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4WD Rear Wheel Torque Display
As far as I can figure, the X-Trail 4WD indicator lights on the console don't actually tell you much except which position the switch is in. And looking at the rear clutch, it seems that it is actuated by a variable electrical signal. This means it may be possible to monitor the signal with a voltage meter to see just how much 4WD is engaged at any time. My understanding is that the rear wet clutch arrangement will support variable engagement.
Has anyone looked at this signal? It might be an interesting mod to put a voltmeter or bar LED display on the dash to show how much 4WD is engaged at any time.
Greg Smith WA
Admin Edit: Thread title changed.
Last edited by jalalski, 1/Mar/2008, 10:43 am
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21/May/2006, 2:53 pm
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Re: Interesting idea for a mod
Speaking from my experiance from reading other ECUs, the dash light will be a simple microvoltage on/off switch coming from the ECU. I would seriously doubt if the voltage would change in a potential manner.
Think of it like a oil pressure switch which is simply a spring loaded switch that once reaches a certain pressure, the spring closes enough for contact.
For your scenio, you would need to isolate the pressure switch from the ECU and have a potentio (variable) sensor installed. Before you could do this however you would need to know if the sensor was going to affect other parts of the circuit.
Do-able, but very complicated without inside knowledge of the ECU.
Of cause you could scrap the ECU and run something like a Motec, this would solve a lot of problems. Darn expensive option tho.
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21/May/2006, 8:00 pm
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Re: Interesting idea for a mod
Hmmm. Not sure if I follow you. From what I can make out from the technical description in this forum's homepage, it seems to me the 4WD function operates like this:
The 4WD function is administered by the ABS electronics unit (makes sense because the ABS unit is connected to the wheel rotation sensors and "knows" the rotation speed of each wheel). When the 4WD drive mode is set in AUTO, the ABS unit looks for wheel slippage - the front wheels turning faster than the rear. When this happens, it applies a voltage to the magnetic circuit in the rear clutch that engages the wet clutch plates. It is possible that the voltage applied is variable - enabling the clutch to be partially engaged. Perhaps it starts with a small value and increases engagement (and thus torque transfer to the rear wheels) if the slippage continues.
When the mode is set to AUTO, the book says that the system will engage 4WD when needed. But there is no visual indication of the engagement. The dash lamp is always hard on (probably just connected to the switch).
If someone has a service manual diagram of the wiring to the rear clutch, I might be tempted to hook up a high impedeance multimeter to a few suspect wires to see if I can see the clutch engaging. This would mean you will be able to see if the system is applying 4WD at any time. Otherwise you never know what's actually going on.
Greg Smith
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22/May/2006, 12:46 am
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Re: Interesting idea for a mod
Hi Greg,
A couple of people have suggested this on the yahoogroup about a year ago.
The understanding is that the transfer of drive to the rear wheels is not simply ON or OFF, but is variable. I am sure I read somewhere that the drive can be up to 40 or 45% to the rear wheels.
One of the messages on the yahoogroup - there are more, but I think you may have to be a member of that group to view the messages.
--- Rich. X-013(c)
'04 S2 ST Auto. Nudge_roofracks_tow_tints_Lightforce_GME_BFG_TBS_home-made-bashplate_50mm-spacer-lift
Click here to see >300MB of photos and videos All For His Glory. |
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22/May/2006, 5:10 pm
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Re: Interesting idea for a mod
hi ppl the gtr skyline 4wd has a unit on the dash that tells you what drive is going to the front wheels or the back wheels
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22/May/2006, 7:11 pm
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Re: Interesting idea for a mod
quote:
hicksy wrote:
hi ppl the gtr skyline 4wd has a unit on the dash that tells you what drive is going to the front wheels or the back wheels
And given that the X-Trail 4WD system was based on the one developed for the Skyline ... you could be on to something here!
Quick, someone PM skylineguy (or whatever his username is), he might be able to help. Any idea what the display is like hicksy?
---
- Adam (MY04 Titanium Ti-L)
Full Hi-Tech exhaust,Koni shocks,Whiteline rear s/bar,front strut bar,K&N filter,eyelids,Pioneer DVD+iPod+Veh Dynamics+rear view camera
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22/May/2006, 9:45 pm
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Re: Interesting idea for a mod
If someone has an electrical wiring diagram showing the wires running to the rear clutch and where they come from, I might be willing to put a multimeter on them and see what happens in various modes. Anyone?
Greg Smith WA
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27/May/2006, 2:01 pm
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Re: Interesting idea for a mod
I have been directly emailing one of the yahoogroup members (uber_choppa) and he's given me permission to copy this email here to share and get feedback/suggestions...
Here's his email:
I have not made much progress since I first posted the issue. I have the components there to prototype a circuit...I just haven't got around to sitting down and tackling it. Have you got the vehicle manual / electrical schematic?
Background:
From what I can understand, pin 18 of the 4wd/ABS module switches the "4wd actuator" relay to ground. The N.O. contacts of the relay connect the 4wd solenoid valve to ground. So the relay essentially "arms" the 4wd system when it turns on. The N.C. contacts of the relay connect the 4wd warning lamp to ground via a diode. This means that if the relay is not on then the 4wd fault lamp will light - you can deduce from this then that the 4wd solenoid valve is always "armed" while the engine is running - otherwise the 4wd lamp would be on (so regardless of the position of the 2wd/auto/lock switch which is why it can be dangerous to assume the rear wheels wont turn just because 2wd mode is selected - better to pull the 4wd actuator relay
out and then you're safe!). The 4wd/ABS module can also turn the 4wd fault lamp on by grounding through its pin 16 - it would do this when it "flashes" from the overheat condition I guess. The diode is there between the fault lamp and the 4wd actuator relay so that the 4wd/abs controller can operate the fault lamp via pin 16 independantly of the relay.
The 4wd/ABS module controls the 4wd solenoid valve by varying current - not voltage to it. By varying current between 0-2.8amps it can control how much the electronic clutch (located in the rear final drive) grabs.
Proposed:
An ammeter in series with the 4wd solenoid valve should give a visual display of the amount of power being directed to the rear wheels. An existing LED ammeter kit could be used for a 10 LED visual display and be less intrusive to the signal to the 4wd solenoid valve - it measures the voltage drop (in millivolts) across the power cable of the 4wd solenoid valve. The signal is then multiplied and fed to an LM3914 dot/bar display driver IC and scaled so it reads full scale (10th LED) when it reaches
2.8amps (I guess).
The 4wd system could be manually engaged in an emergency condition (say, a system or sensor failure) by bypassing the 4wd/ABS contollers output to the 4wd solenoid valve. By applying a current of no more than 2.8amps, the electronic coupling could be turned on (you don't want to burn this thing out). A viable option is by adding a 2nd relay between pin 102 and the 4wd solenoid valve. When the relay is in its OFF state, it would allow power to flow through the N.C. contacts. When energised, the relay would disconnect the 4wd solenoid valve from pin 102. Another set of contacts (N.O.) in the relay would connect pin 102 to ground. The first set of N.O. contacts would then connect the 4wd solenoid valve to the alternative 2.8amp power supply.
These methods are by far the easiest, cheapest and more robust way of interfacing and modifying the 4wd electronic coupling signal.
I was under the impression that the all-mode 4wd system was based (albeit loosely - they carried over the smarts, not the parts) on the skyline system. For one, the skyline system could not be turned off and I believe it was rear wheel drive predominately. From what I've read, it used a hydraulic system to increase pressure on clutches in the centre diff to direct power to the front wheels. But the idea was there - g-sensor, wheel sensors, throttle position - all used to figure out how much power to send to the wheels.
--- Rich. X-013(c)
'04 S2 ST Auto. Nudge_roofracks_tow_tints_Lightforce_GME_BFG_TBS_home-made-bashplate_50mm-spacer-lift
Click here to see >300MB of photos and videos All For His Glory. |
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3/Jun/2006, 11:47 am
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Re: Interesting idea for a mod
quote:
basshead wrote:
I have been directly emailing one of the yahoogroup members (uber_choppa) and he's given me permission to copy this email here to share and get feedback/suggestions...
Choppa is a member of our forum since 2004, but he's not active. It would have been great to get Choppa come on board and talk about this mod in detail with the rest 
Last edited by jalalski, 3/Jun/2006, 5:27 pm
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3/Jun/2006, 1:29 pm
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Re: Interesting idea for a mod
He stated he's currently too busy to frequent our forums. I thought he was a member
--- Rich. X-013(c)
'04 S2 ST Auto. Nudge_roofracks_tow_tints_Lightforce_GME_BFG_TBS_home-made-bashplate_50mm-spacer-lift
Click here to see >300MB of photos and videos All For His Glory. |
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3/Jun/2006, 5:25 pm
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