I’m guessing the data comes from the ABS lead
I’d imagine its from the air lines knowing how much PSI to put into the air bags to keep them inflated at ride height.
Same as a fork lift measures weight by the amount of pressure/resistance of the hydraulic oil.
As with most weighing equipment I’d take it as a guide instead of gospel.
It’s a shame they can’t do the front axle, then you’d know your gross.
Micks answer makes sense here… I’m guessing its not on air on the steers?
It is done indeed through the ECAS by measuring the pressures on the airbags. Though if the tractor unit 4X2 has springs and not airbags then the front axle load is a calculation based on the axle load of the drive axle,wheel base and position of the 5th wheel.Soif you have a sliding fixed wheel and move it from the position it was in when calibrated then the axle load on the screen will be incorrect …Best way to calibrate the system as it can be done via dealer laptop or ECAS handet ,is to take the unit to a weighbridge weigh it and then calibrate so truck reads the same as the weighbridge ,the trailer has to be done separate ,the unit can’t calibrate the trailer …Rigids and muti axle units are different .I just used a basic 4X2 with springs on the front to keep it simple …I will imagine other manufacturers may have different ways to calibrate it etc ,but the basics of how the system calculates will be the same
Oh, I thought you could only weigh the front axle load if it was on air hence most 6x2’s can’t have it but if you specced air sus rather than springs on the front axle of a 4x2 it would work. I’ve only seen scania’s with this system, great idea.
I don’t know about scania.though DAF can calculate the front axle on springs ,but it can vary from model to model…some can’t calculate a load on the vehicle with front springs…An 8X4 will only give reading for the drive axles…And rigids again are different
Who drives a 3 axle tractor and single axle trailer?
And if the weight displayed is for a triaxle trailer bogey its about as much good as bugger all unless each axle bag has pressure sensors fitted and an independent feed.
As they all sit on a ring feed and each get the same pressure then you got 36 ton plus front axle load at least 6 ton and its still not lowerd the midlift.
Bking:
Who drives a 3 axle tractor and single axle trailer?
And if the weight displayed is for a triaxle trailer bogey its about as much good as bugger all unless each axle bag has pressure sensors fitted and an independent feed.As they all sit on a ring feed and each get the same pressure then you got 36 ton plus front axle load at least 6 ton and its still not lowerd the midlift.
It was a triaxle trailer, if it was single axle 8.9tonnes would probably make it overweight, the 8.9 tonnes is the combined weight of all 3 axles
I think the ECAS suggestion is correct, and the data is fed through the ABS lead. It levels the suspension to evenly distribute the weight I think.
Clever system, just a shame it didn’t have the front axle on, especially as scania front axles are rubbish and are easily overloaded when the other axles are well under (with midlift up)
Its fed through the brown/white and green/white CAN wires on the EBS/ABS lead.
For the trailer the info will come from the EBS modulator. The accuracy will probably be mostly down to how accurately, and often, it’s been calibrated. I could imagine the properties of the rubber in the airbags could alter over time affecting the result.
I would expect new generations of EBS will monitor the load on each trailer wheel if the information can then be used for stability functions etc.
Have found these to fairly accurate and can be checked on an axle weigh plate that are in most RDC’s we always drive the same unit so you can work out any discrepancies quite easily a definite godsend when using 4 x 2’s
Different trailers give different readings. Can be upto 4 tonnes difference. The trailer i’m pulling at the moment I load to 23 on the back and 13 on the unit (5&8). This is roughly 44 ton on the weighbridge. My usual trailer has a higher tare weight but I load it to 24 on the back!
They only work accurately on the level, with brakes off.