RX 450 h reverse gear motors only no CVT

david foster · May 24, 2020

My ignorance!

Having owned my 2009 RX 450 for 3 years and having only once had difficulty emerging from mud IN REVERSE on Thursday last having been released from "lockdown" for angling I went to one of my favourite trout fisheries and reversed up a fairly slight incline on very dry grass to park. I was amazed at the noise made obviously from the motors and not the engine. I managed to park and thought no more about it, I was going fishing after all!

On getting home, I googled the issue and found that my suspicions were correct. The engine does not reverse, there is no reverse gear in CVT. I have lived with this ignorantly for 3 years but will be more aware in future and mention it in case others need to know.

Good to be back.

royoftherovers · May 24, 2020

Go on then Dave, I give up.

How does the car go backwards uphill without a reverse gear ?

steve2006 · May 24, 2020

Apparently John it has something to do with the sun, planets and maybe clutching at stars.

https://autoportal.com/articles/cvt-transmission-how-does-it-work-6660.html

NemesisUK · May 24, 2020

Just to clarify the e-cvt transmission in the RX (and all Lexus models) is not belt driven but it does use sun, planet and ring gears.

Gliderpilot · May 24, 2020

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.

ColinBarber · May 24, 2020

2 hours ago, david foster said:

The engine does not reverse, there is no reverse gear in CVT. I have lived with this ignorantly for 3 years but will be more aware in future and mention it in case others need to know.

Why is there a need to know? You have electric motors driving front and rear wheels on the RX so you have better traction than using the IC engine which can only drive the front wheels.

When reversing the IC engine may run, as if there isn't sufficient capacity in the hybrid Battery the engine is used to turn the generator which supplies the electricity for the motors.

If you were getting wheel spin then the noise is probably the traction control stopping/starting. It isn't good for the transmission to run unloaded so the hybrids have an aggressive traction control, in either forward or reverse.

royoftherovers · May 24, 2020

3 hours ago, steve2006 said:

Apparently John it has something to do with the sun, planets and maybe clutching at stars.

https://autoportal.com/articles/cvt-transmission-how-does-it-work-6660.html

Thanks Steve and for the link.

By Jupiter and the 82 moons of Saturn, its all about inter- planetary travel.

There is no reverse gear because there is no forward gear and what is not there cannot go wrong !

Britprius · May 24, 2020

One of the real anomalies of the hybrid system is that if the engine does run while reversing it actually fights against the electric motors driving the car backwards reducing the available reverse power.
If you need to reverse up a steep slope and the hybrid Battery is low on power it is better to force charge the Battery. Putting the car in "D" holding it with the foot brake, and revving the engine until the Battery has a reasonable level of charge. Then reverse up the slope.
It is not unknown for the Prius/CT200h to refuse to move up a steep slope in reverse with the engine running. What other Toyota/Lexus hybrid vehicles are affected as much I do not know, but I suspect most are.

John.

Richard Fixter · May 25, 2020

I remember seeing one of these gear boxes put together as a cut away behind a Perspex screen at Burnaston when I worked there absolutely amazing tech.

Barry14UK · May 25, 2020

So trying to reverse up Porlock not a good idea then!

JBPRX400h · May 26, 2020

Hah! Memories of my first vehicle back in 1969. A Ford Thames 15cwt van. It was unusual in that it had a 4 speed gearbox. However it would not stay in first gear and would just drop out under load.

One weekend in the early seventies we decided to drive from Ambleside up to the Kirkstone Inn, a narrow little road with several 1 in 4 hills. All went well until we reached the final steep bit and the poor old van just couldn't make it in 2nd gear so we turned round in a gateway and stormed up the last ascent in reverse. Only trouble with that was it was (for the Lake District) a hot sunny day so the engine overheated and we arrived in the carpark opposite the inn in a great cloud of steam and to a round of cheering and applause from the customers sitting outside in the sunshine!!!

Happy days!

JBP

Thackeray · May 26, 2020

On 5/24/2020 at 8:36 PM, royoftherovers said:

Thanks Steve and for the link.

By Jupiter and the 82 moons of Saturn, its all about inter- planetary travel.

There is no reverse gear because there is no forward gear and what is not there cannot go wrong !

I've come to the conclusion that some of my past confusion about how this works is because I've tended to look at Lexus hybrid cars as petrol-engined cars assisted by electric motors.

I've now realised that it makes more sense to look at them as electric cars, which are sometimes (but not always) assisted by a petrol engine. What this means is that for the car to move (unless you're coasting) at least one of the motors must be powered and generally the motor generator attached to the road wheels (MG2) must be powered to get moving. As has been pointed out, to reverse the car, the computers simply run MG2 backwards.

Toyota does make some conventional belt driven cvt gearboxes. The link mentioned describes this kind of gearbox, not the hybrid planetary gear Power Split Device or e-CVT.

So I don't think it hurts to link, once again, to the following very useful simulation of the planetary gearset. Many thanks to the person who created this on the eahart.com website. Unfortunately, this is going to stop working soon as Adobe Flash is withdrawn. Hopefully, someone might convert it into something more modern - I believe HTML5 may be an option for anyone who understands these things.

http://eahart.com/flash/PSDAnim.swf

http://eahart.com/prius/psd/

royoftherovers · May 26, 2020

1 hour ago, JBPRX400h said:

Hah! Memories of my first vehicle back in 1969. A Ford Thames 15cwt van. It was unusual in that it had a 4 speed gearbox. However it would not stay in first gear and would just drop out under load.

One weekend in the early seventies we decided to drive from Ambleside up to the Kirkstone Inn, a narrow little road with several 1 in 4 hills. All went well until we reached the final steep bit and the poor old van just couldn't make it in 2nd gear so we turned round in a gateway and stormed up the last ascent in reverse. Only trouble with that was it was (for the Lake District) a hot sunny day so the engine overheated and we arrived in the carpark opposite the inn in a great cloud of steam and to a round of cheering and applause from the customers sitting outside in the sunshine!!!

Happy days!

JBP

And in `65, my old 1948 Split Screen Side Valve 848cc Minor would huff and puff its way up the long hill out of St Asaph in 1st gear with all passengers pedaling like fury !

niko79 · April 17, 2021

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?

Herbie · April 17, 2021

1 hour ago, niko79 said:

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?

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?

serbarry · April 17, 2021

2 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?

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?

Deathstar · April 17, 2021

Is there a limit to what the RX450h can reverse up? Will it just display a warning or refuse to move?

Herbie · April 17, 2021

1 hour 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?

In the RX there's a 'shift lock' button that you can press to move the shift lever.

niko79 · April 18, 2021

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?

niko79 · April 18, 2021

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.

Thackeray · April 18, 2021

12 hours ago, niko79 said:

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?

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.

niko79 · April 18, 2021

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?

Thackeray · April 19, 2021

14 hours ago, niko79 said:

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?

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.

niko79 · April 19, 2021

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!