2022 Toyota Yaris - B mode

Dear Tom & Ray
In response to “What’s the “B” mode in a hybrid all about?” you’ve told Gayle that her husband has his head up his brake line, and then gone onto describe the regenerative braking system as increasing friction. This is clearly nonsense.

Are you able to describe how this system actually works, or do you not really know?

Is excess energy dumped to a resistor bank that requires extra cooling for example, or does it apply the brakes when the batteries are approaching their max state of charge?

That info was from 2009, many explanations available on the web.

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Can’t speak to the Yaris-B mode issue, but interestingly enough, one popular form of brake system design for trains (rail-road variety) works that way. The train wheels being braked turn a generator, and the electrical power generated from that either charges a bank of batteries (to be used later to propel the train ), or heats up a big resistor, which has its own specialized cooling system. Train brakes generate a lot of heat, and this method moves the heat problem away from the wheels. The backup brake system – in case the main brakes fail – on some trains are just blocks of wood, acting a brake shoes, rubbing against a part of the wheel. As you might expect, less than ideal. Said to be related to the deadly train wreck in San Bernardino, CA some years ago.

Where’d you get this? The resistors are used to prevent speed up on long downhills, not final braking. Next to no trains have batteries to charge up, very uncommon. And the brake blocks are not made out of wood, they’re cast iron or composite material.

From watching a tv show about this train wreck

I’m not a train brake expert of course. But from what I understand you are right the electric/resistor method (isn’t used for final braking, but to slow the train on long down-hills. Final braking is done presumably by the air brakes. That particular train did have the capability to recharge batteries from the electric-generating brake system, for later use as I recall, but part of that system wasn’t operational, which was part of the problem. The tv show indicated that the final emergency braking (which is done after all the other systems failed, using mechanical levers I think, not part of the air-brake or hydraulic brake system) used blocks of wood as the brake shoes, which of course was ineffective for that sort of problem.

The traction motors on the locomotive’s axles become generators during braking.

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Trains, being so heavy, must have an assortment of braking options:

  • Air pressure actuated drum brakes (similar in principle to how drum brakes work on cars), used as the main brakes for general braking needs. These will completely stop the train.
  • Electrical-generator type brakes (similar to how regenerative braking work on electric cars), used while the train is in motion, and not used for final braking. Some versions of this type simply heats up a resistor, the objective being to move the heat away from the wheels, and some versions charge batteries, the stored energy to be used on the next uphill
  • Emergency brakes, not sure how those work, but I’d guess they use a separate shoe from the main brakes
  • There may be a separate system for parking brakes too

I’m guessing some of these are used only on the engines, some only on the cars, some on both the engines and the cars. Anybody who knows about train brake system, please feel free to clarify. For example, is there a disc-type too?

Here’s lots of train brake info:
Brakes | The Railway Technical Website | PRC Rail Consulting Ltd (railway-technical.com)

Good info about train brakes in the above link, but from what I could see it doesn’t say whether or not there is a separate emergency brake system that uses separate shoes, independent from those used w/ the air brakes. Also doesn’t cover the version of dynamic brakes which charge batteries for later energy use.

Pretty sure that’s extremely rare.

I believe this is the utube version of the Mayday tv program about that incident. Emergency brakes applied at the 15:30 mark. NTSB analysis of the complete braking problem begins at appx 37:00. It ain’t pretty!

I drive a 2008 Yaris and if this car were to be any more basic, you’d have to start it with a crank. You do have to roll up the windows that way. Maybe luxury creep has gotten into the later Yaris models. Just like the Ford Thunderbird morphed into a bloated luxury car by the 1970’s.

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