VOLVO VDS STEERING PAVES WAY FOR AUTONOMOUS BUSES
Following the 2013 launch of Volvo’s Dynamic Steering system on trucks, it has now been developed and launched for bus and coach applications with both rigid and independent front suspension. It is immediately available for all Volvo chassis and complete coach applications, though not yet on the line vehicles – it will be offered on the 7900, 8700 and 8900 city and intercity vehicles later this year. This includes the 7900H Hybrid.
An exception is the double-decker, It is not yet being offered for applications like the B5TL for reasons linked to the lack of space to mount the electric VDS motor within the front overhang. But it is already available on the 9800 coach for Mexico, which is a Euro 5 product.
The aim of introducing systems like Volvo Dynamic Steering is reaching zero traffic accidents, something that may be achievable in the future with autonomous vehicles, and Volvo is working toward that aim by focussing how to avoid accidents in the first place and developing vehicles with superior handling properties and advanced safety systems, supporting the driver to operate the bus in the safest way possible.
Volvo Dynamic Safety (VDS) offers a safer and more comfortable ride by detecting irregularities and calculating the necessary compensation in order to give a desired, pre-determined steering ‘feel’ independent of load and tyres. At low speeds, an electric motor amplified the force to provide most of the power required for steering, thereby reducing the toll on the driver’s arms, back and shoulders. At higher speeds the increased directional stability creates a more relaxed driving experience.
Volvo has added an electrically operated motor to the steering system, attached to the steering shaft which works in tandem with the hydraulic power steering.
This motor receives signals from the electronic control unit 2,000 times a second informing it of the vehicle speed, steering angle and the torque applied by the driver. From these signals, the software in it calculates the optimal level of input to deliver to assist the driver. At low speeds, and particularly during manoeuvres such as parking or reversing, the electric motor generates additional power, while at high speeds the steering is automatically regulated, compensating for irregularities which pass up to the steering wheel, from deformations in the road surface. Volvo claim that when driving at low speeds, steering wheel inertia is reduced by around 75%.
The primary advantage is to the driver in reduced fatigue, as well as in the improved ride on rough surfaces.
The electrical motor is supplied by CPAC, a part of Volvo that also makes drive components for Volvo Penta. It is a 23Nm unit which, as the torque needed to change lanes is around 4-5Nm, should be working well within its range. The motor senses the torque from the front wheels via the torsion bar and instantly reacts.