i4wd Wizardry

There is a lot of misinformation going around about i4wd, mostly due to Honda doing a really BAD job of explaining what it does and how it works (save for the video below). Let's go over the basics.

Functions of i4wd module:

1. Soft locking the front axle

2. Electronic brakeforce distribution (EBD)

3. Hill start assist (HSA)

Here is an important detail: the front diff is NOT an open diff. It uses Cam/Follower type mechanical torque biasing. Although it is not common, some Subaru car models also use this type of diff. As long as both tires have some traction, it will lock itself without needing i4wd to use the brakes. It functions similar to a lunchbox/ratchet-style locker, but the engagement pressure is gained from the outside/axle side instead of the inside/ring gear side.

If there is some traction on both tires, torque biasing will keep them both rotating in sync. If there is a substantial loss of traction on one tire (on ice, in the air, etc), i4wd will engage the brake on that tire to re-sync them. When this happens, it is important to note 2 things: the amount of brakes required is about 1/4 of the input torque (this is why i4wd does not burn up the front brakes), and when the spinning tire is slowed it will slow the the exact same speed as the non-spinning tire (cam and followers lock).

EBD runs all the time and mainly looks at speed/tilt of the machine to determine how much brake pressure should be divided front and rear.

HSA is available in all drive modes including reverse. Activating it simply hold the brakes in place (only works if you are already stepping on the brakes) for a maximum of 5 seconds to allow you to take off without rolling backwards.

You can see the action of the cam and follower differential in this video. Note how the tires follow each others direction, rather than rotating opposite directions like an open differential. The second video is an explanation of i4wd from Honda, the video is about the Pioneer 1000, but its the same i4wd system used in the Talon.