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: http://en.wikipedia.org/wiki/Yaw-rate_sensor
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!