver: 1. Automatic – conventional auto with normal facility to hold individual gears, subject to safety override; 2. Auto with switch shift – fully automatic plus the option of using a rocker switch for manual up/down gearchanges; 3. Auto with towing mode – an additional switch raises gearchange pressure and speeds to values preset by the driver, so the box delays the upchanges, spending longer in lower gears. The torque converter stays locked up until the driver shifts down to third, improving downhill engine braking; 4. Manual –overrides the ECU for competition use where full driver control is needed. The system is not overridden to prevent over-revving the engine, so the driver must change gear at the necessary times, as with a standard manual. If the vehicle is towing hard at 50mph and lock-up speed is 55mph (which is the Range Rover Classic’s speed), the oil will eventually overheat. Conventional automatics have a fixed lock-up speed that can be changed only by modifying the hardware inside the unit, but Ashcroft’s system can be programmed to lock up at, say, 48mph – giving efficient, economical towing with no risk of overheating the fluid. It’s programmable to any reasonable cruising speed. Ashcroft designed this bespoke torque converter housing (bellhousing) to mate the ZF gearbox to the 2.4-litre engine Housing bolts directly to auto’s existing mounting holes. Square cover gives access to bolt the torque converter to the engine Torque converter fitted inside housing, engaging its output shafts with the gearbox input and oil pump drives Torque converter is well inside housing, leaving room for the new engine adapter boss and flexplate That’s the auto box, new bellhousing and torque converter assembled – now for the engine fittings In this mockup (using the 2.4 halfengine), a new adapter boss is bolted to the engine’s flywheel and crankshaft… …followed by a flexplate bolted on to the crankshaft boss and driven by it. The flexplate compensates for run-out Automatic transmission is then fitted and bolted to engine. Torque converter is bolted to flexplate via bellhousing access hole Compushift display and controller The in-cab display/control unit allows the driver to customise the gearchange points in respect to accelerator position, the firmness and speed of gearchanges and the torque converter lock-up speed. Rudimentary shift speed adjustments can also be made using screws on the side of the electronic control unit (ECU). When installed in the vehicle, the automatic gearbox and torque converter housing blend into the typical Defender underside The display gives a live read-out of the gearbox conditions. Tab through the menus to see the following: l Selected gear; l Gearbox mode –auto, auto/switch-shift, auto/towing mode, manual; l Gearbox oil temperature; l Shift speed adjust – raises or lowers gearchange points (the road speeds at which the gears change) as a group or individually; Dave Ashcroft explains his choice of torque converter for the new system. Auto gearbox with converter housing stands behind Spring 2008 LRO 31 Ë new defender automatic I’m a fan of autos for off-roading and would have liked to plunge Ashcroft’s only auto demonstrator into some serious mud. But with no support vehicle, no winch and no one else around, Dave was understandably keen that I didn’t sink his investment. Anyone who’s been here will know that the surface consists of clay mixed with Evo-Stik, which instantly transformed the road tyres into larger-diameter slicks. The traction control should deal with that – and it did. Steep, rutted climbs and descents on mud that has the adhesion of cooking fat made no difference to the 90 as its wheels locked and released under traction control, with the auto transmission taking the whole deal quietly in its stride. The transmission worked well in full auto, manual hold and switch-shift modes, with both high and low range on the transfer box. Engine braking was good in switch-shift bottom gear low-range although, when releasing the throttle, there’s a momentary l Pressure adjust – raises or lowers the hydraulic pressure activating the clutch packs. Raising the pressure causes the clutches to clamp harder, giving a faster gearchange – useful for heavy towing to avoid slipping or burning the clutches. Lowering the pressure gives a smoother, slower change; l Hydraulic pressure can also be raised for low-range and reverse gears to give accurate driving control; l TCC – Torque Converter Clutch can be set to lock-up and unlock at desired road speeds. To increase longevity and prevent damage, the TCC will not lock-up above 65 per cent throttle; l Downshift offset –adjusts kickdown sensitivity. The higher the offset, the more readily the box changes down when the accelerator is pressed; l Diagnostics mode – for electronically displayed troubleshooting. Engine upgrade Standard ECU maps have an anti-stall function that depends on sensing a steady, solid drive from engine to transmission via the manual’s conventional clutch. So the Defender’s ECU needed modification to accept the varying torque transmitted from the auto box’s torque convertor. This, plus the engine performance upgrade, took three months of development. Inside the cab The auto gearlever is mounted in a new injection-moulded console that matches the colour and texture of the existing trim. The auto lever is nicely positioned where your hand naturally drops on to it from the steering wheel, though it slightly restricts access to the hi/lo and diff lock lever until you’re used to it. Compushift from top clockwise: wiring for petrol/diesel engines, essential bling stickers, display/ programmer, ECU, instructions The ‘CommandShift’ in luxury Land Rovers, which allows gearchanging by a simple push forward or back on the gearlever, is replicated here by a rocker switch mounted flat on the console – rock forward to change up, back to change down. Ashcroft has designed useful extras into the robust console. There’s a mobile phone recess with grip mat, and a top recess for oddments. The rear incorporates a sturdy cubby box with a lockable lid that folds back flat to form twin cup holders. On the road An automatic should come into its own in town driving. Leaving Ashcroft’s works to hack through the Luton traffic provided the ideal test, and it took little time to get used The stand-alone Compushift electronic control unit (housed under the console) computes driver input to control the automatic gearbox selection parameters The ECU sends out its control signals via this pin-pack on the gearbox to the electro-hydraulic valves operating gearchange and torque converter 32 LRO Spring 2008 Mock-up: half-engine, with boss, flexplate, torque converter and the torque converter housing/auto box (flywheel excluded for clarity) Oil temperature sensor in auto box oil sump tells ECU to vary gearshift pressures with the viscosity of oil ECU gets signals from gear position switch, and from accelerator pedal throttle position sensor All parameters can be adjusted and monitored by this Compushift controller and display unit, which can be mounted in the cab to this auto box. In traffic queues the auto’s creep speed is gentle and controllable, and drive engagement is imperceptible. Take-off, as traffic moves away, is smooth, progressive and rapid. There’s the usual revviness when working on and off the throttle as the torque converter spins up and down, but its not intrusive, and gives a useful, audible indication of exactly what’s going on down below – in a modern Range Rover you’d hardly hear this and hardly care anyway but, in a working Defender, you need to know what the driveline is doing. Brush away the town traffic and the Defender settles out on the open road with the torque converter locked up into relative silence after 55mph. It was only after the Defender stopped changing gear that I realised I hadn’t even felt the gearchanges – it really is that smooth. To my mind, that puts this system alongside the best contemporary autos. On kickdown, there’s a satisfying roar from the engine and torque converter, justified by a respectable gallop that has the Defender overtaking 60mph traffic briskly. On the way back into Luton there was time to play with the auto’s switch-shift, using the rocker switch mounted alongside the main selector lever. Press forward to change up, backwards to change down. In this mode the gearchange is sharper (it’s adjustable) but still smooth. As a way of controlling the gears manually it’s more convenient than using manual select on the main lever, and handier than the relatively cumbersome CommandShift on non-utility Land Rovers. To revert to full auto, the main selector lever has to be moved to third gear and back to drive, which feels a tad clumsy. Ashcroft expects to rectify this soon with a new-generation ECU. Off-road test That wasn’t just an out-and-back trip. We’d been to the Devil’s Pit off-road centre at Barton-le-Clay (www.devilspit.co.uk). Console houses conventional auto gear selector and rocker switch-shift. Phone recess and grip mat to right of hi/lo lever, oddments tray at rear of console Armrest opens up to reveal lockable cubby box whose lid folds back flat, giving twin cupholders and sandwich platform – neat, user-friendly touch delay before the engine revs come down. That feature has to be factored in when approaching severe descents. Otherwise, it’s so controllable and slick off-road that there’s a tendency to forget it’s an automatic and simply concentrate on what the wheels are doing, where they are, and where you’re driving – and that’s just how it should be. No mpg figures are available yet, and our test run wasn’t long enough to give an impression. But given the minimal effect the auto box has on Discovery 2, the relative economy of the 2.4 engine, and the fact that a chipped engine doesn’t necessarily need to be thirsty, running costs could be close to those of the standard manual version. If so, it’s the ultimate auto Defender. Getting converted Conversion of the new Defender 2.4 to automatic at Ashcroft’s works costs £5816 and takes two weeks. Book a test drive in its 90 XS auto to try it for yourself. The company expects to offer the conversion in kit form in the near future. Ashcroft still converts Td5 models to automatic – and they are now also available with Compushift. Contact Ashcroft Transmissions, Units 5 & 6, Stadium Estate, Cradock Road, Luton LU4 0JF: www.ashcroft-transmissions.co.uk, 01582 496040. Ë Xxxxxx 0000 LRO 0