As the trend for passenger cars and light commercial vehicles is toward electric power assisted steering (EPAS) and ever heavier vehicles are converting to EPAS such as the Ford F150 Pick up truck, how much longer will it be before Heavy Commercial Vehicles get EPAS?
EPAS was always discounted for heavier vehicles due to the electrical current requirement to assist the steering effort for vehicles with such a front axle weight, even though they are all 24v as opposed to 12v for passenger cars and Light Commercial vehicles. The Ford F150 above and the next generation of Range Rover are already finding 12v sufficient; the advances in motor technology are already making it possible to put EPAS on heavy 12v vehicles. For some time there has been talk that trucks will need to go to 48v due to the ever increasing load on the battery with all of the electrical systems, and recent articles in the commercial vehicle press suggest that 48v is only “just around the corner” (interesting steering connection) due to ever increasing number of electrical systems requiring heavier current draw. Add to that the increasing number of Hybrid vehicles, especially in the light of Government initiatives in the bus market, with the Green Bus Fund in the UK being mirrored in other EU countries to meet governmental commitments to the Kyoto agreement, more current will become available to enable EPAS on heavy vehicles.
However, EHPAS (Electric/Hydraulic Power Assisted Steering) is a halfway house, where an electric motor is driving the hydraulic pump, but all the rest of the system remains the same. Some small fuel savings are possible as the pump only draws current when there is a steering demand.
However I believe that the cost of development for EPAS for such vehicles and the number of production vehicles that can carry the development cost will delay its introduction until there is another driver.
One of the drivers for the passenger car industry to take up EPAS has been fuel efficiency and emissions. In passenger cars, significant fuel savings can be realised due to the power for the assistance only being required when the steering wheel is actually moved, and the amount of power required is directly proportional to the effort, whereas traditional hydraulic power assist requires an engine driven pump to be pushing fluid around the system even when the vehicle is stationary. This fuel saving of course immediately translates to reductions in emissions.
The savings that could be achieved in heavy commercial vehicles is similar, but as a percentage of the current fuel consumption of such vehicles is small beans. A further driver however could be the introduction of steer by wire (SBW). The latest revision of ECE R79, the European regulation of steering in motor vehicles, makes provision for steering systems that have no mechanical connection between the steering wheel and the road wheel. New electronic architecture is required to provide for sufficient redundancy in the event of failure, but agricultural equipment has been using auto steer on tractors and harvesting machinery for about the last 10 years, and a report by the Steer By Wire working group www.ttagroup.org suggests that steer by wire will have reached 25% of the agricultural vehicles by 2015 and 100% by 2018. Currently the off highway market has more drivers for SBW as it is easier to integrate auto steer, but that would become even easier with EPAS.
I believe that the heavy commercial vehicle industry will not go to EPAS until such time as SBW is proven in off highway vehicles, 48v becomes necessary and the increase in hybrid vehicles and the development of them reaches a level that makes good economic sense. Increases in fuel prices and the drive for more efficient vehicles will speed up the process, but I remember 15 years ago when everyone was talking about electric steering being the future. It has taken this long for the car industry to build confidence in electric steering, and the drivers for it to become financially viable to change, so therefore, although I would expect to see both steer by wire and EPAS to become reality, I would not expect to see it prevalent before 2020. What are your thoughts?
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