- Servotwin® steering system supports implementation of assistance functions
- New rear-axle steering system is considerably more efficient
Efficiency and driver assistance are aspects that are currently attracting a great deal of interest in the commercial vehicle sector. Bosch is applying its extensive steering systems expertise in the passenger car segment to commercial vehicles. These innovations enhance safety and convenience in buses and significantly reduce fuel consumption and CO2 emissions. The Servotwin is the world’s first integrated electro-hydraulic steering system for production vehicles in the heavy commercial segment. This steering system with superimposed torque offers a great many benefits in buses too. The basic version provides speed-sensitive steering assistance and an active return to the straight-ahead position. The new-generation Servotwin additionally supports the implementation of driver assistance functions, which enhance safety and convenience in commercial vehicles. The Servotwin constitutes the core component in such assistance technologies.
Electronic assistance in buses
The lane keeping function prevents the vehicle from inadvertently wandering out of the lane by means of either corrective steering intervention or a warning signal. But that is not all: there is also an assistance function that eases the driver’s workload in traffic jams and stop-and-go traffic. In this case, the system maintains a set distance to the traffic ahead. The driver monitors the system and can override it, taking control at any time. Crosswinds pose a serious risk to heavy commercial vehicles due to their large surface area. To counteract the adverse effects of such suddenly occurring winds, a dedicated assistance function offsets the wind forces. In such situations, the steering system’s control unit determines the steering correction needed and applies it via the electric motor. In addition to these benefits, the Servotwin steering system also has a positive effect on the commercial vehicle’s efficiency. Depending on the driving cycle, Servotwin achieves a fuel saving of around 0.6 l/100 km compared with a conventional steering system.
Smart rear-axle steering system
The rear axle steering system (eRAS) has been completely redesigned and is now electronically controlled and electrically driven. As a result, the new eRAS features a power-on-demand function, so energy is only required when the steering is actually being used. The electric motor drives a pump that generates hydraulic pressure via an operating cylinder that is transferred to the rear axle. This on-demand provisioning of the steering power allows fuel savings of around 0.6 l/100 km to be achieved. The eRAS requires neither a mechanical nor hydraulic connection between the front and rear axle. This makes the system equally suited to volume-production integration and retrofitting. All the important geometric parameters, such as wheelbase and steering angle, are individually programmed in the steering control unit. Particularly buses with a large wheelbase benefit from smart rear-axle steering. Firstly, it reduces the bus’s turning circle – an advantage that especially becomes apparent in urban environments. Secondly, the eRAS increases vehicle stability and driving safety at higher speeds, for instance, during lane changing. Both Bosch systems enhance safety and convenience while at the same time considerably reducing the fuel consumption of commercial vehicles.