IS300h cvt gearbox

[bernieeccles]

Right, I know that the E CVT is a planetary gear system as opposed to the belt and cone type but one thing I cannot find the answer to is this.

How does the engine take up the drive from a standstill ?

A manual transmission has a clutch which will slip to provide a smooth take up of engine power.

A conventional auto has a fluid coupling i.e. a torque converter.

What does the Lexus E CVT have ?

[C Mclean]

Electricity produced by the engine and from the Battery powers the motor the turns the wheels. Simplified explanation from a numpty..

[OldTrout]

Bernie,

You may find this explanation and simulator helpful http://eahart.com/prius/psd/

John

[NemesisUK]

Pretty good video here

 

 

[OldTrout]

And if you want to read rather than watch then Wikipedia is good and detailed https://en.wikipedia.org/wiki/Hybrid_Synergy_Drive

[NemesisUK]

Another good on, in which the presenter mentions the clutch damper assembly that mounts between the power split device and the engine. 

So to answer the OP's question, there is a clutch assembly that takes up the drive from the engine

 

[bernieeccles]

Thanks for those replies and the videos, they explain it quite well, but I have a question.

If the Hybrid Battery was not functioning, say the isolating plug was out, could the IC engine actually drive the car from a standing start with a smooth pull away or is that the function of the motor/generator so having no power, the car would not move ?

[NemesisUK]

My handbook states that without traction Battery power the car will not move, it cannot function on petrol only.

[bernieeccles]

I think I've got it, so I assume when the car comes to a stop on a hill, the electric motor must have to spin to hold the weight of the car from rolling backwards, a bit like holding a manual transmission car on the clutch. Or in that situation, does the IC engine always fire up ?

[NemesisUK]

No, my car will hold on a hill without the engine starting. The hill start assist function holds the car for a maximum of 2sec after the brake pedal is released, seems longer though.

[bernieeccles]

How does it do that ?

[NemesisUK]

Presumably It uses the electric motor. 

From the handbook

Operating conditions of hill-start assist control
When the following four conditions are met, the hill-start assist control will operate:
● The shift lever is in a position other than P or N (when starting off forward/backward on
an upward incline).
● The vehicle is stopped.
● The accelerator pedal is not depressed.
● The parking brake is not engaged.
■ Automatic system cancelation of hill-start assist control
The hill-start assist control will turn off in any of the following situations:
● The shift lever is moved to P or N.
● The accelerator pedal is depressed.
● The parking brake is engaged.
● Approximately 2 seconds elapse after the brake pedal is released

[NemesisUK]

Actually thinking more on this, it would be the electronically controlled baking system that holds the car on a slope by locking the brakes on. One of the advantages of having a brake system pressurised by an electric pump rather than the normal vacuum servo assisted systems.

[PaulWhitt20]

I thought it would hold for more than two seconds. Sometimes when stopped on a hill I can stay stationary without the parking brake or foot brake depressed.

Perhaps in the situation the creep forward is equal to the roll back.

I thought it could not roll back.

Like how the include electronically controlled baking these days. Never know when you may need a cake.

[NemesisUK]

16 minutes ago, PaulWhitt20 said:

Like how the include electronically controlled baking these days. Never know when you may need a cake.

LOL ... 

My mind is on the bread I have currently in the oven, Mmmmm 

[bernieeccles]

I suppose that  we should just  accept that "it works" but I've always been the type of person that loves to pull things apart to see how they work. 

I always have in mind, that if something (like the clutches in DSG type boxes) can wear out they will and will have the associated cost of replacement. Of course for lots of people who move their cars on every few years, that won't matter, but for those who tend to keep cars for longer, it is always something to consider.

So, just to recap on the IS300h, no friction clutch to wear out, aside from the damper which does look like a clutch plate.

All in all, very clever stuff !

 

[Britprius]

The clutch damper is only a method of removing shock loads from the transmission. There is no mechanism to release "open" the clutch. It is designed to slip only when shock loads are applies to it, and as such should outlast the life of the car.

The car holds on a hill by power being applied to MG2 (Motor generator 2) the larger of the 2 motors connected directly to the transmission output, and so the wheels. This is enough power to hold the car without the MG2 turning.

John

[OldTrout]

5 hours ago, bernieeccles said:

I suppose that  we should just  accept that "it works" but I've always been the type of person that loves to pull things apart to see how they work. 

......

All in all, very clever stuff !

 

I too have always been curious about how things work. The Toyota HSD has a lot of stuff to be curious about. I've given up on anything except basic understanding and accept that it works and works very well too. The throttle response on my Mk3 GS450h  is so much better/smoother than it was on my Mk2 GS300. Two years in I'm still enjoying driving it.

John

 

 

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[darrude]

It's not really a gearbox as such, it's a differential used in reverse.  IE, rather than splitting power to multiple shafts, takes multiple inputs to output to a single shaft.  meaning that power and speed output is determined by the 2 input speeds.

IE:

Engine spins at 5000 rpm, electric spins 5000 rpm, shaft spins 10,000 RPM 

Engine spins at 5000 rpm, electric spins in reverse @ 5000 rpm, shaft spins at 0 RPM 

I've just made up the values for an example, no idea what ratios and gearing is used between the drive trains, but just trying to find a simple explanation.  

A very clever simple solution though.