How does HICAS get YAW-RATE FEEDBACK in an R33????

[ACEMANN]

Is there ANYONE out there that knows HOW the HICAS system on an R33 receives "yaw-rate feedback". I have studied the R34's HICAS system diagrams (similar to the R33, can't find the steering service manual for the R33) and cannot find any inputs whatsoever that correspond with yaw-rates or any type of accelerometer inputs. I just don't see where the HICAS system is getting the yaw-rate feedback from, unless it is within the HICAS ECU itself.

Anyone know where this input comes from? Are there any R33 HICAS system diagrams out there?

Thanks for any help...

[predator]

lol - there is no yaw rate feedback.. It's not that advanced.

[GTRgeoff]

Precisely. It's simply based upon steering angle and wheel speed, which is why it is such a crap system.

Perhaps you are thinking of the GTR with about 3 accelerometers for the Atessa system.

[ACEMANN]

Precisely. It's simply based upon steering angle and wheel speed, which is why it is such a crap system.

Perhaps you are thinking of the GTR with about 3 accelerometers for the Atessa system.

Hmmm... interesting...then why did Nissan list this for the R34 in its press release in '98?

"The electric-powered Super HICAS four-wheel steering system with yaw rate feedback control is used to provide steering response faithful to the driver's expectations and excellent stability. This system newly incorporates a model-following control procedure like that used on the latest jet fighters, among other applications. Based on the vehicle speed and steering wheel input, this control procedure determines the target vehicle state and the rear-wheel steer angle needed to achieve that state is then determined. This procedure provides more accurate, fine-tuned control for enhanced tracking performance and improved convergence against external disturbances. "

Then I found this info on the R33, from J's Garage Export. Sounds like a copy-paste press release on their site:

"Yaw rate feedback control has been added to the phase reversal control procedure traditionally used in Nissan's Super HlCAS four-wheel steering system. With yaw rate feedback control, vehicle motion corresponding to the driver's intentions is first estimated from changes in the wheel speed and steering angle as detected by various sensors. At the same time, the vehicle's actual yaw motion is detected by a yaw rate sensor and fed back to the controller for comparison with preprogrammed target values. The controller then outputs a command signal to the actuator to adjust the rear-wheel steer angle. "

So what DID they change? Maybe they updated some of their vector-formulas in the ECU allowing the system to respond better than the first-gen system. Maybe it was some sort of software trick they used to "emulate" yaw-rate feedback. But they "say" for the R33 that motion is detected by a sensor and fed back to the controller. I am at a loss as to why TWO press releases mention yaw sensors for the HICAS, yet NO sensors seem to be used!

I am aware of the g-sensors for the ATTESA-ETS system...and given that I could not locate ANY inputs from such sensors into the HICAS ECU, I became doubtful of what I was reading, from even Nissan's press releases. Kinda strange. Any more input?

[ACEMANN]

Anyone out there have any more insight into this matter? If anything, could someone clarify what Nissan is advertising their system to do?

:headspin:

[Ant]

OK, I have a theory:

Thinking about what yaw rate really means - it is essentially the rate of rotation about the centre of the rear axle line. And this should be able to be derived from the angle of the front wheels (ie steering angle) and the vehicle speed - as per the description fron Nissan.

The only time I can think of where these inputs wouldn't reflect the actual yaw rate is in an oversteer or understeer situation, which would mean an accelerometer would be needed. But given that HICAS is supposed to stop oversteer/understeer, then maybe the assumption is made that these 2 inputs are all that is required.

Also obviously once the HICAS unit changes the rear wheel angle then this change would need to be integrated into the yaw rate calculation, however as the HICAS unit already has this info then this would be easy to do.

[ACEMANN]

OK, I have a theory:

Thinking about what yaw rate really means - it is essentially the rate of rotation about the centre of the rear axle line. And this should be able to be derived from the angle of the front wheels (ie steering angle) and the vehicle speed - as per the description fron Nissan.

The only time I can think of where these inputs wouldn't reflect the actual yaw rate is in an oversteer or understeer situation, which would mean an accelerometer would be needed. But given that HICAS is supposed to stop oversteer/understeer, then maybe the assumption is made that these 2 inputs are all that is required.

Also obviously once the HICAS unit changes the rear wheel angle then this change would need to be integrated into the yaw rate calculation, however as the HICAS unit already has this info then this would be easy to do.

Hey, that actually makes sense. Now that I think about it, when I compared the schematics of the hydraulic (older HICAS, no yaw-rate feedback) to the newer, electrical system on the R34, I noticed there were TWO rear-steering angle sensors on the HICAS actuator (NOT to be confused with the standard, steering angle sensor on the steering wheel). There are no such sensors on the hydraulic unit. They are the "rear-steering angle sensor" and the "rear-steering angle sub-sensor".

It might seem that they are necessary for motor control, but from what ant just posted, the additional input of the actual rear steering angle would be useful in additional calculations for the HICAS system. I guess I might be somewhat correct in assuming a "software trick" of sorts is used to perform "yaw-rate feedback".

I also noticed that engine speed is input into the newer HICAS ECU...something the older system lacks as well....

Also something to note: One reason HICAS "sux" for Z owners is because it sometimes induces understeer...something the yaw-rate feedback system would help correct...

Then again...what if the accelerometer is part of the HICAS ECU itself? It actually just hit me...if the yaw-rate is the angle of rotation around the center of the rear-axle line, then placing the HICAS ECU in the parcel shelf makes perfect sense. Z32's have the HICAS ECU right below the glovebox...and they use the older system. Even for the electric Z32's. There are just too many gaps in understanding this system and how it really works...anyone else have any insight?

[Ant]

Hey, that actually makes sense. Now that I think about it, when I compared the schematics of the hydraulic (older HICAS, no yaw-rate feedback) to the newer, electrical system on the R34, I noticed there were TWO rear-steering angle sensors on the HICAS actuator (NOT to be confused with the standard, steering angle sensor on the steering wheel). There are no such sensors on the hydraulic unit. They are the "rear-steering angle sensor" and the "rear-steering angle sub-sensor".

Might be 2 sensors as I thought the right and left wheels can move by different amounts (due to the suspension geometry)?

It might seem that they are necessary for motor control, but from what ant just posted, the additional input of the actual rear steering angle would be useful in additional calculations for the HICAS system. I guess I might be somewhat correct in assuming a "software trick" of sorts is used to perform "yaw-rate feedback".

They would be for motor control - so the control unit can move the wheels to the correct angle. And since the control unit has calculated what the angle should be, it then would feed that number back into the yaw rate calculation.

I also noticed that engine speed is input into the newer HICAS ECU...something the older system lacks as well....

I think on older cars the HICAS unit gets the speed from the ECU via the CONSULT data bus - on a Z32 you can query the HICAS unit from the CONSULT connector but I've yet to hear of someone being able to query the HICAS unit in a R33 or 34 Skyline - I've tried myself and the addressing scheme that works for the Z32 doesn't work. Which indicates that the R33/34 control unit has the speed as a discrete input rather than going to the trouble of tapping into the CONSULT bus.

Then again...what if the accelerometer is part of the HICAS ECU itself? It actually just hit me...if the yaw-rate is the angle of rotation around the center of the rear-axle line, then placing the HICAS ECU in the parcel shelf makes perfect sense. Z32's have the HICAS ECU right below the glovebox...and they use the older system.

That was my initial thought too - as you may know in R33 Skylines the HICAS control unit is located under the parcel shelf on the rear axle line. Though not dead centre, it is offset to the right. It may use a PCB mounted accelerometer, there are surface mount accelerometers available. Anyone know where the HICAS unit is in a R34?

On the topic of the effects of HICAS, does anyone have a critique of why HICAS is such a problem? I've read a lot of comments from people who don't like HICAS - usually drifters where it stops them from oversteering (which is kinda the point of the system!), but no real reasoned arguments as to why it is such a bad thing on a road car?

[ACEMANN]

They would be for motor control - so the control unit can move the wheels to the correct angle. And since the control unit has calculated what the angle should be, it then would feed that number back into the yaw rate calculation.

Seems we agree on that one...it appears to be the only logical explaination for their placement.

I think on older cars the HICAS unit gets the speed from the ECU via the CONSULT data bus - on a Z32 you can query the HICAS unit from the CONSULT connector but I've yet to hear of someone being able to query the HICAS unit in a R33 or 34 Skyline - I've tried myself and the addressing scheme that works for the Z32 doesn't work. Which indicates that the R33/34 control unit has the speed as a discrete input rather than going to the trouble of tapping into the CONSULT bus.

You are exactly right...according to the HICAS schematic for the R34, the VSS signal has a dedicated input to the HICAS unit. The Z32 system does indeed branch from the CONSULT bus

That was my initial thought too - as you may know in R33 Skylines the HICAS control unit is located under the parcel shelf on the rear axle line. Though not dead centre, it is offset to the right. It may use a PCB mounted accelerometer, there are surface mount accelerometers available. Anyone know where the HICAS unit is in a R34?

I was also a little apprehensive in assuming an accelerometer was located in the HICAS ECU for the same reason...it is over the axles on the parcel shelf (a near perfect location), but it was off-center. Not exactly optimal, but possibly still effective. As for the R34's HICAS control module placement...it is right over the axles on the parcel shelf...exact same location as the R33...very intriguing! I am going to see if UNISIA makes surface mount accelerometers...I believe they made the units used by the ATTESA-ETS system.

On the topic of the effects of HICAS, does anyone have a critique of why HICAS is such a problem? I've read a lot of comments from people who don't like HICAS - usually drifters where it stops them from oversteering (which is kinda the point of the system!), but no real reasoned arguments as to why it is such a bad thing on a road car?

Over here in the US, most Z32 owners don't like it because it "feels funny" or seems "vague" on the track. Plus, most of the cars over here have the hydraulic system, and very few ('94 and up) have the electric system. On top of all this, it is the older, SUPER HICAS w/out the yaw feedback. But I do agree with you, most people take it off to drift and what-not, and weight savings (the electric system is actually light for what it does).

HICAS has always seemed somewhat of an enigma as long as I have known about it, especially the newer systems. Most people trash talk the system without even knowing how it works, or even what could be done to make it better. It fascinated me to hear that the new Infiniti M45 here in the states has HICAS!

Ant...are you an engineer? I am very pleased to have found someone willing to dig deeper into the newer HICAS systems and how they work...I have purchased an R33 control unit, electric actuator, and loom and will be recieving them within the next few weeks. I'll probably crack the ECU open and find out what makes this system tick...

[ACEMANN]

Man I need to get back to work...:headspin:...but here is something I forgot to add:

The whole reason I realized SOMETHING was really different with the newer HICAS is when I watched a dyno video from Ex Vi Termini

Their R33 was on the dyno, running top gear at maybe mid-range rpm, when all of the sudden the rear wheels started to move. I thought to myself "I thought HICAS only worked when you were steering the front wheels..."

No one was steering the front wheels...it was the HICAS system detecting slight lateral acceleration and compensating for it on the dyno...really wicked to watch.

So, I realized that there was much more to the newer HICAS, and that "yaw-rate feedback" was much more than steering angle and vehicle speed...it was very much more an independent stability system.

I need to find that vid

[SIMANN]

Hey cameron...lol

I am ACEMANN's brother. Just saying hi :thankyou:

-Jonathan

[ACEMANN]

Seems like it would use a rate-gyro like this one to accomplish the task:

http://www.spp.co.jp/English/jigyou/jigyou-e.html

on the left side of the page, click on "motion sensors". When that page has loaded, them click on the "Silicon VSG Gyroscope"

In the device's description, it lists the following:

Applications

Automotive Yaw Rate Sensor

And this:

http://www.eetimes.com/article/showArticle...icleId=51200123

Electronic stability control employs accelerometers to measure a vehicle's lateral motion and gyroscope and/or silicon yaw-rate sensors to detect "fishtailing." The system's controller "listens" to the sensors, then individually actuates the vehicle's antilock brakes to bring it back under control.

Seems like it is well within reason to assume that a rate gyro is used within the HICAS ECU to detect the vehicle's yaw rate...not an accelerometer.

Back to work!

[Ant]

Yup, electronics engineer, how did you guess ?!

R34 HICAS unit has dedicated VSS signal input - interesting... Can you confirm whether or not there is a Consult bus input to the unit?

Silicon rate gyro - it is essentially a couple of accelerometers combined in one package to detect acceleration in the x, y and (if it is a 3d unit) z directions. They just call it the old-school 'gyro' name as this used to be implemented with dirty great big gyroscopes. Those sensors are also used in automotive nav applications, where dead reckoning takes over from GPS when no or intermittant signals are present.

When you get the R33 unit crack it open and take some pics, and we can work out what is what on the board....

Your comment on the wheels moving on the dyno reminded me of a review I read in a local mag here on the R34 GT-T - they commented that the HICAS had a self steering effect in crosswinds etc. So you could be right, the accelerometers are there to detect externally caused motion that can't be derived from wheel position.

Yep, have read the same comments about the HICAS making the car behave unusually on the track, though I guess those sorts of comments are coming from experienced drivers who know how to control the rear end of the car, whereas the HICAS takes over that function for those of us who aren't professional racing drivers!

And have also read the trash talk from others - they seem to have little or no idea what HICAS actually does for them. Blame the current fascination with drifting I guess, where your car is nothing if you can't do big powerslides! Personally I prefer to go round corners quickly, rather than sideways, but that's just me....

Also noticed that the M45/Fuga has HICAS, which surprised me as I thought Nissan had dropped the system. Not sure if the V35 Skyline/Infiniti G35/350Z have it - they all use the same chassis as the M45.

Better get back to work myself!

[ACEMANN]

You need to strike my last regarding the dedicated VSS input on the R34...it does indeed have a consult bus input tied with the VSS.

I have a link to the R34 HICAS steering manual...

http://www.andrew.ihostingonline.com/manua...shop_Manual.pdf

The HICAS chapter begins on page 122, with the control unit schematic on page 125. Page 124 lists the locations of system components.

I did a little more reading on the silicon rate gyros, and you are right. They are essentially just paired-up accelerometers. I am also aware of Piezo-electric units, but I do not know how accurate they would be for this app...they are used in R/C helicopters as a stability system and seem to work well.

So I guess we could say an accelerometer is used, however it is the "silicon rate gyro" that uses the accelerometers within its design to operate like a "real" gyro would. Very clever...

I really can't wait to see what the HICAS control unit has inside...it must be much more complex than the early systems. I was also pleased to hear about the article you read, describing a "self-steering" effect from the HICAS in crosswinds and the like...very-very intriguing. That basically confirms my thoughts after watching the dyno video. It seems Nissan engineers turned HICAS into a self-contained stability system that can act even without steering input. But when steering input IS fed into the system, it uses the yaw-rates from the gyro to determine if the car is in some type of over/understeer situation (the biggest problem that comes from older HICAS systems seems to be understeer in some turns)...what do you think? If this happens, then HICAS might relax the rear-steering angle OR increase it depending on what the rate-gyro sees. This might seem goofy, but this is they way I see it:

Old HICAS (no yaw-rate feedback)

You turn the steering wheel, HICAS says "ok, you're going X speed, and you turned the steering wheel X degrees, so I will deflect the rear-wheels X degrees in the X direction to help you through the turn"

HICAS completes the operation and does not monitor WHAT these inputs to the rear-steering angle are doing/have done to the car's yaw rate (inducing understeer or oversteer...big problem) The system DOES work, but there are times where the rear-steering angle might need to be tweaked midcourse to preserve the intial "target state" (as per the system description)...thoughts?

Newer HICAS (with yaw-rate feedback)

You turn the steering wheel, HICAS says "ok, you're going X speed, and you turned the steering wheel X degrees, so I will deflect the rear-wheels X degrees in the X direction to help you through the turn" then the system watches what happens via the rate-gyro, and might say "the yaw-rate is exceeding pre-programmed limits for this steering angle and speed, so I will adjust the rear angle to compensate and bring the gyro readings within acceptable limits"

That was really over-simplified I know, but it is how I see the new system working during cornering. When the steering wheel is more-or-less neutral, it seems HICAS focuses more on the rate-gyro, which is really amazing.

BTW, no "new" Nissan/Infiniti vehicles here in the states have HICAS except the new M45...I might see what they have to say about the system on Infiniti's website.

Phew! Last thing...I want to turn faster as well...I feel the trash-talk of HICAS is fueled by the desire to get the rear-end loose and powerslide everywhere (I am NOT including track driving/racing). I think HICAS is a very ingenious "street" system that could work wonders for the "backroads" driver, or those who desire more precise handling.

Once again I'm glad to meet you ant...hopefully we can unravel how the newer HICAS really works!

:headspin:

[ACEMANN]

Here's a good read on driver-assisted yaw control:

http://mr-roboto.me.uiuc.edu/IRS/PUBLICATI...NS/1999_ACC.PDF

Here's a few points worth noting:

The goal of yaw rate feedback is to utilize a measured variable to provide additional sideslip minimization at higher vehicle speeds

Drivers often describe the feel of the vehicle based on the dynamic model of the vehicle rather than time domain or frequency domain criteria. It is assumed that the driver has specified the desired performance characteristics in terms of a reference model <-------read this as the TARGET STATE as per Nissan's HICAS system description for the R33 & '34

The driver front steer input will act as a reference command to the MRC (model reference controller...you could substitute HICAS ECU here)of the rear steer model while simultaneously acting as a known output disturbance for the vehicle's yaw rate

So it seems very plausible that Nissan designed yaw-rate HICAS to utilize the "intended" control model of the vehicle (think of it as what you WANTED the car to do in the turn when you turned the wheel x degrees) from front-steer input via the driver to not only determine WHAT to do to the rear wheels, but to setup a "boundary" or a "guideline" for the HICAS ECU to follow by looking at a rate-gyro/accelerometer and determining if the sideslip is within the "initial" parameters specified by the drivers original intentions (the guideline).

A rate gyro/accelerometer MUST be onboard the HICAS ECU itself...the placement of the unit in the car, and absence of additional sensors put this within a 95% certainty for me. It also makes me realize that the sampling rate of the gyro and HICAS module would be important as well. Even the sensitivity of the gyro/accelerometer would be major variables in the system's performance. It makes me wonder if placing the HICAS ECU in a more central location above the rear axles (rather than off-center in the parcel shelf) would result in somewhat improved performance/response...

[ACEMANN]

bump

[Ant]

Owww, reading that makes my head hurt, haven't had to think about that kind of control systems stuff since Uni....... :headspin:

Yep, my conclusion on what they mean by 'model following' is more or less the same. Basically the system has a built in model of what the driver is expecting the car to do for a given steering angle and speed, and the controller dynamically adjusts the rear wheel angle to acheive that effect. And it isn't only about the direction the car is travelling in, the HICAS will also affect the balance of the car - it affects the suspension loading on each side as well.

I really need to figure out how to communicate with the HICAS controller - from what you say the R33/34 system is on the Consult bus (initially I didn't think it was), which means that it should be possible to establish communication with it via the Consult PC interface. If it is the same as the Z32 unit (for which the interface details have been posted online) then it should be possible to read out and log the various parameters including rear wheel angle etc.

Regarding the position of the controller - I would assume that the fact that it is mounted off centre is incorporated into the programming of the unit, therefore moving it to the centre would probably degrade rather than enhance the response, unless you were able to change the programming somehow.

Guess I'll wait to see your analysis of the internals of the unit!

[ACEMANN]

Owww, reading that makes my head hurt, haven't had to think about that kind of control systems stuff since Uni....... :headspin:  

Yep, my conclusion on what they mean by 'model following' is more or less the same. Basically the system has a built in model of what the driver is expecting the car to do for a given steering angle and speed, and the controller dynamically adjusts the rear wheel angle to acheive that effect. And it isn't only about the direction the car is travelling in, the HICAS will also affect the balance of the car - it affects the suspension loading on each side as well.

I really need to figure out how to communicate with the HICAS controller - from what you say the R33/34 system is on the Consult bus (initially I didn't think it was), which means that it should be possible to establish communication with it via the Consult PC interface. If it is the same as the Z32 unit (for which the interface details have been posted online) then it should be possible to read out and log the various parameters including rear wheel angle etc.

Regarding the position of the controller - I would assume that the fact that it is mounted off centre is incorporated into the programming of the unit, therefore moving it to the centre would probably degrade rather than enhance the response, unless you were able to change the programming somehow.

Guess I'll wait to see your analysis of the internals of the unit!

Were you able to take a look at the PDF of the R34's Super HICAS system diagram? It is a few posts above if you want a better view of how consult is interfaced with the HICAS control module.

I should be getting my HICAS module and loom soon enough (shipped from Australia today actually)...I will definately take pics of the internals and see if there are any obvious components worth noting. You are probably right about the location of the HICAS module as well...if Nissan had to mount the module off-center then they would have to take that into account in their calculations. Then again, how hard is it to mount the module in the center of the parcel shelf? Unless there is a great obstruction in the general area, I don't see why it would need to be mounted off to the side. Kinda strange IMO.

That article made my head hurt as well LOL, but it did provide some insight into some terminology and functionality that have been somewhat vague for me up to now.

Also, in reference to the "Model Following" function (Target State)... would any "fine tuning" of those values would lead to improved perfromance? I wonder how much interpolation of the pre-programmed values is necessary for the HICAS ecu to correctly determine the proper rear steering angle? If the data were incremented in smaller values the control module could more precisely determine the proper angle, given the actuator is up to the task.

I will definately post pics within the coming week or so...it should be interesting to see what is inside. From an intial inspection, it seems larger than the Z32 unit, so there must be much more going on inside. Should be interesting!.

BTW, I am also on a quest to locate the "Steering and Suspension" chapter from the R33's service manual...it contains all the schematics for the HICAS system. No such luck so far...

[ACEMANN]

For those that are interested, I just received my HICAS module and have seperated the HICAS wiring from the boot loom...I'll post pics of the HICAS modules PCB's in a day or two.

I have also traced the wiring, and it seems that the HICAS modules for the R33 and R34 are nearly identical. There are still a few wires I haven't identified yet.

[ACEMANN]

LOL...day or two...

As luck would have it I have been blessed with the COMPLETE R33 HICAS schematic...I have also completely seperated the HICAS wires from the boot loom. I have been able to draw a diagram of the HICAS control module pinouts, along with the wire colors AND their functions...this is 100% verified data and would be very useful for diagnosing those HICAS problems for the R33. I don't think this resource exists for the R33, so when I get done I'll have a nice doc to submit to the forum so that hopefully it can be incorporated into a tech doc somewhere.

I looked for a good month and finally stumbled across a guy that had the R33 manual in Japanese...he was kind enough to give me the Steering section that contained the HICAS system diagrams. I can't read japanese but I can read a schematic

I'll post pics of the HICAS module PCB's sometime soon...I would really like to contribute to the "Sky's the Limit" PDF that has all the tech data...the HICAS section is somewhat bleak, and doesn't (I think) even touch on the later Yaw-Rate Feedback system. Hopefully in a few months I will have a complete writeup. Of course, all of this is an offshoot from what I need to complete my secret project LOL...