ADS hydraulics

ADS is short for Adaptive Damping System (german Adaptiv Dämpfung System). It is hydraulic operated and electronically controlled system. It covers two functions. Constant vehicle level regardless of load and variable electronic control of suspension damping.

System consists from following main components.

Dampers

Dampers are shock absorbers that are divided into 3 components.

1. Strut (5)- by function it is hydraulic cylinder. When tire hits bump cylinder rod is pushed in cylinder barrel and oil is pushed out of strut. When tire falls in pothole cylinder rod is pulled out of cylinder barrel and oil is sucked to strut. Additionally by filling the cylinder with pressurized oil cylinder extracts. This is then leveling vehicle up.

2. Damper valve (Y53) - This part is responsible for choking the oil passage during tire vertical movement (cylinder retraction and extraction). By normal shock absorbers it is inside of it. The external damper valve allows changing its characteristics - rate of oil flow by electric operated valves. Nowadays it can be integrated within strut itself.

3. Pressure reservoir (4)- This part is hollow vessel filled with pressurized gas (b) separated from oil (a) by diaphragm. This ensures space for oil pushed from strut and its prompt return back to strut.

Distributor valve

Ditributor valve has 3 functions.

1. Oil delivery to all 4 struts- Oil is feed into all 4 struts under pressure. On front axle the load is higher and there are also return lines for oil passing around piston seals.

2. Additional oil delivery for leveling ADS is assuring vehicle is in same level no matter of load. This leveling is conrolled not electronically but mechanically by leveling valves.

3. Additional oil supply for raising vehicle By driver command via button next to headlight switch vehicle increase its ride height.

Distributor valve consist from several components.

Distributor block (52)- Is attached to right rail and all the oil lines are connected to it. It is casted part with drilled passages and one machined surface with passages to valve body.

Valve body (50)- Is attached to distributor body via four screws. The sealing between distributor and valve body is done with help of nine o-rings 4x1,8mm (inner diameter and diameter of profile). Its function is to allow oil flow from reservoir to struts via leveling valves and shut this flow when engine is off.

Lifting valve- Is attached to bottom of valve body via two screws. The sealing between lifting valve body and valve body is done with help of three o-rings 4x1,5mm and one 5x1,5mm. Its function is to allow flow of oil to link cylinders and from them. That is controlled via solenoid Y36 with two acting states and one default state. Also there is blocking valve solenoid Y37 which is directly energised and opened when ignition is on. Blocking valve is sealed via one o-ring 11x1,5mm and two 3,5x1,5mm. Lifting valve is not present on NA market vehicles.

Level valve

Level valve is routing oil to or from struts accordingly with vehicle situation. Level valve is fixed to car body. But operating lever is connected to suspension via link. This link transfer vertical movement of suspension as wheel bounces.

Link cylinder

For raising the vehicle there is a need to operate leveling valve independently from vehicle movements during the drive. So the link between suspension and lever of leveling valve is an actual small hydraulic cylinder. Normally it transfers vertical wheel movements from the torsion bar. When the driver wants to increase the ride height via a switch, another part of the distribution valve comes to play. It starts to push oil in these tiny cylinders. By its prolongation, these open leveling valves and vehicle raises by 30mm. These cylinders are double-acting, where one side prolongs in case of increased height and the second side shortens for sinking the ride for higher highway speed. That is true for the front axle. Leveling valve on the rear axle is mounted the way that the link cylinder acts oppositely. By its shortening, it raises the vehicle and by its prolongation, it lowers the car.
All materials are speaking about raising 30mm and lowering 15mm from "normal height". But in close look to link cylinder on cross-section right, you can see that "expansion" piston (b) has the near same travel lenght as "shrinkage" piston (c). I would assume expansion piston can travel 30mm and shrinkage 15mm. In rear should be just opposite, there are different part numbers front PN A1293200589, rear PN A1293200689. So let's think the drawing is not just.

Hydraulic oil reservoir

Reservoir (2) stores oil for ADS hydraulics. The standard level lies somewhere around half of its height and volume of it. There are both marks on the reservoir for minimal and maximal levels and also dipstick with the same marking. The rest of the volume is there for thermal expansion and excess oil during lowering the ride during high speed. It also contains a level sensor (S44) which lits MIL when volume falls down usually indicating a leak.
To be able open the cap you need to unscrew return line. On vehicles with ASD (locking differential), there is a second return line (T). Under the cap, there is basket-like filter catching debris if some get in hydraulic circuitry. There is also strong magnet to attract even the smallest metal particles.

Hydraulic pump

Vehicles with ADS have so-called tandem pump. That means besides creating pressure for power steering, there is also a second stage, creating pressure for ADS.
It is strongly recommended to keep the pump always running with enough oil to avoid any damage. When working on the vehicle, you will clearly notice the higher pitch noise when oil is missing.

Function

General info.

Hydraulics

Here is information about function of hydraulic components and some work done.

Electronics

Here is information about function of electronic components and some work done.

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