Plugin transmission

Check out John's Stuff - Toyota Prius and more Lots to read should answer most of your questions.

 

"B" is not really for braking assist.

The only time you might need it is on a extremely long downhill grade. It reduces regen braking, brings up engine rpm and shifts braking to "engine braking". The objective of using "B" is to forestall charging the battery to the point that the car stops regen braking and switches back to friction brakes.

I've used B mode a few times, coming down a ski mountain, and even then I'm not sure it was warranted. It raises RPM so much I'll chicken out, slip back into D.

 

The lack of gears & shifting prevents it from being called a "transmission" as most people know them.

There are power carriers permanently connected which transfer energy in a variety of ways. It connects the gas engine and two electric motors to the wheels. They rotate at different speeds & directions to optimize efficiency.

The plug-in model takes advantage of that by powering the traction motor more than with the regular model.

 

Does anyone know how the plugin transmission works?
Toyota Prius - Power Split Device

Is it electronic. What speed can you safely use "B" braking?
Yes, it is software controlled and uses two electric motors.
You can safely use B at any speed, you should only be using it when descending long downhills.


Any problems with accidentally hitting the shift knob when driving?

Is the computer smart enough not to shift if accidentally hit ?

You can't accidentally shift to P or R above about 5 MPH, you will go to to N.

 

So in a PiP...B mode would be even more dubious, correct?

 

Almost. B mode in HV mode (AKA all the time in a regular Prius) does what you say. B mode in EV mode in the PiP only *will* actually increase regen braking to slow you down more.

 

Using "B" to prevent exceeding the usual "full" capacity of 85% is handy... in a regular Prius. In the plug-in model, you've got quite a bit more actual kWh space available. So, taking advantage of that with regen makes sense.

 

I use B gear in EV mode all the time. I use it to slow down before cornering and there is no need to worry about ICE starting -- like in the regular Prius. PiP battery can handle B at all EV speed.

To summarize, at and below 62 mph, B is all electric (all regen into battery). Above 62 mph, it'll be both electric and compression braking using the engine.

 

If you don't trust it you can swap out the little shift knob for one with just a ring of push buttons mounted on the console. No knob sticking up.

 

The worst that can happen by hitting the shift knob is going into Neutral. The computer isn't going to let anything destructive happen.

 

it's an easy diy, there is at least one thread on it. they run about 200 bucks.

 

The car's programming automatically takes into account a LOT of the presumption of manual tactics involved in this subject! In a PiP the "B" mode is truly dubious because while it will provide regenerative braking on long downgrades with less opportunity of topping out the traction battery while reducing wear on the mechanical brakes, there is far more battery capacity to "fill" so less reason to use the "B" mode unless regenerative braking isn't sufficient to control the downhill speed of the car. During highway driving, it is imminently sensible to use cruise control to maintain speed in order to maximize fuel economy, and in fact when the traction battery reaches its charge limit (unlikely in a PiP unless you've just crossed the continental divide in Colorado), the computer will automatically make use of engine braking (automatic "B" mode) and taper off use of regen braking. This often surprises the driver who doesn't have a good grasp of how these cars operate, since the engine suddenly ramps up really quickly and the sound is completely counter-intuitive for a downhill run! The computer limits ICE rpms to under 4500 in any case, so while the sound falls into the "what-the-heck-is-this" category, the real implication is fairly tame compared with the way many stick-shift drivers rev up their 4-cylinder engines on city streets. But from a practical viewpoint, using "B" in situations other than when rationally necessary is not well-advised, because it is revving the ICE which translates to wear, however slight. And as to the "transmission": enough can't be said to dissuade the use of that word with respect to Hybrid-Synergy Drive. Certainly in terms of what we all know and hate as a "transmission", this box is definitely not one of those! No traditional friction components (wet or dry) to wear out or produce particulates, no gear changes at all, no nothing like a "transmission"! The traditional thousands-of-moving-parts transmission is completely out of the picture with the Hybrid-Synergy Drive system. The grossly overused word "revolutionary" is uniquely appropriate for this brilliantly clean and simple implementation!

 

I think the general understanding of what B mode does in the PiP is that it first makes regeneration more aggressive than the simple "idling" mode of just letting off the throttle pedal; that is , B is the equivalent to lightly pressing the brake pedal. Only if the battery is full will it employ engine compression braking, with no fuel, to dissipate energy. In the standard Prius, the battery is so small that the system very quickly has to revert to engine compression, but with the PiP, there is a lot more battery to store the energy in. I'm not sure but I think this depends on whether you are in EV or HV mode in the PiP; the "experts" here can clarify this.

The main reason for B mode seems to be a legal mandate that requires that automatic transmissions have a way to "downshift" to use engine braking to avoid "fade" on friction brakes on long downhills.

 

PiP will not start the ICE below 62mph. All the braking in B is done by the battery (recharging).

This is not true with the regular Prius where compression braking will start above 25mph.

 

In the simplest terms, the way I understand it, is to imagine a conventional automotive rear differential with a gasoline engine attached to one rear axle, and an electric motor attached to the other rear axle. The power is delivered through the drive shaft to wherever you want in this example.

The two motors work together (like the hybrid synergy-drive) but the faster the electric motor turns, the slower the gasoline motor turns (and vice-versa). So in effect the speed of the electric motor controls the gear-ratio of the transmission, and therefore the gasoline engine RPM, even though there's no "transmission" per say.

Since a gasoline engine performs best at certain speeds, the electric motor is used to control the gas engine; running at certain speeds for certain tasks. The result is that the gas engine doesn't rev like in a conventional car, it tends to run at certain fixed speeds most of the time. This is accomplished by computer control. Although it seems to work like a CVT, it is even simpler than that. The differential power-sharing is accomplished through the planetary linkages in the Prius transaxle.

 

I tend to never worry any more about shifting at the wrong time. Newer transmissions are fool-proof. With my previous car, the Corolla, I made a habit of throwing it in low gear as soon as I wanted to decelerate, regardless of speed. The computer ensures that it down-shifts at the right times, and I only need to add a touch of braking now and then. I learned this after many years of owning and driving vehicles, and I never had transmission problems with any of them. In fact, I've had brake pads lasting well over 150,000 kms.

With my new Prius however, downshifting has little value in everyday driving; I've had to re-learn using the brakes to regenerate electricity. On the steeper hills, I have used the engine braking option, when the hybrid battery no longer takes a charge, and I want to save the brake pads.

 

but up to a point ... aren't even the brakes strictly all regen? ... maybe depressed somewhere between ¼ & ½?

 

Yes, HSI bar shows when it would end the pure regen.

When I shift into B in EV mode, the CHG region in the HSI goes full then drops to about 1/4. I can increase the CHG bar with depress of the brake.