Regen Braking and Tailgaters

When ever I'm switchin' over to B, I always keep an eye on my rear view mirror. If I can swing it, sometimes I switch o N and brake to bring the lights on if someone's behind me. It's a valid concern and it reminds me how differently I drive in my Prius as opposed to any other car.

 

Yes, that could be surprising to others and therefore dangerous.

Also note that you get poorer fuel economy in "B". When you're in "D" and take your foot off the accelerator the Prius does a goodly amount of regen braking all by itself. "B" should be used only when going down a long hill to avoid riding the brake.

 

Since I don't yet have a Prius, I'm only partially in the Prius mindset...

I've always planned to use the "B" mode in the same way I use the lower D2, D1 etc. gears on my automatic transmission -- when going downhill over an extended period of time -- braking via downshifting.

Otherwise, I'll use the brakes -- which will cause taillights to appear.

 

I have given this idea thought before. I would have to agee that it's potentialy dangerious. I watch cars by distance.. so to me, this is not a problem. A lot of people on the road watch breaklights. ( like my family ) some people freak out when i only start gradualy breaking when breaklights are in front of me. The differnce is.. i can tell what speed they are going. Most people have problems with that. A lot of times i'll just coast which will make me match their speed when i'm a car length away ( city streets ) This saves me fuel and keeps me from going nuts from switching between pedals. I wish everyone would pay attention to distance.. but people don't. They rely on lights.

The only time i use B gear.. i'm usualy still passing traffic. I get tail gaters all the time. It's natural if you're cruising. Everyone likes to fast. They burn fuel while i drive my Prius.

If someone is comming up on you quick.. swtich from B to D and flash your brake lights a few times quickly.. it lets them know you're a lot slower than them... then just switch back to B.. they will go around you or slow down fast.

 

Can't you just tap the brake pedal every once in a while, whether you are in D or B?

On a conventional car, tapping the brake pedal doesn't really do any braking, but does signal the tailgater by flashing the brake lights.

Is the brake pedal on the Prius more sensitive than that?

 

Everything on the prius is pretty sensative. The reason i say shift out of B is because the last thing you want to do is slow down even more. If you switch out, you'll gain a little speed and give the car behind you a little more time to realize you're going slower.

I use this methon on Highway 17 Betwen San Jose, CA and Santa Cruz, CA... it's windy road.. so warning time is very important. Some people do 60.. some do 80+

 

If you're not in B mode, and you don't have your foot on the brake, for clarification, the car uses the electric motor to slow you down ever so slightly. However, when using your brakes in any mode, it uses the electric motor as well, unless stopping hard (or under 8mph). Therefore, the only time B mode is really necessary is downhill long stretches, where if people are coming up too fast, they'll be off the side of the mountain in no time.

-m.

 

"B" mode lovers who do not drive in mountains, take this simple test: drive a couple tanks worth using "B". Note your MPGs. Then drive a couple more tanks without using "B" at all. Compare MPGs on all tanks.

 

Toyota, and all knowlegeable users, say never use B mode unless you are going downhill for a long distance.

However, I agree that it is a safety feature if the brake lights do not come on while in B mode. Although the lights do not come on in a conventional car that downshifts to slow down, very few peope do this except on a hill. Given how easy it is to abuse B mode as a braking method on flat terrain, I'd say Toyota made a mistake in not connecting B mode to the brake lights.

I have never put my car in B mode in all the 7 months I've had it. The longest, steepest hills I've ever been on required nothing more than taking my foot off the accelerator. That was along the southern edge of MN on my way to IA.

 

I don't see why shifting to B should be more dangerous than shifting to a lower gear in other cars.

I seldom use B, for the reasons others have given.

 

I use B mode every day and you have to scan the buss to see that your using no fuel when going down a hill in B mode to realize that it's not bad for fuel economy. Sitting at the stop light at the bottom of the hill with the ICE running because you left it in B mode does waste fuel. Normal regen down the hill in D mode is about +12 amps B mode about +18 amps. Same hill same speed different day. If you want brake lights along with B mode just lightly touch the brake pedal and I mean lightly, and you get about +19-20 amps regen with the brake lights on, no precipitable decrease in speed. This is in a 2k3 and I doubt the 2k4 will show much difference.

 

Evan I used my wife's 2k4 for almost 2 1/2 months off and on with my 2k3 and have noticed a slight difference in the braking application response. I will say there was a bigger difference between her 2k1 and the 4 and not nearly as much in the 2k3. I wonder if there were software differences that accounted for this. The 2k3 is very easy to get started in electric mode and the 2k1 was more difficult. The 2k1 also exhibited the sag when switching to S4 and the 2k3 never has. 60 amp regen is not seen very often but 57-59 amps is easily attainable. When Graham gets the Mark111 and people start using it they will get a really good picture of the complex nature of this car.

 

Ah! More geek stuff to come!! Good good good!!!

 

Evan - I believe you are correct about the regenerative brakes being different in the 04. I frequently go down a long hill, and if I use the brakes, the SOC always ends up displaying all green bars to the top of the screen. If I use "B," the bars do not rise above the blue section. What purpose, then, does the "B" mode serve? It apparently provides less regeneration, and if the friction brakes are not engaged when "B" is off, there is no danger of overheating.

 

the function of the B mode is if you get the battery to 80% state of charge you cannot regen any more and if you still need speed limiting B is the only method of achiving it. B mode provides extra drag on the car by forcing MG1 into reverse direction. It's still charging and the additional drag of the ICE helps maintain speed. I'm almost to the point now of cutting a brake line and putting a pressure switch in it and an indicator light to tell me when I actually have started to put pressue on the friction brake system.

 

B mode for extended periods is not recommended as it forces the transmission to run in a lower gear than is optimised. this results in the transmission possibly overheating.

although Toyota does not specify any parameters, they suggest using B mode for short periods of time only.

realize that light brake pedal pressure will be nearly all regen with very little (if any friction) braking so overheating would not be a problem. as i have been in the mountains a few times, this enough to slow one down in all but the most extreme cases ( i would assume. although i crossed over an 8500 ft pass in the North Cascades, B mode was not necessary and in no time did i feel the brakes were overheating or that i was anywhere near losing control over the speed of the car)

 

the tannny is in constant loading if you in D or B it doesn't make any difference if you over 42 MPH the ICE is turning and as such makes the psd turn in mesh. If your under the psd turns in mesh, there is no optomised speed for the psd. MG1 turns forwards or reverse up to 10,000 RPM MG2 turns up to about 4500 RPM and the ICE turns up to 5000 RPM and there is no way to optomally have it turn in any range of rpm. It's all computer contolled and the driver havs no real control. If the battery is at 80% state of charge friction brakes is all you have other than B mode. When the battery is at 80% B mode uses current from the battery to provide the load to slow the car.