The electric motors respond nearly instantly compared to the ICE. Measurements indicate that in ordinary driving, the ICE start takes about 250 ms. However, the ICE does operate over a range from as low as ~1,000 rpm, idle and coming to a stop, up to 4,500 rpm in the NHW20, full power.

There is an engine rpm range where the ICE is producing power at peak efficiency, from 1,200-2,400 (measured with my NHW11.) As the rpm goes higher, I'm seeing a decrease in specific fuel efficiency that really becomes noticeable above 3,200. But sometimes, the power is needed.

The problem is the catalytic converter needs to be at several 100s C. These are 'oven' temperatures and the exhaust gas is very effective. Fortunately, the catalytic warm-up is fairly brief compared to getting the block warmed. We have a lot of data about the effectiveness of block heating and some of us are experimenting with a thermistor hack. BTW, Ken provided key data from Japan needed for the latest set of experiments and Clive Burk in the UK first suggested one approach.

Bob Wilson

 

As I understand it, that is because the engine was undersized (for efficiency) and the atkinson cycle. Both reduce the ability of the engine to provide immediate torque. The electric motors are used to compensate. Thats part of the beauty of hybrids. Normal vehicles lug around larger engines than they need to. They only need the extra power to accelerate and to get moving. When cruising at constant speed you are just lugging around alot of extra metal you don't need.

 

I see, so the electric motor is really just kicking in to avoid the impression of "lag" on pressing the accellerator. So it sounds like pressing the accellerator gradually would make some impact on MPG - you avoid using the electric motor as much to cover lag. If you press it below a certain rate when the ICE is running do you avoid using the electric motor completely (avoid it kicking in to hide lag)?

Would an engine block heater and a cat heater make sense? 350C is amazingly hot though - I wonder what the electricity cost would be to get an electrical resistor that hot? As a big metal box though you'd only need the resistor that hot very briefly as it would conduct into the cat pretty effectively.

 

Yes I think the lag description is accurate.

Theres an interaction, but its kinda hard to put a finger on it... the push from the electric motor is often supplied by the battery, which might have been recharged by regen (in which case the energy is "free" ie you would have lost it in braking and you've recaptured it) there is also some direct recharge of the battery on most of these things, in which case there is a direct MPG relationship.

I think if you hit it too hard it wil cost you and if you baby it too much it will cost you as well.

I can't say for a Prius, but for an FEH a CAT heater isn't useful since the CAT temperature seems to be inferred from the coolant temp (no temp sensor in the CAT). An engine block heater can get you into EV mode on an Escape faster so I'd assume thats also true of a Prius.

 

Ah... I see. So heating the engine block has the indirect effect of causing the CPU to assume the cat converter is ready to go as well... when in fact it may very well not be. The gas savings is more because you're gaming the CPU than because everything is really ready to go.

 

The catalytic converter temperatures are detected by the O(2) sensor voltages, not the coolant temperatures. Until the O(2) sensors get hot enough to generate a mixture voltage, the catalytic converters are 'too cool.'

There are direct and indirect effects of the coolant temperature. It turns out that 'spoofing' the coolant temperature modifies the 2001-2003 Prius control laws so it behaves more like the current model. But it can't fool the oil viscosity. So if you spoof a warmer coolant temperature too soon, the ICE will stall . . . like a regular engine.

Bob Wilson

 

On the Escape, from part of a manual someone posted, the O2 sensors are heated with and integral heater so they can generate an accurate mixture measurement in a few seconds of startup and provide mixture control immediately.... so on the Escape the O2 sensors wouldn't give CAT temp.

I know nothing about the Prius O2 sensors, so in that case you likely know more than I do.