The world is quickly moving towards more hybrid and electric vehicles, which reduce toxic emissions. This trend is leading to an overall improvement in the quality of the air we breathe, especially in congested inner city locations. During this evolution, bus and coach manufacturers can get ahead by taking advantage of the latest electro-hydraulic steering systems to reduce the size of their internal combustion engine (ICE).
Replacing hydraulic variable displacement pumps with more efficient electrically-driven systems allows ICE downsizing and emission reductions to begin.
A brief history of power steering systems
The first power steering systems for buses and coaches were designed with a variable displacement hydraulic pump, which was driven by a belt connected to the ICE. Originally, the required size of the ICE was dependent upon the amount of power needed to propel the bus or coach as well as the additional auxiliary power needed for hydraulic and pneumatic functions. As these gave way to the power take-off (PTO) system—and then the electric generator powered by the ICE—steering systems slowly began to become more efficient and engines could get smaller.
The electro-hydraulic steering pump
The most recent iteration of power steering systems is an electric generator driven by the ICE with an electro-hydraulic pump for the steering function. A new range of permanent magnet AC (PMAC) motors dedicated to mobile applications are currently the most efficient available on the market, and this efficiency level combined a smaller motor size allows it to be installed at the front of the bus, improving system efficiency further by shortening hydraulic connections from pump to steering box.
These systems will continue to improve as time goes by. Designing a more ergonomic system to provide the hydraulic power for steering is one direction for future development by OEMs. The introduction of electro-hydraulic pumps is a first step in the vehicle hybridization process that will one day lead to complete electrification for transport systems in large cities.
By understanding that each vehicle electrification application has its own unique requirements, we can support your vehicle development by delivering high performance solutions in electro-hydrostatic systems, electric and hybrid drivetrain systems and auxiliary vehicle systems.
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Article contributed by Bruno Jouffrey, market development manager - mobile, Electromechanical and Drives Division Europe, Parker Hannifin Corporation.