[JPeterman]

why does the Prius draw power from the wheels when I take my foot of the gas? Wouldn’t it be more fuel efficient to let me coast?

And related to this question, my commute has a few miles of perfect coasting road. Sometimes I force the car to coast by shifting into neutral. Is the car still able to use the ICE to charge the batteries in neutral? My coasting segment is very near work so the ICE tends to run while I coast to warm up and minimize emissions. I’m suspicious that my shift into neutral might be hurting me more than helping me if the ICE’s energy is lost during warm up.

 

[Canadian Prius]

While coasting the prius simulates mild engine braking by drawing energy from the generator. This has the effect of charging the battery while giving the car the 'feel' of other cars.

If you want to coast without this effect, you can put up the energy screen and watch as you apply a little throttle. The green arrows going from the wheels to the generator to the battery will disappear at a given point and if you press a little harder, the orange arrows will go from the battery to the motor to the wheels. That interim place with no arrows is simple coasting. With a little practice you can get it any time you want it.

 

[ehurtley]

As CAPo said, just apply a little pressure to the accelerator. It appears to be an attempt to simulate an old-fashioned automatic transmission, gas engine car. I'm assuming this is the same reasoning behind why, when stopped, it applies electric power if you don't press the brake pedal down, to simulate the power of an automatic transmission/gas car at idle. I would like it if both 'features' could be disabled through some button voodoo. I'm used to a manual transmission, so both functions feel wrong to me. I suppose to someone used to automatics, it 'feels right', but not to me.

 

[mikepaul]

I never thought of 'just coasting', since any energy collected would go towards saving me some gas later. Perhaps I'm just cheap...

 

[richard schumacher]

It's a tough call; there's no one strategy that is optimal in all situations so Toyota built it to behave reasonably on average, and to mimic the familiar slowdown of a conventional automatic transmission. Sometimes a modest amount of regenerative slowing will reduce the amount of friction braking needed later, and that will save energy. But regeneration is not very efficient, so doing it all the time does waste energy that in some circumstances would not have to be wasted (for example, going down a very gentle slope with no stop in the forseeable future). Practicing how to "feather" the accelerator so that it does truly coast (with no regeneration) can help.

 

[mrv]

Neutral is just that - neutral.
Neither your gas engine nor the electric motor can propel you car.
You get no regenerative braking.
The gas engine cannot charge the HV battery.

Try putting it in neutral and compare the braking feel to when you're in Drive. You'll have to push harder on the brake pedal for the hydrolic brakes to do what the regenerative braking would normally help with. Press on the accelerator pedal and hear the gas engine roar, but do nothing.

On the classic Prius, it is all too easy to nudge the gear shift from Drive to Neutral while driving. Reach for the Audio button to change the volume, hit a bump in the road, and your arm pushes the gear shift lever from D to N without you realizing it. You're suddenly loosing power, pressing on the accelerator doesn't speed up your car but the engine RPMs go up, and it's more difficult to brake. Very scary, until you realize that you're in N...


You're really better off to just coast in D, recharging the battery, than going into Neutral where you'll loose all that extra energy. About the only use for N is for going through car washes or being towed...

 

[AgentElrond]

I've also managed to find the "just coasting" spot using the Energy screen. Generally, if I'm actually intending to decelerate, I'll lift my foot a bit more to engage engine braking and at least try and get *something* out of it.

 

[mdacmeis]

why does the Prius draw power from the wheels when I take my foot of the gas? Wouldn’t it be more fuel efficient to let me coast?

This is not an efficiency issue, but more of a driveability issue. There are two fundamental reasons for this type of reaction from an engineer's perspective. First, historically, engines have provided some amount of deceleration, or engine braking, when the throttle is closed. Most drivers want this continued, and certain vehicles which have deviated from this have had high rates of warranty claims. Always having to apply the brakes to adjust your speed in traffic, as one particular GM engine is notorious for, has not been viewed as a positive "feature." Second, the throttle is not intended to be an on/off switch. Most expect a linear progression of increased power as the throttle is increased. When the throttle is off, drag and friction should slowly decelerate the vehicle to its idle state. When the throttle is opened, power is progressively increased until the losses are overcome and positive torque is achieved.

What you have to consider is would you really want to default to coast every time the throttle is at 0%? If you think about it, and how often you would then need to apply the brake to maintain a desired distance from other vehicles, you will quickly realize this does not work for most people. For most, engine braking is expected. The debate among powertrain engineers is how much engine braking should there be under given conditions, as the amount can be adjusted using calibrations during development.

 

[BIF]

I've also managed to find the "just coasting" spot using the Energy screen. Generally, if I'm actually intending to decelerate, I'll lift my foot a bit more to engage engine braking and at least try and get *something* out of it.

I too, can coast. Depending on road and wind conditions, you can coast and lose speed not at all, very slowly, or more rapidly.

It's kind of a "sweet spot" in the pedal, similar to "stealth." Sometimes, I will coast toward a red light if I don't want to step on the brake or encourage somebody from cutting me off. Coasting in is "free."