Slowing down Swedish style
Page 11
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EXCLUSIVE • Six months ago Scania unveiled its integral retarder for PCVs at the Rai Bus Show. The hydrodynamic secondary brake is now available on trucks too: it will be offered as a UK option on 14-litre vee-eights from May and on 11-litre straight-sixes from October.
CM covered the system in a recent Engineer's Notebook (CM 4-10 Feb); since then we have been over to Sweden to drive a retarder-equipped Scania.
Our test truck was a three-axle R143-470 rigid running at 24 tonnes and fitted with the latest GRS900 14-speed range-change and splitter box. Not the most obvious choice for a retarder test, but with a power-to-weight ratio of 14.6kW/tonne(19.8hp/ton) it needed some stopping.
The test route was an icy, snow-swept back road near Scania's Sodertalje factory which demanded plenty of care, particularly when braking for sharp downhill bends.
The retarder can be operated in two ways: via a dash-mounted control lever, or the foot brake. The dash lever provides increasing levels of retardation with the final position bringing in the exhaust brake. Alternatively the first touch on the brake pedal activates the retarder; the main service brakes follow when greater pressure is applied.
Hand control The hand control lever is always connected but the footbrake mode can be disengaged by a simple onoff switch on the dash.
Both methods incorporate a downhill speed control. With the hand control the driver simply uses the lever to gain the required retardation, then holds it by pressing a button on the end of the stalk. Using the footbrake/retarder combination the driver slows the vehicle down to a comfortable speed. When he releases the brake pedal the computer controlled retarder maintains that speed, bringing in the exhaust brake for extra stopping power as and when it's needed.
Either way the service brakes are fresh when you need them. The retarder also allows quicker, and more controlled downhill descents so average journey times can be improved over hilly terrain.
During our test drive we tended to use the hand control when approaching junctions or hazards, just to wash off the vehicle speed before releasing the retarder and continuing on our way. On downhill runs with tight bends to negotiate it was easier to use the footbrake to set the retarder, leaving both hands free to turn the steering wheel, then "topping-up" with the service brakes when needed.
Despite the treacherous road surface we were left with a tremendous feeling of security, being able to slow down the truck rapidly on the retarder without any hint of skidding or sliding. Even when the clutch is dipped to make a full or split gear change going downhill the retarder continues to provide full braking effort.
Unlike a conventional exhaust brake or a Jake Brake the Scania integral retarder is very quiet; the only time you really hear it working is on the third or fourth stage of the hand control when the exhaust brake is activated.
After a spell behind the wheel we handed over to Christer Hellberg, Scania's regular press demonstration driver. After our cautious approach it was interesting to see how quickly the R143470 could be taken downhill and around tight slippery bends while still retaining complete control. On all but the tightest bends Hellberg was able to check speed by the retarder alone.
Normal operation Under normal operation the retarder works in conjunction with the truck's ABS; in the event of a fault it is automatically disconnected and the problem is signalled by a flashing diagnostic code unit in the dash.
After only a short time with the Scania retarder we are convinced of the benefits it can provide in terms of safety, quicker journey times and reduced service brake use. Being an integrated factory. fitted product, backed by Scania warranty and serviceable by Scania dealers, will strengthen an already impressive sales story.
Scania (Great Britain) has yet to come up with a price for the retarder, but according to product marketing manager David Burke it will be competitive. After announcing that it would only be offered on 4x2 tractors due to "packaging problems", Scania has decided that it can be ordered on any twin-steer with a front mounted or vertical exhaust.
by Brian Weatherley