A reader responded to my last post on mileage: “Personally, I like to accelerate briskly up to speed and then let up on the juice just enough to kick the engine off (the "pulse and glide" technique). This technique works for full-hybrid cars like the Prius that can run on electricity alone, but may not apply to other hybrids that require the engine to run when the wheels are turning.�
Toyota uses an ingenious geared, power split device to input power from the gas and electric engine into the CVT (continuously variable transmission). It's durable, has no slipping parts, like a Positraction Clutch Pack on a 57 Chevy, and should last the life of the car.
The computer either sends a signal to power the electric motor and/or the gas engine, or both. There can also be a split of power where gas and electric each provide a percentage of power. The computer also controls the transmission to provide the best gear ratio to power the car as efficiently as possible or less efficiently if you have your foot on the floor telling the computer that you want to merge on to I-83 north bound from Market Street.
Here is a site with some great pictures and description of the Toyota power split device.
http://www.cleangreencar.co.nz/page/prius-technical-info
The nature of this ability to “choose� the power inputted into the power split device in the Prius is what drives the “pulse and glide� technique. It’s unfortunate that things like people and other cars get in the way. I would imagine this technique might get you in trouble if adhered to obsessively on I-83 during rush hour.
Honda uses a system with an electric motor sandwiched next to the flywheel. The brushless electric motor always spins at the same rate as the gas engine. The computer controls the amount of power boost to the electric motor and allows power to increase from the gas engine. The combined power feeds a CVT.
Honda's design allows the use of a CVT as well as a manual transmission, which Honda has dropped in the redesigned 2006 Civic this year in favor of a drive in electric mode only. Honda heavily surveyed me after I bought the car in Dec 2004. The word "e-drive" kept popping up in questions. It appears that the American public thinks that it’s cooler to start in electric mode than to have a manual transmission option. I have always liked manual transmissions.
In both systems, a small engine with high gear ratios is boosted by an electric motor. Since a driver-operated clutch is based on transmitting torque by varying engine speed and slippage, you can see how a power split device, two inputs of power controlled by a computer and a drive by wire accelerator pedal, would be a nightmare to design and possibly operate with a manual transmission.
Maybe someone with a 2006 Civic Hybrid can tell us if they can “pulse and glide� to high mileage heaven?
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I would imagine this technique might get you in trouble if adhered to obsessively on I-83 during rush hour.
--It's been my experience that this technique only works well when it's not noticeable. If I'm frequently speeding up and slowing down, then it's not really saving me any fuel and it's probably annoying other drivers. To me, "pulse and glide" means applying a brief pulse of power using the engine to get up to cruising speed, and then gliding with the electric motor to maintain that speed. It doesn't take much horsepower to pull the car on relatively flat terrain or downhill. It's actually a fun game to see how long I can flow with traffic without having to engage the engine.
--By the way, thanks for the informative post!
Who would ever think an automatic transmission would be so much fun to drive! You have inspired a new post in the making.
I would like to know if you can use the pulse and glide in regular cars also and if it works to save gas?
Hello Helen, thanks for stopping by...
The heart of the pulse and glide success is that the Prius regenerates electricity on the glide and the pulse uses the gasoline engine at its maximum efficiency and then doesn’t use it. The technique is based on the technology in the Prius.
However, in the same way people get to know their Prius, you can get to know your own vehicle and benefit. Mileage on any car will increase by driving it gently. Acceleration burns up the most fuel. Many cars reduce fuel flow when decelerating.
This is one of the reasons diesels are so efficient, because they change the fuel mixture based on driving condition. At idle, a diesel may be running at 150:1 fuel to air mixture. Gasoline engines tend to keep the same air to fuel mixture around 15:1 and the volume of the mixture is proportional to engine speed.
At really high speeds it starts to take huge amounts of energy to keep your car in motion as air drag and friction take its toll.
Easy acceleration, keeping the speed limit and driving with anticipation to reduce rapid stop and go can improve mileage in any car.