Protecting your turbo - turning off the hybrid engine

[tacorancher]

If you are coming off the highway or hill climbing, DRIVE IT EASY for about a mile. Just keep the rpm’s up slightly and it will not go into hybrid mode. My understanding is that there is not a way to shut off the hybrid. Just don’t drive it in stop and go traffic or where there are stoplights if you are trying to cool the turbo. Not really hard to understand and your owners manual is a great resource.

That answer is both condescending and not really very good. It assumes that the Toyota engineers didn’t consider a way to let the turbos cool in the hybrid version—that they just said “fuck it, we need the engine to shut off in hybrid mode and to hell with the turbos—hopefully folks will just run the engine gently after high load and not let the engine shut off in hybrid mode”. Of course I could always follow that protocol which assumes that we have to find a way to let the turbos cool without the truck automatically shutting off the engine. But I find that answer to be ridiculous. What I’m curious about is how the engineers sorted this issue. Thanks for pointing me to the manual… lol. These kinds of answers are so obnoxious.

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[NCEngineer]

@JustAnotherDingus No, there is no way to alter the stop/start in any 4th gen hybrid, even with a Carista. When the engine runs and when it shuts off is strictly under the control of the hybrid system.

When I let off the gas and coast to a stop the ICE shuts off immediately. As I am slowing down it uses regen to charge the traction battery. If I am just creeping forward it will remain off, but as soon as I give it much accelerator input it starts up again.

The first time I was stuck in a long line of stop and go traffic it would shut off at each stop and start backup when traffic moved. But after about 10 minutes of that it no longer shut off, probably because the battery was getting low. Then later it began shutting off again when the battery had recharged. It is much more complex and sophisticated than I expected.

It is so smooth and so seamless that I have stopped paying much attention to it and I just let Toyota's hybrid magic sort it all out.

You actually can force it to not turn off at idle. Turn on Tow/haul mode and it won’t shut off the ICE. Not saying you should do that. Just saying that’s one thing Tow/haul mode does.

 

[TacoFreak]

You actually can force it to not turn off at idle. Turn on Tow/haul mode and it won’t shut off the ICE. Not saying you should do that. Just saying that’s one thing Tow/haul mode does.

Thanks for that info - I did not know that. It isn't something that I would do on a regular basis but it makes sense when towing or hauling. It is just another sign that Toyota has this figured out with the hybrids and that it isn't something we need to worry about. Now if they could just get Aisin to build reliable transmissions we would be good to go.

 

[32spoke]

I am more concerned about getting the turbo impeller speed reduced as much as possible. I am uncertain if the twin scroll turbocharger has a ball bearing setup or not. Regarding cooling…. Before folks have a nasty disagreement on this thread, please read this article by Garret, and how coolant can “siphon” through a turbo charger after the water pump has been shut off, if the cooling design has been engineered properly.
https://www.garrettmotion.com/racing-and-performance/choosing-a-turbocharger/water-cooling-for-your-turbo/#:~:text=Water%20cooling's%20main%20benefit%20actually,of%20the%20turbocharger%20after%20shutdown

 

[tacorancher]

I am more concerned about getting the turbo impeller speed reduced as much as possible. I am uncertain if the twin scroll turbocharger has a ball bearing setup or not. Regarding cooling…. Before folks have a nasty disagreement on this thread, please read this article by Garret, and how coolant can “siphon” through a turbo charger after the water pump has been shut off, if the cooling design has been engineered properly.
https://www.garrettmotion.com/racing-and-performance/choosing-a-turbocharger/water-cooling-for-your-turbo/#:~:text=Water%20cooling's%20main%20benefit%20actually,of%20the%20turbocharger%20after%20shutdown

Interesting - what is twin scroll? I saw that in my truck data sheet. Is it like a split turbo with two cylinders each supplying a turbine so you’ve got the power at half the RPM? Sort of like a twin turbo?

 

[32spoke]

Interesting - what is twin scroll? I saw that in my truck data sheet.

A turbo is basically an air pump, and based upon displacement of the engine, compression ratio of the engine, and air volume at maximum RPM are necessary to find the right turbo. But having a smaller turbo will provide better lower rpm performance, at the expense of degrading higher rpm performance, and the opposite is true.. large turbo for an application would require the engine to be higher into it’s RPM range before it is very useful and useless at lower rpm- turbo lag…

single scroll turbocharger is easier, cheaper to manufacture and install, and its overall size is more compact. It also produces better high rpm performance, and the downside would be poorer low rpm performance as well as a fairly narrow effective rpm range. On the contrary, a twin scroll turbocharger is more efficient due to less turbo lag, producing better low rpm performance, but the disadvantage is having a poorer high rpm performance and it is more complex in manufacturing as well as installation, so the overall cost is higher

 

[tacorancher]

A turbo is basically an air pump, and based upon displacement of the engine, compression ratio of the engine, and air volume at maximum RPM are necessary to find the right turbo. But having a smaller turbo will provide better lower rpm performance, at the expense of degrading higher rpm performance, and the opposite is true.. large turbo for an application would require the engine to be higher into it’s RPM range before it is very useful and useless at lower rpm- turbo lag…

single scroll turbocharger is easier, cheaper to manufacture and install, and its overall size is more compact. It also produces better high rpm performance, and the downside would be poorer low rpm performance as well as a fairly narrow effective rpm range. On the contrary, a twin scroll turbocharger is more efficient due to less turbo lag, producing better low rpm performance, but the disadvantage is having a poorer high rpm performance and it is more complex in manufacturing as well as installation, so the overall cost is higher

Cool thanks - I would imagine 2 cylinders are each powering a separate turbine in this setup but I’m not sure

 

[32spoke]

Cool thanks - I would imagine 2 cylinders are each powering a separate turbine in this setup but I’m not sure

This article does a far far better job of explaining it.
https://www.roadandtrack.com/car-cu...oll-turbo-work-lost-scrolls-of-turbocharging/

 

[tacorancher]

This article does a far far better job of explaining it.
https://www.roadandtrack.com/car-cu...oll-turbo-work-lost-scrolls-of-turbocharging/

That is so cool - great article

 

[TacoFreak]

Thanks for that link @32spoke. I had some idea of what a twin scroll turbo was but I understand it a whole lot better after reading that article.

 

[32spoke]

Thanks for that link @32spoke. I had some idea of what a twin scroll turbo was but I understand it a whole lot better after reading that article.

You are welcome!! They are expensive to replace when they fail, and they have more complexity due to their unique design

 

[tacorancher]

You are welcome!! They are expensive to replace when they fail, and they have more complexity due to their unique design

So I’ve been reading a ton about twin scroll and it’s very fascinating. It seems relatively simple in design as all you’re doing is splitting apart the exhaust channels of the four cylinders to get more even flow and avoid exhaust pulse canceling each other out. What I don’t know is if the scrolls feed into the same spot in the turbine or if the turbine has different spots where it receives each scroll exhaust (and perhaps different fan channels of some kind that work more efficiently at different rev speeds). That somehow changes the turbo power across the rev range. Either way twin scroll is excellent for low end torque and max turbo efficiency without the complexity, cost or weight of having 2 turbos.

 

[32spoke]

So I’ve been reading a ton about twin scroll and it’s very fascinating. It seems relatively simple in design as all you’re doing is splitting apart the exhaust channels of the four cylinders to get more even flow and avoid exhaust pulse canceling each other out. What I don’t know is if the scrolls feed into the same spot in the turbine or if the turbine has different spots where it receives each scroll exhaust (and perhaps different fan channels of some kind that work more efficiently at different rev speeds). That somehow changes the turbo power across the rev range. Either way twin scroll is excellent for low end torque and max turbo efficiency without the complexity, cost or weight of having 2 turbos.

On the exhaust port of the twin scroll turbocharger, it will have a split to isolate exhaust from the exhaust manifold, to port exhaust gas to one of two sets of exhaust impellers on the center housing rotating assembly/impellers. The second set of exhaust impellers and the porting of the incoming exhaust gas, make for an expensive turbo but more efficient. The exhaust manifold must be designed to work with a twin scroll turbo, to capture exhaust pulses… old school V8 cross plane crankshaft engines are big on using equal length primary tube headers to assist with exhaust scavenging…

 

[tacorancher]

On the exhaust port of the twin scroll turbocharger, it will have a split to isolate exhaust from the exhaust manifold, to port exhaust gas to one of two sets of exhaust impellers on the center housing rotating assembly/impellers. The second set of exhaust impellers and the porting of the incoming exhaust gas, make for an expensive turbo but more efficient. The exhaust manifold must be designed to work with a twin scroll turbo, to capture exhaust pulses… old school V8 cross plane crankshaft engines are big on using equal length primary tube headers to assist with exhaust scavenging…

So the split exhaust channels run to two different impellers attached to the same turbine? All the diagrams seem to show one impeller.

 

[32spoke]

This turbo design might be why the tuner dynos are showing a drop off of power as the engine rpm is in its higher range, when trying to extract more power. To me, it means that Toyota researched this design thoroughly, and gains can be made, but hard to achieve anything at the higher end of the rom range.

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