niko79

2 hours ago, Thackeray said:

Yes, that's right. As Britprius says above, if you have the engine running while reversing it is pushing the car in the opposite direction to the electric motor. If you add the force of gravity while trying to reverse up a hill then the electric motor has to work even harder. But I imagine the Prius MG2 motor is smaller than in the RX 450h so the chances of an RX 450h not being able to get up a hill are probably not very great.

Thank you!

6 hours ago, Thackeray said:

That's easy to visualise. Nothing happens!

That's to say nothing mechanical happens. In fact nothing happens in the transmission when you select any gear except Park. That's because the planetary gearset has permanently engaged cog wheels that are never disengaged. I don't know what the RX gear selector is like but if it's a substantial chunky one, like in the IS, that's just for show and to make it seem like a conventional automatic gear selector. If you've seen the Prius gear selector, you'll have seen how insubstantial it is and this performs exactly the same function.

When you select Park, the transmission is locked with a parking pawl and this might be operated mechanically by the gear selector or it might be engaged electronically as on some Toyotas. I don't know which it is. But the other gear position selections do nothing mechanically.

Normally, when you put the selector in Reverse, MG2 which drives the road wheels is put into reverse. I suppose this is by reversing the electric current but maybe someone who knows about electrics will correct me if that's wrong.  But nothing happens mechanically.

But if the 12v battery is dead, the high voltage battery remains isolated and doesn't provide any power to the electric motors. So what happens if you push the car backwards?

You do need to take it out of Park to release the parking pawl otherwise the car won't move but if there's no electricity I can't imagine that it makes any diffference which "gear" you select. My instinct would be to select Neutral but I don't suppose it makes any difference if there's no power.

Then after taking it out of Park, when you start to push the car backwards, MG2 rotates backwards. In the planetary gearset MG2 is attached to the outer ring gear which tries to push round the planets, which are attached to the engine. But the resistance of the engine will probably be enough for the engine not to turn. So the turning force will be passed on to the inner sun gear, which is attached to MG1.  This motor-generator is free to spin because there's no electric power being fed to it or drawn from it. So if you don't push the car too fast, the engine will probably not spin backwards and all the turning motion will be passed on to MG1 which will spin freely.

But personally I wouldn't risk doing this at any speed. There might come a point where the engine could start to turn backwards (and maybe that isn't a problem - I don't know). And spinning MG1 too fast for any length of time might not do it any good. This is all hypothetical, of course, because in practice you probably aren't going to push the car backwards for more than a few feet very slowly.

Thank you, Thackeray for the insight! 

Would this situation above be similar to trying to back up in a steep hill while the gravity force drags the car down the hill? Which im pretty sure has happened to many of us?

3 hours ago, serbarry said:

But if the battery had died, he could not start the car and consequently he could not put in neutral. At least in the Prius it is not possible but maybe the RX is different?

Well, there is a litle plastic cover in the panel (RX 450h at least) that will expose a recess area. When you press that, it allows you to force the gear into another mode i.e. neutral, reverse etc. 

6 hours ago, Herbie said:

I'm sure that for just a few feet then yes, that should be alright. However, why didn't they (or you) just put it into Neutral and physically push it back a few feet?

Thank you. Yea, that is what bothered me at that time but did not want to make a big deal out of it.. They also thought the electric parking brake was still ON, and with a dead Battery you cant really tell.

Im trying to visualize what happens when gear is put into reverse, and you push the car back? Shouldn't this naturally align with the way the transmission is locked in R mode AND would not have been a problem at all even if the car was pushed back for a longer distance?

On 5/24/2020 at 12:21 PM, Gliderpilot said:

All Toyota Lexus hybrid vehicles do not have a mechanical reverse gear, the direction of the electric motor or motors are reversed to go backwards. None of the CVT gearboxes use belts and variable cone pulleys to change the gear ratios. The front transmission unit has two electric motors, one directly connected to the drive wheels and another connected to an epicyclic gear train and has two functions, 1 to start the engine and 2 to vary the ratio of power between the engine and electric motor. There are some very good videos on YouTube which explain this better than I can.

Excuse my ignorance. Given there is no mechanical reverse gear, what does shifting into "R" do exactly?

I ask the question because recently ran into this situation. Had parked nose in into a parking garage. Battery had died a couple of months later. Then I could not jumpstart it because some pipe would not let me open up the hood. Had to call roadside assistance; they came in and BEFORE they lifted the rear wheels and tow the car a few feet back, they SHIFTED the gear into reverse first for some reason. I was worried that this might have caused some harm somewhere.

However, reading your post, it seems shifting into reverse before towing the car backwards for a few feet should have been fine? Is that correct?