Electric Vehicle – The Art of Hypermiling
In the previous post on hypermiling the concept was desribed mostly from the technical aspect of an electric vehicle or a hybrid vehicle. In this post the focus will shift to the practical side of things: how to drive and behave to go hypermiling in your vehicle.
In short, the art of hypermiling is about how to drive in order to get the most range from a full charge or tank. It describes how to drive with the highest energy efficiency and conserve energy when possible.
There are a few areas to focus on when hypermiling. The first is acceleration and deceleration. The second is speed and a third is air resitance.
The Battery: what does acceleration and speed do?
As mentioned in my other post, inside a battery, the chemical process of storing a charge or discharging, is always with a loss. This effect is best noticed as the temperature of a battery increases at high loads over a long period of time. This is often described as the internal resistance of a battery.
A battery model, the internal resistance (Ri) results in the (heat) losses associated with (dis)charging.
In the simple battery model shown above, the power the vehicle consumes is drawn from the right hand side. The storage of the charge is shown on the left and the internal resistance is indicated with Ri.
A small brush up on physics/electronics first. When large powers are drawn, large currents go through the (closed) circuit. In that case, the resistance creates a bigger (heat) loss in the battery. This process also works in the opposite direction, when the battery is charged again. For the mathematical background of this matter I’m working on creating a Prezi to clarify things more. As an alternative, contact me through Linked In, Facebook or Twitter and I can send you some information.
What this concept implies in reality, is that drawing large powers comes at a higher loss. If you focus on hypermiling, drawing smaller amounts of power is a key priority. The amount of power you draw is affected by two driving factors: acceleration and speed. If you floor the pedal and drive at maximum speed you draw huge amounts of power, facing larger heat losses and reducing your range. The most efficient drive would then be at the lowest possible power drain. In other words: a rather dull ride. The key is to find the balance between getting somewhere in a timely manner and not accelerating too much or speeding too fast.
Which is more efficient, the tortois, or the hare?
Charging the Battery
The power story also holds for regenerative braking. When you brake, you can recoup energy through the regenerative braking. If you brake hard, you generate more power, but also have higher losses. Also if you brake really hard, often the mechanical brakes kick in which result in even higher losses of this recouped energy. The best approach here is to preferably let the vehicle roll to a stop and decelerate on the electric motor mostly. This ensures the lowest possible power flow that is recouped and has the smallest losses.
The air resistance of your car is ideally very low; which means the air is not acting as a force on your car. Things that can help you improve (lower) your air resistance is for example having your windows closed. This ensures that air will move more gently around the vehicle and not create unwanted drag. Another example is driving in the slipstream of another vehicle, a technique that is also seen by professional racers. First and foremost: This is not a technique I recommend, it can be rather dangerous to do this, so do this at your own risk! The idea is to drive behind another vehicle (large trucks are ideal because of their large area) and not catch the airflow directly onto your car. It becomes obvious that driving closely behind a big truck almost takes away any clear view of the road ahead; if the truck stops suddenly you are in big trouble!
Airflow around a vehicle. Driving right behind it (in the slipstream) reduces your own resistance (but is not recommended!)
To sum things up, it is best to drive somewhere in between a tortoise and a hare; not too fast so you can get more miles, not to slow so you actually get where you want in time. Low powers are more efficient for the battery to handle and yield a higher range in the end. Let your car roll out to a stop to maximize the energy you can recoup from braking. Also keep the windows closed to improve the air resistance, but do not drive in a slipstream at high speeds behind some other vehicle.
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