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Journal of Automobile Engineering .
Ian James Spark1, Andrew Percy2
- Federation University Australia, Churchill, Victoria, Australia.
- Federation University Australia, Churchill, Victoria, Australia. Email:[email protected]
Abstract
This paper presents the results of calculations of the wheel angles and the drive wheel speeds to ensure that the steering effect of the wheel angles and the steering effect of the speeds of the drive wheels are identical. These calculations are general insofar as the centre of curvature of the path of the centre of the vehicle can lie anywhere in the ‘horizontal’ plane, including within the plan view of the vehicle. These minimal turning circles at times require large wheel angles and large differences in the drive wheel speeds. When the driver selects a centre of curvature inside the rectangle defined by the wheelbase and the track, problems arise owing to the multiple solutions of the arctan function. This problem is solved so that flipping of the wheels through 180° is avoided. Similar problems can arise in the calculation of the correct wheel speed because of the ambiguity of the square root function, which has both positive and negative roots. This problem is also solved. Alternative driver interfaces are described in detail. Vehicles with cooperative redundant multiple steering systems promise safety benefits relative to vehicles with a single non-redundant steering system and environmental benefits relative to vehicles with conflicting redundant multiple steering systems. The safety benefits result from increased traction, stability and manoeuvrability (especially on hills). The environmental benefits include reduced ground damage, tyre wear and fuel wastage on turning. These vehicles would be used to best advantage as extreme off-road vehicles. The general case of vehicles described is capable of both pure rotation and pure translation in any direction, and all motion in between. This maximized manoeuvrability also makes the system ideal for vehicles operating in confined spaces, such as forklift trucks.
Significance statement
The authors have conceived and modelled two new wheeled vehicle types based on the principle of cooperative redundancy between two or more steering systems (CRMSS). US and Australian patents have been granted.
Traditional systems use either a single non redundant steering system (e.g. traditional tractors) or conflicting redundant steering systems (e.g. skid steer vehicles). The former have the environmental advantages of minimal ground damage, tyre wear and fuel consumption. The latter have the safety advantages of maximum manoeuvrability, traction and stability. It is not generally recognised that the advantages of both systems can be combined (or exceeded) with a (CRMSS).
In the extreme off road application of CRMSS, an on-board computer is used to ensure that the steering effect of wheel angles is identical to the steering effect of positively driving the left and right wheels at appropriate speeds.
CRMSS can be used to best advantage in vehicles operating at the limit of traction. It could be used to replace the following traditional vehicle types:
- Industrial mowers
- Skid steer loaders
- Articulated Loaders
- All terrain fork lift trucks
- Rigid and articulated(mining) dump trucks
- Agricultural vehicles
- Forestry vehicles
- Military vehicles
- Recreation vehicles and all terrain wheel chairs
Although the new vehicles should out- perform existing vehicles, they need to be designed from the ground up so that their appearance may not resemble that of vehicles they are replacing. However most can be built by installing off the shelf components in a purpose built chassis. CRMSS vehicles would enable their manufacturer to leap frog ahead of traditional manufactures (which are dominated by US, Japanese and Korean-based multi-national companies).
A more recent application of the principle of cooperative redundancy is to improve the performance of B-double semi trailers and road trains in general. CRMSS can be used to make the trailers run on virtual rails (thus eliminating corner cutting) while eliminating scuffing.
The safety advantages are reduced off-tracking, increased manoeuvrability, easy (un-skilled) reversing and high resistance to jack knifing. The environmental advantages are reduced road damage, tyre wear and fuel consumption. Although this on road market for CRMSS is much smaller than the extreme off road market, it has the advantage that it is not dominated by large multi-national companies.
