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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.

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Go on then Dave, I give up.

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

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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.

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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.

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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.

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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 !

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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.

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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.

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

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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

 

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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/

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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 !

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