Smart Scanias' exhaust braking

DEVELOPMENTS: Scania has a retarder that is powerful enough to restrain a B-triple on a Mt Ousley-like descent without the service brakes.
DEVELOPMENTS: Scania has a retarder that is powerful enough to restrain a B-triple on a Mt Ousley-like descent without the service brakes.

THE thudding exhaust brake has long been the bane of residents along side main streets of small country communities.

Particularly when there's a long hill descent into town where the speed limit comes down from the open road 100kmh.

It used to be on or off, with plenty of leaky manifolds from the pressure built up over a several kilometre descent. If you've heard the classic crazy call between a Melbourne radio announcer impersonating a transport inspector, and 'Wayne', a truckie who took exception to be told he was using his exhaust brake too much, you'd know that the signs asking truckies to avoid engine braking are not very popular.

But the evolution and development of exhaust brakes, tied to the more powerful hydraulic retarders has brought engine, gearbox and brakes much closer in integrated operation.

A key mover in this technology area was Clessie Cummins, the man who founded Cummins Engine Company with a business partner in 1919. Clessie was a bright spark firing in damp wood until Bill Irwin got him organised. What isn't often recognised is that one of Clessie's greatest innovations, and certainly the most profitable for him was the Jake Brake, a device that his old engine company passed up. Various systems are championed by manufacturers, all the way from weak and ineffective exhaust brakes on some of the Asian trucks, to powerful retarders that are engineered as a component of some European gearboxes.

As is the case with a number of the Europeans, Scania's current models use advanced computing to bring driveline components into harmony to assist with efficient and smooth braking, gear-changing, torque maintenance and even warm-up of the engine and retarder.

In particular, the Opticruise AMT enlists the help of the exhaust brake during gear-changes under load and steep inclines. Basically, by selecting power mode on the transmission selector switch, the Swedish gnomes lurking under the floor slow the engine between gear-changes to help Opticruise keep torque flowing to the road with as few interruptions as possible. So the exhaust brake and retarder become essential components in effectively going up steep hills under load.

But there's more! Many of the Scania markets drive during colder weather and frequent snow and ice, like Tasmania recently (-4 in Launceston!). In these areas sub-zero temperatures quickly seep through cabs, engine covers and engine blocks, as well as transmission components.

A truck left overnight in these areas quickly becomes vulnerable to cold start wear and tear, with oil that is thicker and tolerances tighter.

Taking off in your new Scania for example, as you're accelerating the engine computer engages the exhaust brake and retarder and immediately sparks a competition between power and braking inside the engine block. It's a rapid warm-up program that is disengaged by a dab on the service brakes.

This tells the system that you're ready for normal driving and the auxiliary brake system goes back to working when you're off-throttle only. Scania's Ian Butler told us of an additional trick that the electronics have up their sleeves. After a longish period of cruising, the oil in the retarder has subsided.

When you go off-throttle, the system reads the oil level and applies the service brakes at the same rate that the retarder would generate normally. Once the oil pressure is at operational level - that's within a second - the system seamlessly lets go the service brakes as the retarder takes effect.

You can pick it if you listen carefully, but you really can't feel a thing through the seat or the wheel.

Triple braking systems make today's heavy-duty trucks potentially the safest vehicles on the road.

Unfortunately, most factory gurus know that few drivers use all the features they have at their fingertips.

Until they understand the technologies and use them, operators will see more dollars slipping through their fingers on fuel, tyres, brakes, clutches and accident damage.

Topics:  scania



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