How ‘intelligent’ the steering system for the electric vehicles should be?
In conventional gasoline and diesel vehicles, we find that the steering system is a Rack & Pinion type steering system. If not hydraulic, it is a manual Rack & Pinion steering system. In case of a manual Rack & Pinion steering system the steering torque will be higher if the front axle weight (FAW) of the vehicle is high. To reduce the steering torque the alternative available is a Column type electric power steering (note: in case a hydraulic type Rack & Pinion steering system is fitted in the car then its steering column will be a manual one; not electric type).
When a conventional vehicle is fitted with a hydraulic type Rack & Pinion steering system then power is required to run the reservoir (containing hydraulic oil) and the hydraulic pump connected to it. This is done through the pulley system connected to the crank shaft gear. Now higher the vehicle load then higher the steering torque thus higher the power to run the system is required.
Running an electric power steering system in an electric vehicle?
Consider an electric vehicle to be run with an electric power steering. The power source here will be a rechargeable battery system. A rechargeable battery system can only be recharged with a regeneration system or utilising braking energy. Other than this there is no source to supply power to run the electric power steering system. The question arises, how we will be able to run the steering system in case of complete battery discharge? Or in case of the electric fault?
The “Intelligent” system?
In hybrid cars the electric motor takes over from the gasoline motor as the vehicle speed drops. It switches back as the speed increases. To summarise, at lower speeds the electric motor runs the car and at higher speed the gasoline motor kicks in. At higher speeds, the generator charges the battery pack. So, in case of hybrids there is an alternate source available which is assisting the vehicle electric system. But in case of pure electric vehicle, what are the alternatives available? Note that as we keep on adding the alternatives, it increases the vehicle weight. The power to weight ratio should be an area of focus. More wight means more power is consumed.
What are the solutions?
Through controlling the driving torque of the two in-wheel traction motors, a proper power steering assist torque can be generated, which can be used to make hydraulic pump or direct power steering motor completely unnecessary and the power steering system can be designed with more compactness, and operated with high efficiency and less maintenance requirement.
Some more points for consideration:
- An APU (Auxiliary Power unit) other than the battery pack, which kicks in when the main battery system exhausts completely.
- The braking system connected to alternators which charges the battery pack, during deceleration.
- A solar panel on the roof, which works as a back up.
- Separate motors on both front wheels to run the steering system in conjunction, as explained above.