Forgot to shift out of B-mode before entering Freeway

If B mode is ICE compressor, how come you see the recharging meter increase as soon as you switch to B? This tells me that regenerative braking is doing more work here vs. ICE compressor.

 

As long as you have room in the battery, it does both. However, when the battery is full, the ICE revs will go way up and the Scangauge shows that there is no fuel injected (i.e. air compressor or jake brake mode)

 

As dogfriend says, it does both. The regeneration can respond faster, so you see that almost immediately. It takes longer to spin up the ICE with the valves configured for maximum drag.

 

you get more regen with foot braking.

 

Wow. The shading of Google topo maps is just amazing, isn't it ?

It doesn't take *that* much to fill up the battery and still have to brake. I use B mode on this decline sometimes, unless I want to give the rotors a little cleaning

 

We've got 25 posts and growing on this thread, and a good healthy debate about exactly when to use "B" and exactly what is happening when "B" is used. I'd use this thread as evidence, Toyota needs an instructional video explaining the what's and whys of "B" mode.

 

It's not a debate. The function and parameters of B mode are well known. We have been through this a dozen times before.

Tom

 

Again, the fact that we have been through this a dozen times before...is indicative that Toyota in manuals, guides and available information, isn't explaining "B" mode clearly enough for most people.

If the function and parameters of "B" mode were well known outside of this forum...and I'd argue even within, we wouldn't be going through this a dozen times before.

I'm not saying the correct information isn't in this forum, I'm not saying the correct information isn't within this thread. What I think would be nice would be a instructional video much like those created by Toyota explaining HSD and Smart Key. Because even if YOU know what "B" mode is all about, and how it's intended to be used, it's clear a lot of people don't, and a lot of new owners are in the shadows.

Then maybe we wouldn't have to go over this time and time again. Plus I disagree, it IS a debate...some are right, some are wrong, but just scroll through...you still have varying opinions as to when to use B mode and varying opinions as to exactly what is happening.

 

We go through this and other topics because people don't read. You can lead a horse to water...

Tom

 

Bit of calculation, using my basic mechanics equations:

The speed of the car at 70mph is 31.28 metres per second. Believe me, doing these calculations in metric is much easier!

Using the equation ½mv², and a mass of 1400 kg, kinetic energy at this speed is 685 kJ. If we were able to regenerate at a rate of 20 kW, which is about 100 A at the battery voltage of around 200 volts, it would take about 35 seconds to stop if no other forces were involved. The battery pack is fused at 120A, although the charge voltage is typically higher at up to 240V (the nominal voltage is pretty much for a fully discharged battery). There are also charging losses, so let's say 30 kW is the maximum that regen can achieve.

Air resistance accounts for about 14 kW - see the drag equation. Let's say that other losses account for 2 kW (I don't have a good model for rolling resistance). At these rates the car would slow by 2.4 mph in the first second, when travelling on the flat. It takes about 18 seconds to stop, in which time you've travelled 380 metres, or nearly one quarter of a mile. The (emergency) stopping distance quoted in the UK Highway Code is 75 metres at 70 mph, which I figure needs about 220 kW of stopping power on the flat.

However, if we're on a 1 in 6 decline, the car drops by 5 metres every second. The change in potential energy adds to the car's kinetic energy. Potential energy can be calculated using the equation mgh, where h is the height and g the force of gravity, 9.81 m/s². A drop of 5 metres adds 71 kJ of energy per second against the losses, for a net gain of 25 kJ per second, leading to an acceleration of 1.2 mph per second. It's obvious that we have to find some other way of scrubbing speed.

If you start with six bars of charge, it takes around 700 kJ of energy to fill the battery to the top of the eighth bar - call it 200 Wh, or four of the small car blobs on the five-minute bar graph. At a rate of 25 kW that's about 28 seconds. At 70 mph you've covered approximately 840 metres or about half a mile in that time.

I've almost certainly got some of these assumptions wrong - I think I've overestimated the drag as the cross-section area of the car isn't the maximum height off ground and isn't a rectangle, but that's a simple model. I'm also only recomputing the speeds and forces every second rather than using an integral, so the drag force will be excessive.

I've attached a spreadsheet you can play with: change the assumptions in column K, rows 1-8. I haven't allowed for less dense air at altitude or the temperature of the air. Numbers are roughly based on Gen 2 rather than Gen 3. If your assumptions give a negative deceleration in column G, that's an acceleration and the car won't stop. Otherwise K10 shows the time taken to stop and K13 the proportion of energy captured through regen, allowing for the charging efficiency.

 

Mike, I am not an engineer, so I am allowed to estimate ...
Figured *only* in metric -- I am way to lazy to use any other scheme:

g = 10
Filling up the battery from 4 to 8 bars takes about 0.3 kwh, or 1000 kw*s

Dropping 1 meter/sec is 14 kW to the drivetrain, so lets drop 1.8 meters/sec to fill the battery pipeline of 20 kW and have 5 kW left over to cover the resistances found at 15 meters/second on level ground.

So ... in ~ 50 seconds it's time to use B mode.