Energy Use

<div class='quotetop'>QUOTE(niepo @ Jun 10 2006, 10:30 PM) [snapback]269346[/snapback]</div>

THS II has "advanced energy management" for the entire vehicle and has achieved improved fuel efficiency. Excerpt:
[attachmentid=3762]

 

Some day we might have plug-in hybrids, but right now you're correct that all the energy that the car has is the fuel in the gas tank. The difference with the Prius is that it can convert that energy more efficiently than conventional cars.

First big difference is the ICE. You may have read that it's unconventional in that the compression ratio is smaller than the expansion ratio. By allowing the burning fuel-air mixture to expand further, more of the energy is utilized. While this results in higher efficiency, the torque in this type of engine is rather low, and would not be acceptable to most people. However, this is compensated in the Prius with its high-torque electric motor.

The second advantage to having a battery is that all internal combustion engines work most efficiently at higher RPMs. In the Prius the ICE can operate at an efficiently high speed, and if there is excess power, it can be sent to the generator then into the battery for later use. One analogy that I heard was that a hybrid car is like a washing machine. You would never use a washing machine to just wash a pair of socks, you'd wait until you had a load of laundry to do. It's similar with a hybrid car; it can wait until the battery had run down and then run the engine at it's most efficient speed to charge the battery back up.

Finally, you're also right that regenerative braking doesn't generate that much power. However, how much braking energy is recovered in a conventional car? Another secondary benefit is that due to regenerative braking, the physical brakes in a Prius tend to last a lot longer than in a conventional car.

 

Hi Niepo,

Let me see if I can make the "Hybrid Car" concept concise. Otto cycle gasoline engines (most other cars on the road) have a "Partial Power Efficiency Problem". These engines must run stoiciometrically, that is the amount of fuel injected must match the amount of oxygen at a precise ratio. To limit power then, one must limit the number of molecules of oxygen that reach the cylinder. To do this, a throttle valve is used. It functions by causing lower air pressure behind it (towards the engine) then atmospheric pressure. So now the engine has to exert power to pull the air in past the throttle valve. This is wasted energy.

Additionally, there are aerodynamic issues with regards to the air-flow in and out of the cylinder. I have described this in a another post (http://priuschat.com/no-electric-for-pulse-and-glide-t20071.html). The short answer is that the engine has an optimum rpm/load point where effeciency is high. Typically for an Otto engines this is about .6 max power, at .8 max rpm. Which is kinda high, and if you operated at this engine point for very long the car would be doing 85 mph! Which would be very poor for vehicle efficiency (seperate from engine efficiency).

The idea to have a battery driven motor besides a gasoline engine is to permit using a smaller gasoline engine that has its peak efficiency point much closer to the average vehicle power requirement. Trains and 18 wheeled trucks are vehicles that have the engines matched to the average vehicle requirement, but without a hybrid drive. Needless to say, they do not accellerate at a modern day practical car requirement. The battery an motor allow for a smaller engine, and a normal acceleration.

After accelleration the engine can run at a higher, more efficient output level to keep the car moving at the cruise speed, AND charge the battery back up. Its the fact that the engine runs at the higher efficiency point that yeilds the hybrid fuel economy advantage.

Now the Prius is oh so much more than a hybrid car, with regards to fuel economy. It has the special Atkinson Cycle engine described by another poster (with the 13:1 expansion ratio, and normal compression ratio). It has the good aerodynamics. And it has the synergistically (with the hybrid drive) implemented CVT (which does not waste time shifting, alowing the engine to be even smaller for a given 0-60 goal). Of course regeneration helps too. And the way the Prius is implemented where it can cruise on battery power (increasing the recharge power even closer to the engine optimum efficiiency). And it turns the engine off at stops. All to avoid running the engine, when it does run, at low inefficient power levels. These things and the hybrid function make the Prius what it is.

 

<div class='quotetop'>QUOTE(donee @ Jun 11 2006, 05:22 AM) [snapback]269459[/snapback]</div>

Very nice indeed you omitted one small thing you forgot how well a diesel 18 wheeler goes up hill or how trains have to add 2,3,4 engines to climb over a pass. Imagine having to wait for 4 or 5 other Atkinson Cycles cars to join up to get over a pass? Folks in the West will relate. Parking at the chain install pull out until there enough of us to get over a pass? Pleeese

 

<div class='quotetop'>QUOTE(hdrygas @ Jun 12 2006, 10:41 PM) [snapback]270370[/snapback]</div>

I've had no problems traversing the rockies. Getting up and over Berthoud pass was no problem. Battery was tapped and the car had no problems.