Hi,

I've just purchased a new Civic Hybrid in Magnetic Pearl with Navi, and I've been catching up on some reading here at Greenhybrid.com. I've managed to get the pulse and glide to work, but I can't understand why this would save me gas. Let me explain...

When performing pulse and glide, you are pingponging energy between the battery and ICE. During the "pulse" phase, you are accelerating to speed and charging the battery. During the "glide" phase, you are decelerating slowly and discharging the battery. In this scenerio, a certain amount of energy is circulating from the ICE to the battery during the pulse, then back to the drive train during the glide. In a perfectly efficient system, this should be a wash. Just as much energy is stored into the battery by the ICE, that is later used for powering the car. However, all systems are ineffiecient. Let's say that you lose 10% of your energy when charging the battery, then another 10% when running the electric motor. That's a pretty efficient system, but you still lose 19% power when routing power through the battery vs. routing the power straight to the drive train. Doesn't it make more sense to simply run the drive train with the ICE in the first place? Every time you use the ICE to charge the battery, you are losing some power that the ICE has produced. So the pulse and glide should be the least efficient way to drive, not the most efficient. The most efficient way to drive is to leave a constant load on the ICE. This is the case when cruise control is engaged.

The advantage of a hybrid is not the fact that it has an electric motor. Every time you use the electric motor, you are losing energy. If this was not the case, then hybrids would work the way an diesel-electric engine works--the ICE charges a battery which runs the engine. The real advantage of a hybrid is that it is able to recover energy that would otherwise be lost from the system. Energy such as deceleration (braking). The most efficient hybrid configuration would actually never use the battery at all during an initial acceleration period and cruise. It would recover energy during deceleration, which could then be doled out during other acceleration periods. Creating false accelerations and decelerations via pulse and glide activates the electric system more often at the expense of effienciency.

The one time when pulse and glide seems to make sense is if you have an overabundance of recovered energy. In that case, you would want to use the potential energy of the battery to assist in normal driving as much as possible, if only to prevent the battery from "overflowing" and losing energy. In other words, you don't want to charge a full battery when decelerating. If this is happening, then pulse and glide may be a way to transfer more energy from the battery to the drive train. But it seems a better solution is just to tweak the car computer to more aggressively assist when the battery is nearly full. I suspect Honda has already done this.

So, does pulse and glide really work? I'd like to see some controlled experiments to be sure, but I suspect that it actually defeats FE in many cases. Simply driving conservatively at a constant speed will yield better results. If you are driving in a fashion that generates an overabundance of regen energy, then pulse and glide *might* allow more of that energy to be realized. But it seems there are better ways to do this.

I suspect that running on the electric motor only is mostly a psychological boost to performance. Every watt of energy in your car is produced by the ICE. If you are running off the electric engine, you are actually running less effiently than the ICE. The advantage of the electric engine is that there is a way to recover and store energy, whereas there is no way to un-combust gas.

Let me know what you think. This is all theoretical, but I'd like to know why pulse and glide works or doesn't.

--Brad