The myth of pulse and glide

[WPWoodJr]

Here's an article on the myth of pulse and glide. You may not be getting as great an MPG boost from P&G as you thought.

[justlurkin]

Originally Posted by WPWoodJr

Here's an article on the myth of pulse and glide. You may not be getting as great an MPG boost from P&G as you thought.

The thing with the Prius hybrid system is that if you take your foot completely off the pedal, the hybrid system will induce some regenerative drag to slow the car down-- One can see in the Prius energy display screen regeneration occurs when you take your foot off the gas pedal, and this will limit your glide distance.

So in order to maximize pulse-and-glide in the Prius, you don't actually "glide" with your foot off the gas pedal. You keep a slight pressure on the gas pedal, just enough to prevent the hybrid system from inducing the regenerative drag, so you can coast as far as possible.

This is easily done on the Prius because we have an energy-flow display that tells you if regen is occuring. Not sure if that sort of display is available on your Ford Fusion or if Ford programmed the FFH's hybrid system to induce a similar regen drag. I'd be interested to hear from you how it's implemented in the FFH though!

[a priori]

I've posted a response to Bill on his blog.

It is an interesting exercise to go through the math, but it does a bit of damage to the reality of things.

Until the combination of wind resisitance, tire traction and braking equal or exceed the power of the HSD system to accelerate the, a Pulse and glide will result in more net forward motion than net "stopping effect." What this means is that more energy goes into the acceleration than the glide, so the car willl glide for a longer distance, and it still will end up with greater kinetic energy then at its starting point.

Proof? Cars get better gas mileage than double the FE used during accelration. How else do I explain all of these cars getting such high mileage?

[msirach]

You must be a rookie of Pulse and Glide if you can't realize a true benefit. It is a proven technique.

Originally Posted by WPWoodJr

Here's an article on the myth of pulse and glide. You may not be getting as great an MPG boost from P&G as you thought.

[timberwolf]

I consider this nothing more than an advert by the author for his FFH blog.

[fuzzy1]

The blog author is just performing a simple math exercise based on some assumptions grabbed out of thin air.

He makes no reference to real-world results. The top ranks of the CleanMPG fuel logs are filled by folks who have mastered it.

He also makes no reference to the real-world reasoning behind P&G. To really understand why it can work, one needs to understand an engine BFSC map, which graphs fuel consumption vs. torque and RPM. It is most effective in traditional American pre-hybrids: oversized Otto-cycle (fixed valve timing) engines geared for performance over efficiency, causing normal cruise operation to be very far out of the engine's most efficient operating area. It also helps to use an engine monitor (e.g. ScanGauge), because random guesses about what sort of pulse to use often produce awful results.

Modern hybrids cruise with the engine operating much closer to peak efficiency, so they have less to gain from P&G. I suspect that the best hybrid P&G results are occurring at lower speeds because they are not tuned for their best efficiency at those speeds. Without P&G they still get wonderful results at those low speeds due to the much lower air resistance and their ability to reduce friction by halting the spinning of the ICE.

[Fred_H]

Gigo.

[WPWoodJr]

Originally Posted by a priori

I've posted a response to Bill on his blog.

It is an interesting exercise to go through the math, but it does a bit of damage to the reality of things.

Until the combination of wind resisitance, tire traction and braking equal or exceed the power of the HSD system to accelerate the, a Pulse and glide will result in more net forward motion than net "stopping effect." What this means is that more energy goes into the acceleration than the glide, so the car willl glide for a longer distance, and it still will end up with greater kinetic energy then at its starting point.

Proof? Cars get better gas mileage than double the FE used during accelration. How else do I explain all of these cars getting such high mileage?

You're correct that a good glide will be longer in distance than the pulse, and I wasn't disputing that. I'm also not disputing P&G as a technique.

The interesting thing is the easy misconception that the average MPG during P&G is higher than it really is. To get 60 mpg in my example of a 20 mpg pulse and 100 mpg glide, your glide needs to be 5 times the length of the pulse - I believe that is counter-intuitive to most people.

[WPWoodJr]

Originally Posted by justlurkin

The thing with the Prius hybrid system is that if you take your foot completely off the pedal, the hybrid system will induce some regenerative drag to slow the car down-- One can see in the Prius energy display screen regeneration occurs when you take your foot off the gas pedal, and this will limit your glide distance.

So in order to maximize pulse-and-glide in the Prius, you don't actually "glide" with your foot off the gas pedal. You keep a slight pressure on the gas pedal, just enough to prevent the hybrid system from inducing the regenerative drag, so you can coast as far as possible.

This is easily done on the Prius because we have an energy-flow display that tells you if regen is occuring. Not sure if that sort of display is available on your Ford Fusion or if Ford programmed the FFH's hybrid system to induce a similar regen drag. I'd be interested to hear from you how it's implemented in the FFH though!

In the FFH, there are three types of regen - regen from braking, regen from the ICE when it is providing more power than the car needs, and regen from taking your foot off the pedal. Regen from braking is displayed on the battery SOC display on the dash as 3 arrows in a circle; regen from the ICE or lifting your foot from the pedal is displayed as an upwards-pointing arrow. If the FFH has nav there is also a large power-flow diagram similar to the Prius but it is harder to read - no color-coding and the arrows that indicate power flow direction are small and hard to see while driving; so I don't use this much.

On the FFH its hard to keep the balance between regen and acceleration during a glide. Its much easier to put it in neutral for the glide, but then you lose all regen capability so I don't use neutral often. I find where I drive that I usually either need to slow down, so I let it regen, or I need to keep the glide going longer, so I apply a little EV power.

[ksstathead]

... and that's why P&G is primarily a low-speed technique, avoiding the worst of the wind resistance. It also helps to have LRR tires, tires at higher pressure, perfect alignment, etc.