Featured As gas prices have dropped, so have owner's EV/hybrid loyalty

To provide counter torque it must generate

 

Actually it does both. At low speeds under 25 mph, generator. Above -25 mph it becomes a motor ... the so called heretical mode. Yet the torque sign remains the same. It took me a couple of years to finally understand it.

Bob Wilson

 

I think you are referring to the flexplate. It it a continuously applied clutch disk-like connection to the ICE that serves as a damper. It looks like a clutch, but is not. Its purpose is to smooth mismatches in speed between the motors (electric) and the engine (ICE). Whoever posted the video was mistaken. The Prius has no clutch.

 

But complex does not automatically mean higher maintenance costs.

 

Bob is talking about the mode where it acts as a motor and provides extra torque to the output shaft. This energy either is generated by mg2 or comes from the battery or a combination of both. Think of it as overdrive gearing, but in a continuously variable way (CVT + possible battery power).

I've got to say there is some conceptualy strangeness going on her. The Simplist car transmission is a manual, a small number of gears, a driver actuated gear shift and clutch plate. It also has lowest up front costs, but on average highest mainanance costs.

Now the hsd is mechanically simple, but is a much more complicated system. It has two big motors, inverters, big traction battery, lots of electronics to decide what the accelerator and brake pedal does to the motors, engine, and brakes which is a calculation, not a direct task. It is much heavier, more complicated, and expensive to install, and it needs a lot more space. It should have lower maintenance costs though as long as the expensive parts don't break after warranty.

 

The ongoing costs of a manual are highly dependent on the driver, though. A skilled driver can get them to have far, far lower costs than any ICE-only automatic, once you're looking at mileages over 200k or so.

But, the engines themselves are far more complicated and maintenance hungry nowadays, due to emissions standards and fuel economy standards. High pressure direct injection systems, sometimes dual fuel injection systems, turbochargers with complex control systems keeping the engine on the ragged edge of detonation, that kind of thing.

 

MG2 only generates electricity when braking/coasting. MG1 is the MG unit that can generate electricity while the ICE is running and send power directly to MG2 or to the battery (or both). Or generates counter-torque (using electricity from the traction battery) to create more torque for MG2/ICE to drive the wheels. And I wouldn't really say that the Hybrid power train has an output shaft like in a traditional transmission. It's more of chain coming off of MG2 that is connect to the front wheels.

As the HSD system has evolved, it has gotten cheaper and cheaper. The price differential between a regular RAV4 and the Hybrid RAV4 is only about $700 now. The up front costs have dropped by quite a bit now. Most of the expensive part of the HSD has been the battery, not so much the electric motors/transaxle.

MG1 is actually fairly small in comparison to MG2. You are correct that the system is more complicated at an electronic/software level, but after nearly 20 years of the system in use, Toyota has shown that their system is very robust and extremely reliable. More reliable than a lot of manual and automatic transmissions. Even a battery failure is not necessarily more expensive than a automatic transmission rebuild (this I know all too well from personal experience in both cases).

I don't know that I'd say that the space required for the HSD powertrain is all that much bigger than a gas-only version. Highlander, Camry, RAV4, and Avalon all have Hybrid versions and the engine compartment is the same size in the hybrid and non-hybrid versions. In some cases, a smaller engine is used, which helps save space.

 

Would this flexplate also give way if the ICE suddenly stopped for any reason and thus prevent damage to the eCVT ? That was stated to me and I would like to check the accuracy of that claim. Engine lock up rare nowadays, but happened in past when engine bits came apart and suddenly jammed the rotation. I was always happy when all the bits stayed in the engine compartment rather than popping up thru the hood or blasting downward.
As far as manual transmissions go, I say , "Bring back the crash boxes-->make these whippersnappers learn how to double-clutch if they want to drive the bloody car!!"

 

i believe we've had a couple piston rods through the crankcase iirc.

 

IIRC the same. Wasn't it a Gen II taxi that the drivers just let run dry of oil? But anywho we could that eCVT down and see if the "clutch" flexplate thingy broke loose or whether the evidence showed the whole eCVT came to an abrupt halt. In the latter case I would expect damage at least to the planetary gear system if not MG1 and MG 2 also.

 

funny thing is, if you have to replace on or the other, it's easier to replace both.

 

My son's 2005 Prius (Gen 2) had it's engine seize up a couple of years ago (he didn't keep an eye on the oil level), and the only damage to the Hybrid system was a failed battery pack (caused by running on battery power only and then repeated attempts to restart a seized engine. 2 of the modules were 1 volt less than the others, which caused a fault code, which means the pack is considered to be failed). I suspect that the Gen3 would react in a similar way.

 

This is not quite accurate. At speeds over ~25 mph, MG2 generates electricity that it sends to MG1 to provide counter-torque. In the Toyota paper, they called it 'energy recirculate' mode.

Bob Wilson

 

I'm trying to wrap my head around how it can generate electricity at the same time it's consuming electricity to propel the car down the road... All I can think is that it spends a fraction of a second generating electricity, and then another fraction consuming, and then back to generating, rinse and repeat...

 

Well, it really doesn't matter whether is generating MG2 or MG1. While one of them is acting as motor, the other one is acting as generator.

 

I would suspect that what it is, is that MG2 is NOT supplying power to propel the vehicle in energy recirculate mode, it'd be regenning, with MG1 supplying power that it gets from MG2?

 

In heretical mode MG2 is only generating electricity. The ICE is producing more than enough torque to move the car, so MG2 absorbs the extra torque and produces power used by MG1, which is rotating backwards to slow down the ICE. This is effectively overdrive, as the ICE is producing high torque at low RPM. The MG2->MG1 power flow avoids breaking the laws of conservation of energy.

When more torque is needed, less power is converted to electricity by MG2. Less power means MG1 slows its backward rotation and the ICE speeds up. At some point MG1 switches back to normal rotation and becomes a generator again, sending its power to MG2.

For a better explanation with interactive graphics, check out this page: Toyota Prius - Power Split Device

 

I wish that site had a way to show the torque flows and power outputs, though. (Speeds are far simpler to do, though.)

 

no question that ev/hybrid loyalty has dropped with gas prices, doesn't matter who is doing the generating.

 

The energy generated from MG2 goes to MG1 and back through the mechanical path. MG2 only goes into energy add mode when the power needed exceeds the engine power. Otherwise above 25 mph it only supplies power to MG1 for counter-torque to the engine.

It took years to finally understand it.

Bob Wilson