[W126 Coupe] Universal dash symbols

[Steve Nervig]

Mister Magoo asked:


>

> Hello all,

>

> Here is a question that the whole world likely knows the answers to  

> except me.  I was asked earlier today....

>

> On a '95 E320 S/W there is a warning light above the odometer on  

> the face of the speedo, amber with triangle and (!) exclamation.

>

> On the rocker switch panel on the centre consol there is (I'm  

> quoting the owner now) "what appears to be a doughnut standing on  

> its edge with worms."  (Personally, I would say its an inner tube  

> with chains.)  Function-wise, it appears to turn its own tiny light  

> on and off.

>

> The lady doesn't have an owner's handbook and NEEDS one.

>

> Is it obvious that Benz-wise, I'm hopelessly stuck back in the  

> 123/124/126 1980's???

>

> - Bellamy


Bellamy, here is probably more than you would ever want to know about  
the ASR system. At the risk of incurring KBF's rath, here goes...

MB seems a bit confused on its name, and it's probably a matter of  
symantics and translation from the original German. Job 42-0800  
(w124) calls it Acceleration Skid Control, while the Owner's Manual  
calls it Acceleration Slip Control. Acceleration Slip Regulation fits  
the TLA. ASR stands for "Anti Schlupf Reglung" in German.

To understand the "snow chain switch", you need to understand ASR a  
bit. ASR is a control system that activates the brake on the spinning  
wheel and depending upon conditions, reduces engine power output  
until the slip stops. There are several stages in the ASR activation  
which occur in milliseconds and are transparent to the driver.

In the US, ASR was an option from '91-on, on non-4matic vehicles  
only. My 300CE has ASR, with the  /!\  in the speedometer, just like  
the 4matic. It's tied in with the ABS and has four wheel speed  
sensors and a connection to the acceleration control system. There  
are three different control ranges in the ASR control mode using both  
a drive moment control circuit and a brake moment control circuit.  
More info is also contained in Brake System job 42-0800.

The acceleration skid control (ASR) will engage at all vehicle  
speeds, if one or both drive wheels begin to lose traction and spin  
due to excessive acceleration. While engaged, the yellow function  
indicator /!\ in the speedo lights up.

With the ASR engaged, the brake is applied to the spinning drive  
wheel until it regains sufficient traction. If both drive wheels lose  
traction and spin, the brake is applied to both wheels and  
simultaneously, engine torque is limited.

As traction on the road surface increases, the allowable engine  
torque also increases again and the brake is no longer applied to the  
drive wheels.

As I mentioned, there is a brake moment control circuit and a drive  
moment control circuit. The three control ranges of the ASR are:

A. Control mode with one skidding drive wheel and at wheel speeds <  
40 km/h. The allowable slip threshold is higher for the Drive moment  
control than the Brake moment control, so the brake is applied to the  
slipping wheel. If it still slips too much, the Drive control comes  
in and retards the electronic accelerator control.

B: Control mode when both drive wheels skid or at a speed < 40km/h.  
Drive control has priority and retards accelerator. If wheels still  
skid, brake control is added.

C. Control mode when cornering at speeds between 20 km/h and 120 km/ 
h. Depending on lateral acceleration, Drive moment control comes in  
sooner than for mode "B".

The console mounted switch, the "snow chain" switch, when activated,  
increases the speed threshold of when each mode will start to engage.  
This "buffers" the ASR a bit and lets some slippage occur when first  
starting out from a stop.

There is no traditional locking differential; the asymmetrical  
braking independently applied to the rear wheels provides this  
function, sort of. MB has a different system for an automated rear  
end differential, called ASD "Autosperrdifferential".

Interestingly, I find a 1990 MB brochure mentioned that MB developed  
all three of their electronically controlled traction systems (ASD,  
ASR and 4Matic) in the same year - 1986.

The ASR was available in the S-class only (not in R107, W201 nor  
W124) in the Oct 88 GB "Recomended Price List for Cars and Factory  
Fitted Extras".

It cost ~1500 to 1700 in then-year British Pounds (including basic  
cost, tax and VAT).

Another brochure I have says that ASR was available in the V-8 models  
in 3rd quarter 1986.

ASR was available in Europe on the 1990 W124 six cylinder gas  
saloons, coupes and estates with automatic transmissions, but not the  
4 cylinder gas, or 5 or 6 cylinder diesel cars. It was offered on  
both the 1991 W126 and 124 models in the US. I believe it was  
approximately a US$2000 option. It came standard on the all 500E and  
E500 W124 from 1992 thru 1994.

Regards,
Steve


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