Level of charge v. brake application

[xqqqme]

This is my evening for tech questions, I guess

When observing the level of regen created when I apply the brakes, I've noticed that the Charge gauge shows the highest level when I juuuuuuust *barely* tip into the brakes. Then, the Charge level starts to fall when either/both of two things happen...either when I maintain that very slight pressure and the car's speed has been sufficiently reduced OR if pedal pressure is increased beyond that very slight amount.

Why does the regen system seem to work best with such a slight drag on the brakes....and then go away?

[b1shmu63]

The brake has an on off switch that ramps up the current to the batteries in about one second to full regen when you lightly touch the pedal. As the car slows regen decreases. As the batteries charge regen decreases. As the engine RPM decreases regen stops completely at some point. If it did not, the brakes would be dangerously jerky at low speeds. Honda could have made regen variable, but it would have decreased efficiency, and added weight plus cost to the Insight.

[Dougie]

I believe that the pressure switch in the brake system is also involved. In my 2005, there is a clear difference in behavior if I lightly press the brakes (speeds under 20 mph) and if I press them enough to cause mechanical braking. I've read about how this works many times, and I'm starting to think that the behavior of the braking system was changed over the model years.

[Lee]

The brake-regen on the Insight only uses the brake light switch for an operator input. The IMA will determine how much regen you get, based on SOC, speed etc. This system is very simple and more complex systems exist. However this is the price you pay for having a first generation hybrid (yes it was the first on sale in the US, but the second mass produced hybrid in Japan). The amount of regen is relatively mild. This is to make sure that the braking force dose not upset the cars stability, because in some situations only the front wheels are braking. If the ABS system detects anything abnormal the regen is turned off and you have regular ABS brakes.

The HCH2 has a much more sophisticated system in that the brakes try to maximize the use of the regen before applying the front brakes. With moderate breaking the IMA regen and the rear brakes operate together. If there is any problem with the IMA, ABS or the control systems the brakes will operate as normal hydraulic brakes. It appears that you get the functional benefits of regeneration and the safety of the tried and tested hydraulic system. As I recall the HCH2 brakes are able to recover 3 times the energy as the Insight system (I assume this is under moderate to heavy braking). Don’t quote me on the numbers, it’s what I seam to remember from something I read.

[Dougie]

You're aware that unlike the earlier models, the 2005 model has a brake pressure sensor, I assume...

[Armin]

Keep in mind that the green bars on the "charge" gauge are very inaccurate. There is no simple x bars to y Amps equation. More bars don't necessarily mean more current and vice versa. It's really just a guess-gauge.

[Dougie]

It's pretty hard to figure out what's going on, but here is a specific example:

If I'm coasting down from 30 mph with clutch depressed and put on the brakes enough to activate the switch but not apply hydraulic pressure, the car goes into autostop at around 10 mph. If I wait until the car gets below 20 mph and then press harder on the brakes--enough to presumably activate the hydraulic switch--it will go into autostop even at speeds up to 20 mph. You have to press pretty hard--as if you want to slow down quickly.

[orac]

Dougie,
My 2000 MT behaves the same way. I think the computers are looking at the rate of deceleration to decide if you're really approaching a stop before it activates autostop.
___
Neil

[joecvt]

Dougie,

Are you referring to the sensor in the brake booster area that senses vacuum pressure? If so, all Insights have that sensor. It is used in autostop situations to insure that there is enough vacuum boost while applying the brakes with the engine off. If not enough vacuum, the engine will startup to increase the vacuum in the booster.

Or is there another sensor within the fluid brake lines that you are referring to and if so, is it used for the anti lock brake system.

JoeCVT -Just your average CVT owner

[Dougie]

According to the shop manual, there is a brake fluid pressure sensor that was added to the 2005 model. It's shown on page 19-21 of the manual, and appears to have two 3-contact electrical connectors and two brake lines. I can't find any reference to it in the IMA or other sections.

It appears to fit in the same location as the Creep Aid Solenoid Valve on the CVT model, shown on page 19-20 and on the overview drawing on 19-3.

I assume that there is one sensor for each of the brake hydraulic systems. Since they are three-wire connectors, I assume that they're pressure sensors, not just switches.