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af called it "the start of a new era" when

25th May 2000, Page 27
25th May 2000
Page 27
Page 31
Page 27, 25th May 2000 — af called it "the start of a new era" when
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it introduced the 95 XF back in 1997. From that you might have expected to see a completely new truck, but in the truck business this would be a rare commodity indeed. Instead, we got more of the same, only better. It's the cab that impresses most when operators look at the truck for the first time—which is as it should be. With the XF there were two options: the big Space Cab, with coil rubber suspension, and the even taller Super Space Cab, with 365mm of extra headroom and additional stowage, all riding on four-point air suspension.

Outwardly it looked very similar to the earlier 95 models, but with longer doors endosing the steps and giving a smoother profile. The interior got a complete makeover that included seats, dash, trim, ventilation and a bigger, elevated bunk.

Engine capacity was increased from 11.6 litres to 12.58 litres by increasing the stroke; the new block was stiffened to take the extra loadings. The 24-valve head with centralised injectors came in two parts, and a strong point for many operators was that this Euro-2 engine producing 43ohp and 48ohp came with mechanical injection.

Dry liners allowed tight piston liner tolerances that reduced the amount of oil blowby and particulates passing into the exhaust, but the downside was that it needed more effi8 dent cooling, which was supplied by a large radiator and a gear-driven cooling fan.

With Jacob's expertise Daf developed its '4 own engine brake, which is capable of delivering up to 29 okW of retardation at 2,400rpm. Early specifications included a 53ohp option in the form of the old N14 Cummins.

Last year heralded the end of mechanical injection. For Euro-3 much higher injection pressures are required, so for the I2.58-litre engine Daf adopted electronically controlled unit injectors developed by Bosch. For other manufacturers this has meant introducing an overhead cam, but Daf didn't want to add to the height of the engine or meet the cost involved.

Instead, the bank of unit injectors, which Daf has named UPEC (unit pump electronically controlled), is mounted rigidly at the side of the block, where a camshaft is driven via gear wheels from the crank. UPEC uses several parameters to control the tim ing of the fuel delivery and the duration of the injection, and Daf claims it has met the new emission standards over a wide range of operating conditions without having to increase fuel consumption.

Now, in addition to options of 43ohp and 48ohp, the 12.6-litre engine range boasts a 53ohp (39okW) XE 39oC rating. Although all are based on the 24valve unit, the 53ohp engine uses a CGI (compact graphite iron) block that is 6o% stronger (and was developed for use by the Daf Fina Racing team). Although only about tokg lighter than other 12.58-litre variants, it is some 300kg lighter than the

14.0 litre Cummins engine it replaces, and is available only as a Euro-3 unit.

Understandably, the 53o uses a heavier crank with bigger bearings, and the conrods are a different shape. Other differences are a bigger cooling system and an oil injection passage in each of the 530's six pistons for extra cooling. To optimise engine breathing an Allied Signal turbocharger is used with an electronically controlled waste gate.

Ever stronger transmissions have been needed to deal with the increase in power and torque introduced over recent years, which in turn have led to heavier gear shift forces. On the i6-speed ZF gearbox Daf has taken pneu matic servo assistance as standard with the 95XF Super Space Cab, and as an option for Space Cab models. This is said to reduce the lever effort by up to 50%.

Apart from using an Ecosplit 16 S 221 overdrive box and a stronger 13-tonne singlereduction axle with a faster (3.73:1) final drive ratio, the 95XF 530 tractive unit has a similar specification to other power options, which includes rear air suspension as standard.

The Space Cab and Super Space Cabs are virtually unchanged. Drum brakes are fitted front and rear, but Daf says a new generation of disc brakes is on the way.

• by NI Brock

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