A Combination of Engine Brake and Retarder

a combination of engine brake and retarder

One of Scania’s strong suits is the retardation available, the design still uses a combination of engine brake and retarder. This does prove effective, when in cruise control at 100 km/h heading south down the Hume Highway, on a recent road test with a R770 prime mover and fully loaded B-double set, in the constant ascent and descent countryside there are minimal occasions when the service brakes needed to be used. 

The topographical ,mapping in the cruise control system means the truck knows when the up and down grades are coming up and is prepared for them. There is a tendency to bring in the retardation, first engine brake and then retarder, as the truck overruns the set speed. There is enough there to hold the B-double back on all of the downgrades and keep the speed inside the two km/h limit which was set.

a combination of engine brake and retarder

The first service brake application was in the evening heading south out of Sydney, slowing down to park up for the night at the servo in Yass.

The effectiveness and accuracy of the topographical mapping was illustrated on the relatively flat roads passing Euroa. This country is generally flat and there are mild ups and downs as the truck drives along on cruise control. 

As one of the flat sections started to rise the engine was digging in and trying to hold 100, but then, a few hundreds metres before the actual high point, it just took everything off and dropped to 500rpm, and actually allowed the truck to slow. It got down to 94 km/h, just as the truck was going over the peak of the rise and then started gathering momentum, still at 500rpm. It allowed itself to build up pace until it was back at 100km/h. Then it just brought the engine back in and the revs rose back up to 1200. 

a combination of engine brake and retarder

At the start of the rise the engine was at 1200rpm, as it was trying to climb up the slight grade and then coasted slower over the top of the hill, but allowed the slight descent to get its acceleration back up to cruising speed. Even when running at 500rpm you are using some fuel, but you’re using considerably less fuel at idle than at 1200.

The eco-roll tended to be holding on for really long periods on some of these roads. There was a period of several minutes on another section of road, just a slight downhill, going at 100km/h at the top and it just took everything off and it remained like that for quite a while until it hit the bottom at this very slight slope. From the driver’s seat it was not clear which section was downhill and which was flat. But the truck knew.

At the end of the day this is a truck with the most power available and the top torque on the Australian truck market. It does feel like it’s doing it easy, and a lot of the time it is. When it does need to dig in, at the foot of a grade at 60 tonnes for example, it does, and delivers a smooth ride, while only being overtaken by unladen trucks.


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