Latest Scanias brake by wire
Page 14
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by Bryan Jarvis • Scania has developed an electronically controlled "brake-by-wire" system for its latest 4-Series long-haul trucks with disc brakes on both steered and driven axles.
Initially only 400, 460 and 530hp models will have the fully integrated electronic braking (EBS) system, which has been produced jointly with Bosch; the disc brakes are courtesy of Knorr.
Other safety-related developments include a driver's air bag and an optional tensioning device for the built-in seat belt.
Pedal pressure is communicated via the SBV to the EBS control unit. This evaluates pressure signals from each wheel's control unit and load sensing information and electronically relays an appropriate air pressure requirement to the regulating modules and trailer circuit. The air brake circuits are then pressurised and Scania's sliding-caliper ventilated disc brakes are applied at each wheel.
If anything goes wrong with the electronics, the air brakes will automatically revert to C onventional operation.
The rear discs save 30kg, have high thermal efficiency and are less susceptible to fade (see Technology Update, page 36). Pad wear life is about the same as the brake shoe life on a drum brake, says Scania, and rims and tyres run cooler.
Linking the system to the trailer provides maximum braking efficiency with minimal risk of jack-knifing or sliding because of the simultaneous brake actuation on all axle wheels.
EBS is fully compatible with non-ABS trailers but the ultimate aim is match the brake force between unit and trailer. Then, says head of braking development Thomas Persson, both unit and trailer will brake their own weight.
• The EBS system comprises a control module linked to pressure control units on the wheels, ABS
and the trailer control valve. Other connections link the service brake valve (SBV) with its pedal travel sensor, load sensor, wheel speed and brake lining sensor.
Driving impressions To see how a brake-by. wire system performs under normal road conditions CM has driven an RI44 LA4x2NA 530 Topliner with disc brakes on both axles, EBS, Opticruise gearbox and retarder. We contrasted that with a drum-braked 460hp (343kW) R144.
Both units pulled fully laden BPW tri-axled Norfrig reefer trailers but the Topliner's trailer also had disc brakes and was linked into the EBS.
Under normal road conditions we detected no difference in stopping power between the two. The discs gave a harder, less progressive feel at the pedal with slightly more travel but this didn't take much getting used to.
Persson believes that in the interest of safety a combination of disc brakes, EBS and retarder offers an excellent choice for the future. "Scania will definitely be moving to discs in the near future," he says.