Simcenter Madymo Simcenter Madymo - Dynamic locking tongue modelling

The principle of a dynamic locking tongue is to mechanically crimp the webbing portion passing through the tongue's slot at the buckle in a crash or emergency braking scenario so that the belt transfer from the shoulder belt to the lap belt is prevented. This is technically realized with a lock bar or a cam. The sketches below show the working principle of the dynamic locking tongue from ZF and Autoliv.

Fig. 1 - Patented DLT designs

Sources:

https://patents.google.com/patent/US8793844B2/en (ZF Passive Safety Systems Inc)

https://patents.google.com/patent/US20160206050A1/en (Autoliv Development AB)

Conceptually, such a crimping effect can be modelled in Madymo by virtually increasing the friction in the belt tying. Even if the FRIC_VEL_FUNC attribute is available in Madymo in the BELT_TYING element, the experience has shown that slip-stick issues can cause instability and noise on the signals. Therefore, the approach used in the demonstrator rather uses a force difference based control of the friction in the belt tying.

The dynamic locking tongue (DLT) model is defined in a separate SYSTEM.MODEL so that it can be easily glued to any existing buckle models. The DLT model itself is defined as an include and all positioning and design parameters as well as the initial settings are listed in the GROUP_DEFINE in the local SYSTE.MODEL.

Fig. 2 - Dynamic locking tongue Madymo MB model

The DLT can be copied and pasted in any model and connected to any buckle head by making use of the positioning parameters (attachment body, mounting position and orientation*).

*only Z-orientation is made available since the DLT is supposed to be plugged in/connected to a buckle head, which already has the correct 3D orientation. The parameter LT_MountRotZ is only meant to mirror the DLT if its design is not symmetrical for LH or RH implementation.

Fig. 3 - Positioning parameters

The available design parameters are the DLT mass, position of the centre of gravity, the inertial properties, DLT body height (excluding the metallic insert), the location of the tongue's slot w.r.t to the mounting location (top of the metallic insert). The stick activation parameter defines the force difference in N between the lap belt and the shoulder belt segments. The slip friction parameter defines the friction in the tongue in normal working conditions and the stick friction parameter represents the virtual crimping effect of the cam when the stick activation parameter value is exceeded.

Finally the initial settings enables to activate or deactivate the DLT and define the references of the respective belt segments of the existing belt to be used for the force difference calculation.

Fig. 4 - Design parameters and initial settings

Important: The crimping effect is mimicked by an evolutive friction function in the belt tying. The BELT_TYING element related to the tongue being defined in the BELT element which is not defined in the SYSTEM.MODEL of the DLT, the user must add a FRIC_FUN attribute with the value /LockingTongue_sys/Fric-in-tongue_vs_Time_fun to refer to the evolutive friction function. If any other FRIC_* attribute is already present in the BELT_TYING definition, such as FRIC_COEF, the user must delete those to avoid conflicts.

Fig. 5 - Update required in the BELT_TYING element modelling the tongue after implementation of the DLT

Note: for visual purposes, the cam rotation is made visible in the animation when the DLT activates but it does not effectively crimp the webbing!

The evolutive friction in the belt tying is managed by the CONTROL.SYSTEM as it follows:

• the solver always calculates the force difference between the lap belt and the shoulder belt segments at each time step
• a converter takes as input the above mentioned calculated value and returns the friction coefficient depending on;
  • if value < LT_stickactivation -> friction=LT_slipfric (normal working condition, DLT unlocked)
  • if 0.8*LT_stickactivation < value < LT_stickactivation -> friction linearly increases from LT_slipfric to LT_stickfric (transition phase)
  • if value > LT_stickactivation -> friction=LT_stickfric (webbing crimped, DLT locked)
• the result of the conversion is finally multiplied by a constant (0: DLT inactive 1: DLT active) depending from the defined LT_state parameter
• the FUNCTION.CONTROL_SIGNAL finally applies the friction to the belt tying. The function evolves in time but will remain always between LT_slipfric and LT_stickfric values. If LT_state equals zero, the FUNCTION.CONTROL_SIGNAL will remain constant to LT_slipfric whichever the calculated force difference is.
• the rotation of the cam is controlled in a similar way between 0° (open) and 20° (closed).
• a GROUP_MB LockingTongue_gmb containing the DLT envelop LockingTongue_Envelop_surf is also added for contact defintions with the surrounding parts such as the seat bolsters.

Please contact your local Simcenter Madymo support organization for further questions/details on this topic.