Monday, May 19, 2014

Tech Note: The R33 GT-R had ELECTRONIC SUPER HICAS + Yaw Rate Sensor!

So I've decided that, on occasion, I will do a "Tech Note" based on interesting stuff I find in those R33 service manuals I got recently.

So today, let's talk about SUPER HICAS. In the technical/service manuals for the R33, I found this page interesting (I've added English translation in BLUE):

HICAS is one area where there is lots of controversy. Some people swear it makes the car handle strangely and so you are better off without it. Others say it weighs too much - which might be an argument on the hydraulically driven R32 GT-R, but not only the electrically driven 33 and 34 GT-Rs.  (and yes, it's heavy on the 32... but if you remove it, you increase weight bias on the front wheels, which is not something you want to do... and is the reason why the battery was moved to the back in the 33, for better weight distribution. But I digress...)

Anyway, it appears that most people who lock out their HICAS, don't really understand how it works, at least in a technical sense. So, since I found this, I thought I'd share my findings. It won't change some people's minds, but for me, as a purist R33 fan, it confirmed that I want to keep it.

First, what is interesting is that the previous version HICAS, found in the BNR32,  did not have yaw rate feedback control, like the R33 GT-R did. There appears to be a lot of confusion out there with regards to this:

No doubt, these guys couldn't read Japanese nor did they have their hands on this manual I have. For those who can, see the above - the white is the "normal" SUPER HICAS (found in other 33s), while the grey is what was added for the GT-R.

The take away is that, compared to the "normal" SUPER HICAS, the R33 GT-R (manual doesn't say others) had the yaw rate feedback added, in addition to the inputs for vehicle speed and steering wheel angle.

Here are two photos showing the 33's yaw rate sensor - it's located in the trunk next to the battery:

Apparently there was a preset map of yaw rate values to correspond to the actual vehicle situation according to the driver's intent.  The system would read the actual yaw rate value, compare it against the pre-programmed values, and then cause adjustment to the rear wheel steering to match the driver's intent.

The next page of the manual describes the yaw rate sensor as a tuning fork, piezo-electric, oscillation gyroscopic type. There are basically two types that exist - piezoelectric and micro mechanical:

So I'm not sure if these kinds of piezo-electric sensor wear out, or need to be replaced. Would a purely digital one improve the performance of the HICAS? I'm also curious to know about the software and the pre-set map - how complicated is it?

The white part above could very easily handle having the rear wheels steer in the opposite direction at low speed in a linear fashion, and then in the same direction, at high speed, in a linear fashion.

The grey part - the yaw rate input must therefore be for unusual, high performance/race type situations where the car's rear end is purposely being slipped or where the traction of the road surface is slippery.  Naturally, this raises the following questions on how the MAP has been programmed - What happens when the car skids, or the rear end is sliding? And would there ever be a situation where something would cause the car to "wobble" at speed?  HICAS computer malfunction, for example?

Has anyone had any experience in reading the HICAS Map?

Finally, I wonder what, if any, improvements were made to the BNR34 Super HICAS ECU and its programming. Obviously the 34 has a slightly shorter wheelbase, which means that the rear wheels would need to steer at slightly less of an angle to give the same level of response as the 33. This would suggest that transplanting the 34 HICAS ECU into a 33, would not have a beneficial effect, unless there was something else improved about the 34 ECU, such as better maps, or faster processing, etc.  So I will have to research this...stay tuned!


Stj88 said...

I wonder what system Nissan uses on their new cars (V36 Skyline, Fuga Y51) Because they don't call it HICAS anymore but 4WAS.

マット said...

Interesting bit of info! Can't wait to read more about it.

Ibo said...

Very interesting write up Aki. As always.

But I for my part will get rid of mine.
While it certainly adds and is part of the essence of the GTR, story like these:
creep me out.

Aki said...

Stj88, good question. I've heard the new 4WS steering system on the Fuga Y50 wasn't well received, however the Y51 version is much improved.

I searched online for Japanese articles on locking out HICAS, and most seem to focus on the 32. One article I found warned that if you buy a used car (a 32?) with a lockout bar, then better check the power steering pump for premature wear. OR at least be on notice.

Ibo, good to hear from you! Well I can understand your worry - for sure if you lock it out then it's one less thing to go wrong. I did read the link, I am relieved to see the poor guy is ok, but he did mention that he did not reset the HICAS properly after he disconnected the battery, and he did try to power out of the rear end slide. Until I replaced my G-sensor with a digital one, I never had any luck powering out of a slide, instead I spun like he did (on a race track). Now, I can actually trigger the front wheels to pull me out of a slide (I did this at low speed in the rain). In any case, I'm not saying the guy did anything wrong, in fact he did not place the blame 100% on HICAS like most people do.

The other thing which is a mystery for me is, I hear about all these accidents that are blamed on HICAS from overseas, but never in Japan. I wonder if that is due to stricter Japanese maintenance procedures (i.e. most people take their cars to dealers, who are expensive and love to replace with NEW parts...)

In any case, the bottom line is, these cars are getting older, and things start to break when they do. Part of my modernization motivation is to get the car performing when it was fresh from the factory, if not better and to keep it that way long term.

Ibo said...

Thanks Aki, had the worst case scenario with importing a GTR. But it's back on rails now ;)

Most of the Hicas hicups I heard, involved some thinkering with the car before hand.

Your's already is better than factory :thumbup:

Karl said...

As mine never had a Yaw Rate Sensor I'm still happy I ditched it! In fact I never gave much thought to the HICAS system until the warning light started to randomly come on and then after removing the system I personally found that the car felt so much better (notice I say felt and not handles).

Rob McAllister said...
This comment has been removed by the author.
Rob McA said...

I had some interesting experiences with my Yaw Rate Sensor. Mine Gtr is a 96 VSpec. I noticed when the car was cold and I braked hard, the rear would step out to the right quite noticeably. As soon as you lifted off the brake the car would straighten up.
I carried out a HICAS test, all seemed OK.
I purchased a second hand yaw sensor and fitted it to the car. Amazing difference - the car didn't step to the right under hard braking and wandering on the road that I had put down to road camber had noticeably reduced.
I set about comparing the 2 yaw sensors. I built a test gig that applied 12 volts to the yaw senor and then measured the output voltage of the yaw sensor. At zero movement the good sensor read 2.5v, if you moved the sensor to the left the voltage would increase, and if you moved the sensor to the right the voltage would reduce (or maybe the other way round - I have forgotten). When you stopped moving the yaw sensor the voltage would return to 2.5 volts.
When I powered my old sensor up on the test gig, it immediately showed about 0.5 volts and slowly over about 10 minutes increased to about 2.0 volts. testing the same way saw similar but smaller movements in voltage as compared to the new sensor. With a bit of testing using instant freeze, I located an electrolytic capacitor that perhaps had gone dry and wasn't working. I replace the capacitor and the original yaw sensor is working like the new one.

Aki said...

Hi Rob,

WOW! That is awesome, you know I've asked around here in Japan and people all say "don't worry that bit doesn't break." Interesting to see that you proved them wrong.

Maybe this is a part I need to stock up on?

Anyway thank you for the extremely interesting comment!