Why does the gas motor come on so soon?

[Katznbooks]

New here. Got my RED 06 in September, just found this board last night.

I'm curious why the gas engine kicks in as I start to take off very slowly, or even if I sit and idle for 5 or 10 seconds.

[Marlin]

<div class='quotetop'>QUOTE(Katz @ Nov 15 2006, 10:01 PM) [snapback]349872[/snapback]</div>

New here. Got my RED 06 in September, just found this board last night.

I'm curious why the gas engine kicks in as I start to take off very slowly, or even if I sit and idle for 5 or 10 seconds.
[/b]

My assumption has always been that it does that to make sure it can start the engine. It would rather suck to get a mile or two away, have the battery run out, and then find out the engine won't start.

[donee]

<div class='quotetop'>QUOTE(Katz @ Nov 15 2006, 10:01 PM) [snapback]349872[/snapback]</div>

New here. Got my RED 06 in September, just found this board last night.

I'm curious why the gas engine kicks in as I start to take off very slowly, or even if I sit and idle for 5 or 10 seconds.
[/b]

Hi Katz,

The engine comes on fast, because all the electricity in the battery is generated by the engine, and the electric acceleration is about 66 percent efficient. So, the total efficiency from fuel to accelleration is worse by electric means, than by engine. The efficiency tank to wheel for engine is Engine Efficiency * Transmission Eficiency * Final Drive Efficiency. The electric efficiency tank to wheel is Engine Efficiency * Transmission Efficiency * Generator Efficiency * Electric Drive Efficiency * Motor Efficiency * Final Drive Efficiency. Or Electric Efficiency = Tank-to-Wheel Efficiency * Generator Efficiency * Electric Drive Efficiency * Motor Efficiency . Since the Generator to Motor loop is about 54 percent efficient, its best to put the engine output directly through the transmission to the final drive whenever the requirement puts the engine into an efficient level. Accellerating takes allot of power, and the engine will be in efficient output level during that requirement.


The Hybrid advantage comes along at cruise when the power required is way to low for the engine to run efficiently. This is typically 25 to 40 mph in the Prius, but more like 25 to 60 mph in an Otto engine car, because of the lower part throttle efficiency. In this speed range its easy to drop into glide (no arrows) , or use the electric drive.

The electricity comes from regeneration, and the output requirement is low but too much for the battery alone - then the system runs the engine power to both the battery and the wheels. This increases the engine power output into a more efficient level.

This is the kinda the 2-bit technology basis for the Hybrid car. Hope it was a good answer to your question.

For good mileage it best to avoid electric acceleration unless, its very low accelleration, or the battery is up in the green-bars level. If the battery is up in the green level, the car is going use the battery anyway to get the level down. Preserving battery charge for cruise is best, because the current levels are lower in the interconnects, motor and motor drive, which disipates less heat, and gets better distance per KWH.

[mojo]

I thought the ICE started for the first few minutes, only to preheat the Catalytic Converter.

[Fibb222]

<div class='quotetop'>QUOTE(mojo @ Nov 15 2006, 06:08 PM) [snapback]349898[/snapback]</div>

I thought the ICE started for the first few minutes, only to preheat the Catalytic Converter.
[/b]

I agree with mojo, that the computer 'decides' to turn the engine on soon aftwer power-up mostly to warm itself and the especially to warm up the catalytic converter so that the emmissions are as low as possible.

Also, even if the ICE and catalytic converter are warmed up nicely, the engine might decide to come on when you are stationary if you have the heater or A/C on and/or if the 200 Volt battery is low.

Cheers

[Marlin]

<div class='quotetop'>QUOTE(Fibb222 @ Nov 15 2006, 11:15 PM) [snapback]349899[/snapback]</div>

I agree with mojo, that the computer 'decides' to turn the engine on soon aftwer power-up mostly to warm itself and the especially to warm up the catalytic converter so that the emmissions are as low as possible.

Also, even if the ICE and catalytic converter are warmed up nicely, the engine might decide to come on when you are stationary if you have the heater or A/C on and/or if the 200 Volt battery is low.

Cheers
[/b]

Except that if you just sit there in the parking space, the engine starts 7 seconds after you turn the car on and runs for about 30 seconds and then shuts off again. I doubt it did much warming up of anything in 30 seconds, at least not to anything resembling normal operating temperatures.

So why not wait until power from the engine is actually needed before starting the engine. That was in essense the question of the original poster.

[jtmhog]

<div class='quotetop'>QUOTE(Marlin @ Nov 16 2006, 07:59 AM) [snapback]350063[/snapback]</div>

Except that if you just sit there in the parking space, the engine starts 7 seconds after you turn the car on and runs for about 30 seconds and then shuts off again. I doubt it did much warming up of anything in 30 seconds, at least not to anything resembling normal operating temperatures.

So why not wait until power from the engine is actually needed before starting the engine. That was in essense the question of the original poster.
[/b]

You're right about normal operating temperature of the engine which is reflected in the temperature of the engine coolant. However, the cat converter is heated by the exhaust gas which is much hotter than the coolant and can raise the temperature of the cat converter in a matter of seconds and not minutes.

[qbee42]

<div class='quotetop'>QUOTE(Marlin @ Nov 16 2006, 08:59 AM) [snapback]350063[/snapback]</div>

Except that if you just sit there in the parking space, the engine starts 7 seconds after you turn the car on and runs for about 30 seconds and then shuts off again. I doubt it did much warming up of anything in 30 seconds, at least not to anything resembling normal operating temperatures.

So why not wait until power from the engine is actually needed before starting the engine. That was in essense the question of the original poster.
[/b]

It's warming up the catalytic converter. The first priority for the Prius is low emissions. Fuel economy comes second.

Tom

[eagle33199]

<div class='quotetop'>QUOTE(donee @ Nov 15 2006, 08:00 PM) [snapback]349894[/snapback]</div>

Hi Katz,

The engine comes on fast, because all the electricity in the battery is generated by the engine, and the electric acceleration is about 66 percent efficient. So, the total efficiency from fuel to accelleration is worse by electric means, than by engine. The efficiency tank to wheel for engine is Engine Efficiency * Transmission Eficiency * Final Drive Efficiency. The electric efficiency tank to wheel is Engine Efficiency * Transmission Efficiency * Generator Efficiency * Electric Drive Efficiency * Motor Efficiency * Final Drive Efficiency. Or Electric Efficiency = Tank-to-Wheel Efficiency * Generator Efficiency * Electric Drive Efficiency * Motor Efficiency . Since the Generator to Motor loop is about 54 percent efficient, its best to put the engine output directly through the transmission to the final drive whenever the requirement puts the engine into an efficient level. Accellerating takes allot of power, and the engine will be in efficient output level during that requirement.
The Hybrid advantage comes along at cruise when the power required is way to low for the engine to run efficiently. This is typically 25 to 40 mph in the Prius, but more like 25 to 60 mph in an Otto engine car, because of the lower part throttle efficiency. In this speed range its easy to drop into glide (no arrows) , or use the electric drive.

The electricity comes from regeneration, and the output requirement is low but too much for the battery alone - then the system runs the engine power to both the battery and the wheels. This increases the engine power output into a more efficient level.

This is the kinda the 2-bit technology basis for the Hybrid car. Hope it was a good answer to your question.

For good mileage it best to avoid electric acceleration unless, its very low accelleration, or the battery is up in the green-bars level. If the battery is up in the green level, the car is going use the battery anyway to get the level down. Preserving battery charge for cruise is best, because the current levels are lower in the interconnects, motor and motor drive, which disipates less heat, and gets better distance per KWH.
[/b]

First, all the electricity in the batteries is not generated by the engine. Some of it is, but some of it also comes from the regenerative braking. How much of each is highly dependent on the individual driving style.

As for the hybrid advantage, it once again is much more complex than that. First advantage: the ICE stops running when it doesn't need to. Second advantage: Electric power for acceleration assistance. Third advantage: recapturing of lost kinetic energy through regenerative braking. It's a combination of these and many, many more factors that make the car run so well.

As far as preserving battery charge for cruise... using it for gliding is much better. The most efficient way to drive the car is to "Pulse" up to speed (using the ICE, with a little regen to the batteries) then "Glide" down a bit (ie with no arrows on the energy display). Unfortunately the glide portion does use a little electricity, thus you need a little bit of regen when pulsing.

As far as cruising (I assume you're referring to highway speeds) - the battery SOC doesn't change much when you're at speed. in fact, if you find a perfectly flat section of road and are cruising along at 65, you probably won't see much, if any, action going on with the batteries. When i'm at 6 bars and on the highway, generally it'll either just be all ICE (at very low RPM's giving good mileage) or the battery will be constantly flip flopping between providing and storing power.

As for the OP:
The ICE does start up 7-8 seconds after you start the car, every time. this is in order to heat up the catalytic converter and the coolant. You should also find the guide on here for the 5 stages of Prius operation - it discusses the details behind warming up and progressing through the stages to the point where the ICE can turn on and off at any time. (as opposed to just turning off after you've come to a complete stop, like it does in earlier stages)

[qbee42]

<div class='quotetop'>QUOTE(eagle33199 @ Nov 16 2006, 10:38 AM) [snapback]350096[/snapback]</div>

First, all the electricity in the batteries is not generated by the engine. Some of it is, but some of it also comes from the regenerative braking. How much of each is highly dependent on the individual driving style.
[/b]

Unless you push your Prius up a hill before you start, all of the electricity in the battery comes from the ICE. The electricity generated by regen braking is converted from kinetic energy that was imparted by the ICE; all of the energy comes from the ICE. It takes many paths getting to the road, buy it all comes from the ICE. It can go directly to the road through the PSD; through MG1 to MG2; stored in the battery and later through MG2; or stored as kinetic energy in the Prius, then to the battery through regen, then back through MG2. Regardless, it all starts as gasoline burned in the ICE.

Tom