ADD – concept and mode of operation
In tight curves, the leading bogie loses tractive effort. This loss can be minimized by exerting an active influence on the rotation angle of the leading bogie. The ADD develops an actuating force in tight curves that turns the bogie, and consequently the leading wheelset, away from the outside tracks, thereby reducing the guiding forces on the wheel flange.
In addition to reducing loss of tractive effort in curves, however, the main advantage of the ADD is in reducing maintenance costs for wheels and tracks. To keep maintenance costs as low as possible, a maintenance-free system was developed that actually achieves this goal in practice – and also has no drawbacks in the event of a failure. If a failure does occur, the ADD acts as a perfectly normal passive rotational damper.
ADD in a nutshell
Higher tractive effort in curves
Longer service life for wheel discs and curved track
Lower network access costs, when applicable
Conventional rotational damper and actuator highly integrated in a single component
Simple failsafe concept with the fallback solution of a conventional rotational damper
Autonomous, totally closed hydraulic system
Constructed from proven individual components
No closed-loop control – robust open-loop controller generates rotation angle-dependent actuating force
Operates at ambient temperatures as low as -40°C
Structure of the active rotational damper (ADD)
Each ADD has a double-acting cylinder hydraulically connected to a 4/3-way valve. On track that is straight or slightly curved, this valve in its center position achieves the characteristic of a conventional rotational damper. Its function as an active rotational damper takes effect in tight curves as of a preset curve radius.
Functioning of the active rotational damper (ADD)
In the case of smaller curve radii, individual changes in the length of the ADD inform a central electronic control unit as to whether a tight curve angles to the left or right. The control unit then sets the 4/3-way valve to the corresponding end position. This causes an electrically operated gear pump to apply high-pressure oil to the surface of either the piston or piston ring. The ADD generates a compressive or tensile force that is proportional to the rotation angle. The force couple arising between the locomotive body and the bogie increases the rotating motion of the leading bogie and reduces that of the trailing bogie, thereby reducing the guiding forces in curves.
The active rotational damper (ADD) is a fully closed, maintenance-free hydraulic system with a cylinder, control valve, valve block, hydraulic valves, position sensor, electromotor, pump, and oil reservoir. It is mounted on the existing damper brackets and connected to the car body using only pluggable electrical cables for the pump drive, valve control, and sensors. The retrofitted ADD component replaces the conventional rotational damper (two per bogie = "four per" locomotive).
In trial runs, the system has demonstrated a reduction in the quasi-static lateral force Y1,qst by 10 kN and an increase in tractive effort in the curve.