Features,Hypermiling

Braking

5 Mar , 2016  

– Tony Schaefer

From time to time, someone will ask, “what is the best way to brake?” This is a really good question because there are actually different ways to brake. Just to be clear, occasionally someone will do something very stupid in their car that will create a situation in which you must ignore everything you are about to read. In no way should you value hypermiling over your safety, the safety of your occupants, or the integrity of your vehicle. Everything you are going to read in this post refers to non-emergency situations.

I’m going to start off with an explanation of how Prius regenerative braking works. Why? Because I drive a Prius and that’s what I’m most familiar with. Also because it’s very likely regenerative braking in other cars works very similarly.

The Prius has three different types of braking that I am going to call “Passive Regen”, “ Active Regen”, and “Physical Braking”. Just to be clear, those who are more technical could easily break the whole thing down into mechanical terms but that’s not the approach I’m going to take. If you’re looking for the details, there are plenty of complicated explanations elsewhere. Complicated things scare and confuse me.

Passive Regenerative Braking

Let’s say you are driving along and let up on your accelerator. The Prius will use the spinning of the wheels to physically turn the electric motor. When you physically turn an electric motor, it generates electricity. This is the principle on which wind turbines work. But in a car, the momentum of rolling is transferred into effort required to turn the electric motor resulting in deceleration. So when you are letting the car slow down on its own, you are generating electricity that is captured in the battery.

Active Regenerative Braking

Let’s say you are approaching a red light. You need to press on the brake pedal. If you press lightly on the brake, the Prius will apply electrical resistance to the electric motor. This electrical resistance accomplishes two goals: it creates added resistance that will slow the spinning of the wheels and it generates more electricity than passive regen.

Physical Braking

At speeds below 7 MPH, the Prius skips the whole regen thing and goes straight to applying the brake pads to the rotors. Additionally, if you are traveling at any speed above 7 MPH and stomp the brake pedal, the Prius assumes it’s an emergency and goes straight to pads-on-rotors. My assumption is that any vehicle with regenerative braking would do the same thing.

Now that you understand the three primary types of braking, it should come as no surprise that the worst type of braking is the physical braking. This is because there is no electrical regeneration captured. In fact, the worst possible braking technique would be to wait until the last second and stomp on the brakes. Not only does this pretty much ignore regenerative braking entirely, it puts a lot of trust into the braking system. Granted, it’s the 21st century and the brakes in advanced-tech vehicles should never fail. But why test that theory?

The best method for braking is a long slow active regenerative braking. If you see a red light in front of you, apply a little pressure to your brake pedal. The regenerative system will kick in and you will capture a decent amount of energy. If the light is really far away, then coast for a bit, picking up some passive regen and then apply the brakes for active regen.

Here’s the problem: most other drivers don’t drive hybrids, don’t worry about regenerative braking, and don’t care one iota that you do. They actually prefer to race towards the red light until the last second and slam on their brakes. This is why when you start braking long before the red light they are going to either become very frustrated behind you or they are going to zip around and get in front of you. No one said hypermiling is a feel-good endeavor. This is extremely frustrating but if you are truly interested in posting crazy-ass hypermiling numbers, you must learn to accept it and get over it.

So that’s it. Worst way to brake is to slam on the brakes and ignore any attempt to recapture energy. Best method is long slow active regenerative braking. But you must always be aware of the drivers around you and how your actions might affect them. I said it before and I meant it: if it reaches a point in which you annoy people for your hypermiling gains, then you’ve already lost. Never annoy other drivers.

In the interest of full disclosure, I must mention that the best method for braking is to not brake at all. In my article, Try to Avoid Braking Altogether, I discuss ways to go easy on the brake pedal.

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