Article,Features,Hypermiling

Pulse and Glide

17 Jul , 2016  

– Tony Schaefer

In this post, I will attempt to provide a simplistic overview of a hypermiling technique known as “Pulse and Glide” (P&G). Before we get started, you need to know that the application and technique for P&G is variable based on many factors such as the car, terrain, traffic, current speed limit, etc. For all those reasons, this will be an overview and not overly detailed. My concern is that if I provided any real details: 1) you would try to apply the details where they don’t fit, and 2) someone will argue the minutia of the details.

How Do You Pulse and Glide?

Many times, I compare hypermiling to riding a bicycle. This works because almost everyone knows how to ride a bike, which makes it a universal reference. Also, you most likely remember how tired you can become if you do not ride efficiently. Though neither you nor your car will get tired, you have to focus on the amount of effort being exerted; the goal is to travel farther with less effort.

The Pulse. Just like riding a bike, the intent of the pulse is to get up to speed. When accelerating from a dead stop, use a brisk acceleration: accelerate quickly but not stomp on the gas. Once you have reached a speed that is, perhaps, a little faster than the speed limit or average traffic speed, let up on the accelerator.

The Glide. Think about riding that bike. Once you have reached a decent speed, it requires only a minimal amount of effort to maintain it. In fact, depending on the situation, you might be able to coast for a long distance before needing to pedal again. In exactly the same way, the point of the glide is to “stop pedaling”.

The first and second generation Prius were exceptionally good at gliding because they had a “dead band”. This dead band is a spot in which there would be no power coming from the engine or batteries to drive the wheels and also no regeneration from the wheels to the batteries. A practiced driver could work the accelerator into that dead band and let the car roll.

Unfortunately, this type of “free wheeling” is nearly impossible in almost all modern hybrids. And so it is with modern hybrids that the glide is an attempt to reduce the energy flow to a point as low as possible.

Pulse Again. As you can imagine, after coasting for a while, you will start to slow down. Once you’ve slowed to a speed you are no longer comfortable with, pulse again. Unlike the dead-stop pulse, this time you want to use just enough acceleration to get back up to speed. Just like riding that bike, it’s not a sprint back up to speed but rather just enough.

And then you glide again. Then pulse, then glide, repeat.

Why Does it Work?

The concept is simple: the entire intent of P&G is to glide more than you pulse. The following image provides a sort-of representation starting from a dead stop, accelerating up slightly above the desired speed, gliding, pulsing, and then gliding again. As you can imagine, the farther you can glide the better. The black line in the following image might represent the average traffic flow, the speed limit, or simply the speed you want to average. Your situations will vary.

Pulse and Glide Image

It works because gliding is essentially free. It’s the pulsing that costs you. Therefore, rather than paying to constantly maintain a steady speed, you allow your speed to vary. The trick comes in making sure the pulsing uses less effort than would otherwise be used maintaining a steady speed.

Situational Considerations

  • As with all hypermiling techniques, obey all posted traffic signs and do not impede the flow of traffic for your selfish desires.
  • If you have rolling hills, that is awesome. Pulse up the hill and glide down the other side. They key is being able to gauge the most efficient time to transition from pulse to glide and vice versa.
  • One hypermiler told the funny story of being pulled over because the policemen observed he was “incapable of maintaining a steady speed” and assumed he was drunk. I didn’t say it was funny for him. He said that once he explained what he was doing, the policemen didn’t bother writing a ticket.
  • If you see a stoplight up ahead, consider modifying your pulse and glide timings to either glide into the stop or pulse a little faster to ensure catching the green light.

 

 

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