# How does HICAS work?



## Fallout (Feb 13, 2007)

Ok, so I know the basic principle of our HICAS. When it all goes wrong, the rear wheels steer a bit and save you from hitting that tree. I've found out it steers about 1 degree max and is speed dependent. But what I can't seem to find info on is exactly what they do, and when? By that I mean, if you swerve right, and the rear of the car starts to step out, in which way do the rear wheels actually steer, and by how much? In what situations do they actually move and in what way to help you recover?

I know it's not something I need to know, but I love Skyline gadgetry and want to understand it more. Anyone know the actual technicals of when and how far and in which direction it moves?


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## Mookistar (Feb 5, 2004)

there is a very good technical diagram on the forum.... somewhere

hopefully somoene will find it


mook


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## Fallout (Feb 13, 2007)

Yeah, that'd be awesome if someone can dig that out. I've been looking through countless Hicas threads on here, but they're mostly about "To hicas or not to hicas" etc. Well, I'm firmly in the "to hicas" field, because I love gadgetry and think it's part of what makes the car what it is. 

I found a bit more info for it online which makes things a bit clearer though, at AutoZine.org ...



> However, Nissan Skyline GT-R still proved that 4WS is worthy for demanding driving. Aided by computer, its Super HICAS system enable tightly-controlled power slide that cannot be implemented by any alternatives. When attacking a corner, the rear wheels will steer in reverse first in order to sharpen the initial steering response. Then, when sensors sense that the car responds to steering, the rear wheels will steer in the same direction as the front wheels, thus immediately introduces rear-tyre slip which help adjusting the attacking angle. Since the computer is monitoring the whole process, the amount of oversteering is always under check. You need not to be afraid of losing control.


Not exactly detailed info, but if it's accurate, it's very interesting. I wasn't aware HICAS turned both in and out in the same cornering move to promote a more responsive turn. Cool stuff. Gives me more info to annoy everyone with when I ramble on about my car.


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## Ian C (Jun 3, 2003)

I have a proper nissan technical document at home.
not read it yet, but i'll have a look through and scan the bits that answer your questions.....
Ian


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## Fallout (Feb 13, 2007)

Thanks mate. That'd be quality. :thumbsup:


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## Ian C (Jun 3, 2003)

Just pulled the document out....it's 29 pages!
I'll PDF it tomorrow morning, but no idea how to host it........anyone?
Ian


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## Fallout (Feb 13, 2007)

I can host it if you email it to me. Will PM you with my address.


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## Demon Dave (Sep 15, 2002)

simple diagram on how HICAS works at various road speeds:


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## skyline69_uk (Jan 6, 2005)

Demon Dave said:


> simple diagram on how HICAS works at various road speeds:


It uses the speed from the VSS (Vehicle Speed Sensor) which is why messing with this signal by adding in a kph/mph converter messes up the HICAS.


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## Ian C (Jun 3, 2003)

All done.....

code
ed3a2e58d114aa8a9e2c45d72a4cc2a5

Link
HostMyFile.co.uk - The Free File Host

Ian


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## ru' (Feb 18, 2007)

Great doc - cheers!


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## Ian C (Jun 3, 2003)

Can we move this thread to the technical area????


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## Hugh Keir (Jul 25, 2001)

Same diagram as above with a bit of text


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## Mookistar (Feb 5, 2004)

thats the diagram i was waiting for, well done Hugh


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## Fallout (Feb 13, 2007)

Nice diagrams guys. Also Ian C, cheers, I'll check out that download when I get home (at work now!). 

Btw, I've read a few of those threads about converting your speedo messes with the HICAS, but they always seem to be talking about R32s. Is the problem the same with the 33 and 34?? My car (33 GTR) was converted to MPH, although for the most part it appears to drive fine.


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## dave100 (Oct 23, 2006)

I am interested in this reply as mine has been converted to mph and seems to drive ok but as its my first skyline i have no reference to judge it by.


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## Fallout (Feb 13, 2007)

Dave100, is yours a 33 too?


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## dave100 (Oct 23, 2006)

Yes mate it is but i was told that the conversion messed with the attesa but it seems to work ok too  seems a shame to have to reconvert to kph again!


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## Fallout (Feb 13, 2007)

I've heard about the atessa getting messed up by it too, but I'm not sure how? I don't know exactly how the attessa works, but at a guess I'd say it's torque related? Or perhaps when it senses a speed difference in the front and rear wheels? Mine isn't V-Spec, so I dont have the left/right torque split I believe you get with V-Spec, but my attessa seems to do the job. Gauge goes up when I accelerate hard, no wheel spin unless I hammer it to death.

This is definitely something I'd like to know more about. If my atessa and hicas aren't working properly just because of my speed conversion chip, then I want to put it right so I get the right performance out of the car. Having said that, I haven't really noticed any problems with hicas or attessa. 

Edit: Mine is the only Skyline I've ever driven too, so I have no reference either.


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## MartinC (Jan 1, 2006)

Hicas is not operating properly as you have a speedo conversion chip, you might not have noticed it but the speed dependant bit is not calibrated right, as your ecu is not seeing the correct speed.

rip out the convertor and get a 200mph face made for your speedo.


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## 323ian (Jun 26, 2006)

I cant see how attessa is affected by the speed is it?
It runs off a G force sensor and speed signals relating to the front and rear wheels, not road speed.

I am afraid i binned my hicas as wanted to drive my car, not have it drive me!

Fallout, the vspec has the same attessa as a non v spec.


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## cokey (Sep 11, 2003)

I have an animation of its operation in japanese, worth a look.
2_attessa.mpg
If it doesnt work ?
Nope I cant post attachments.
I will E-mail it to someone that cares.
Pm me
c


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