Can Anyone Explain How And When To Use The B On The Shift Lever?

[Joseph D]

I live in a very hilly area and use "B" every time I descend a hill. However, no one has been able to tell me exactly how it works.

There are 3 ways of braking with a toyota hybrid. Regenerative braking where a generator charges up the HV Battery, engine braking where the petrol engine is spun like an air compressor, and good old friction brakes. Nornally, regenerative braking is used but when the HV Battery is full or will not provide enough braking power, the other methods are called up (this is done automatically). Putting the car in B mode switches engine braking on permanently. It is usefull on long steep descents where you don't want the car to 'run away'.

So, therefore, as engine braking is introduced in "B", more energy is wasted as heat through the engine and less amount of energy is captured and stored in the HV Battery, due also to a lower a level of regenerative braking. Therefore, unless you have a long downhill (and by long, I mean 5-10 minutes or more continuous downhill) it is better to, contrary to the old wisdom, increase regenerative braking by riding the brake pedal to hold your speed. As long as it is a gentle amount the friction brakes will not be engaged, so you should not encounter brake fade, or risk setting your brakes on fire, the reasons why we would not ride the brakes in a conventional car.

Once the battery is full, the management computers will bring in the engine braking in any case. This is an exciting event when it happens to you the first time. LOL.

Also, if you have descended a decline in "B" and your HV battery isn't full when you have reached the bottom, then in actual fact you need not have used "B" in the first place.

HTH.

[IanIanIanIan]

I have been told that the 'B' engages an electric retarder so the engine does not spin nor is there any regeneration.

In the UK most coaches and higher-end lorries have retarders to prevent over-speeding down long hills.

Without 'B' the Prius would only have its brakes to do the same job as it can't change down a gear.

http://en.wikipedia.org/wiki/Retarder_%28mechanical_engineering%29

[timberwolf]

This is a better link as it actually describes what the Prius does!

http://techno-fandom.org/~hobbit/cars/b-mode.html

[r04drunner1]

We have some steep downhill 30mph zones around us and it works well for me on these, keeping me at the limit

I find it's much better to use Cruise Control to keep to the speed limit on steep downhill roads. CC gives you more regeneration than B mode does. Also CC does not waste energy spinning up the engine. In CC, if the car is still going too fast, you can always press down on the CC control. That increases regeneration and slows the car down.

[Joseph D]

I have been told that the 'B' engages an electric retarder so the engine does not spin nor is there any regeneration.

In the UK most coaches and higher-end lorries have retarders to prevent over-speeding down long hills.

Without 'B' the Prius would only have its brakes to do the same job as it can't change down a gear.

http://en.wikipedia.org/wiki/Retarder_%28mechanical_engineering%29

You have been mis-informed. This first sentence is without a doubt totally incorrect.

The link in Timberwolf's post (for which I was also hunting) does, as he says, describe what the Prius (HSD) does.

This is a better link as it actually describes what the Prius does!

http://techno-fandom.org/~hobbit/cars/b-mode.html

[twohats]

Anyhoo,

to answer HelenT's question in post 10, if you accidentally push P or go to R while moving the car will go into neutral.

Just push the lever to D again and away you go. Simples!

[HelenT]

Anyhoo,

to answer HelenT's question in post 10, if you accidentally push P or go to R while moving the car will go into neutral.

Just push the lever to D again and away you go. Simples!

Thanks for the simple answer twohats :-) That's all I needed to know.

[johalareewi]

if you accidentally push P or go to R while moving the car will go into neutral.

More precisely, if you are not moving slowly.

If you are doing 1 or 2 mph, it will actually go into P or R.

Not dangerous to the car otherwise you wouldn't be able to do it, but a bit of a shock for you.

P for Panic is handy to remember in case your Prius becomes a runaway ;) (or your car mat jams the accelerator full on). Just hit the P button and the car will go into N mode and you can glide to a halt.

[Cyker]

Uh, that doesn't sound like a good idea at all!

[timberwolf]

Yikes, I wouldn't want to engage the Parking Pawl at 1 or 2 mph on my car.