Is it ok to reverse and put in drive while its reversing?

up to a couple mph, sure

 

no, there's no mechanical linkage

 

The car doesn't mind a bit. You're just reversing the torque on an electric motor; it will smoothly slow you in the direction you were going and continue to accelerate you the other way. Same for shifting from D to R.

Above a certain speed, 6 or 7 MPH, the car will instead double-beep and shift to neutral. That doesn't harm the car either, and it isn't even done because the shift would be harmful to the car, but more because at higher speeds it makes sense to wonder if it's what you really intended.

 

then i wouldn't do it

 

I've done it occasionally, just around 1~2 mph as @bisco says, but I try not to.

 

I've never noticed that when I do it. Maybe there's some other issue with your car.

 

At slow speeds regen is disabled and friction brakes are used, but if you shift from R to D when moving, then motors are essentially doing just that, regen at very slow speed. Don't know if it does any harm but that is the fact.

 

I imagine that the gas engine starting-while-rolling-backwards reduces the starting impulse somewhat. If there’s an additional factor (old spark plugs, dirty throttle body etc) that could make for a shaky engine start, maybe you just found a way to expose that symptom a little earlier than usual.

 

There is a difference, either subtle or glaring depending on how you look at it.

During regen braking, the M/G is acting as a generator. It resists the motion and slows the car because it is converting the car's momentum into electrical energy to be stored in the battery.

When you switch from R to D, the M/G is acting as a motor. Electrical energy is being fed into it (in the "go forward" direction), causing it to first slow the car's reverse motion, then accelerate it forward.

The friction brakes take over from regen at slow speeds because the amount of power the generator can put out depends on speed, and is piddly down at 1 or 2 MPH, so it can neither recapture much energy nor slow the car much.

Of course there's no such limitation when the car is pouring energy into the motor; indeed, the high torque available from the electric motor at low speed has for years been the thing that's always talked about even by people who hate everything else about hybrids.

 

regen efficiency is dialed in really well in the Prime. But there are limits of speed to efficiency at both hi and low speeds. Obvious?

 

I've tried to make myself come to a full stop. This is the first automatic ive owned in my life so it's taking some getting used to.

I can't imagine it's good to shift into D while rolling backwards. At best, it does nothing, but I err on the side of caution and just stop.

That said, I did it all the time in the other cars ive owned (manuals) and never had to replace a transmission

 

I also sometimes do it at the same very low speeds as on manual transmissions, which still make up 2/3rds of my household's stable. Of course it means slightly more clutch wear on the MTs, but when the speed is very small, so is that extra wear. And we also have never had to replace a transmission or clutch. Even on the spouse's daily driver, which I bought new for her just over 30 years ago. Though it is only just closing in on 200k miles, not a household distance record.

 

Compared to the transmissions in other cars, the one in the Prius contains literally nothing subject to damage from doing that.

 

I seem to recall an earlier discussion about this. Somebody actually tried it at various speeds. It worked up to a limit, and above that the car just went into neutral. There aren't any gears changing, only power to electric motors.