/RETRACTOR/SPRING

Block Format Keyword Define 1D retractor for seatbelt defined with material /MAT/LAW114 and property /PROP/TYPE23.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(8)
/RETRACTOR/SPRING/`retractor_ID`/`unit_ID`
`retractor_title`
`El_ID`	`node_ID`	`Elem_size`
`sens_ID`₁	`Pull_Lock`		`fct_ID`₁	`fct_ID`₂	`Yscale`₁	`Xscale`₁
`sens_ID`₂	`Typ_pre`	`Fmax`		`fct_ID`₃	`Yscale`₂	`Xscale`₂

Definition

Field	Contents	SI Unit Example
`retractor_ID`	Retractor identifier. (Integer)
`unit_ID`	(Optional) Unit identifier. (Integer)
`retractor_title`	Retractor title. (Character, maximum 100 characters)
`El_ID`	Element ID initially connected to retractor. (Integer, maximum 10 digits)
`node_ID`	Anchorage node ID. 1 (Integer)
`Elem_size`	Target element size for released elements. 4 (Real)	$[m]$
`sens_ID`₁	Sensor identifier for retractor locking. 3 (Integer)
`Pull_Lock`	Authorized amount of seatbelt release before locking. 6 (Real)	$[m]$
`fct_ID`₁	Function identifier defining loading force scale factor versus pullout when retractor is locked. 5 (Integer)
`fct_ID`₂	Function identifier defining unloading force scale factor versus pullout when retractor is locked. 5 (Integer)
`Yscale`₁	Retractor force. If `fct_ID`₁= 0: constant force (Default = 0) If `fct_ID`₁ ≠ 0: ordinate scaling factor for `fct_ID`₁ and `fct_ID`₂ (Default = 1). (Real)	$[N]$
`Xscale`₁	Abscissa scaling factor for function `fct_ID`₁ and `fct_ID`₂. Default = 1 (Real)	$[m]$
`sens_ID`₂	Sensor identifier used for pretension activation. 7 (Integer)
`Typ_pre`	Pretensioner type. 8 = 0 No pretension. = 1 Pretension is defined by pull in length versus time function. = 2 Pretension is maximum of force versus time function or retractor force. = 3 Pretension is maximum of force veruss time function or retractor force and `Pull_Lock` release. = 4 Pretension is sum of force versus time function and retractor force. = 5 Pretension is defined by energy versus time function. Default = (Integer)
`Fmax`	Maximum retractor force for pretensioner locking (for `Typ_pre` = 1 and 5 only). (Real)	$[N]$
`fct_ID`₃	Function identifier defining pretension as a function of time, force versus time, length versus time, or energy versus time. 8 (Integer)
`Yscale`₂	Ordinate scaling factor for function `fct_ID`₃. (Real)	$[N]$ , $[m]$ or $[J]$
`Xscale`₂	Abscissa scaling factor for function `fct_ID`₃. (Real)	$[s]$

Comments

The retractor is defined by 1 spring seatbelt element initially connected to the retractor and the node node_ID used to define the position of the retractor. The element El_ID must have a node initially at the same location as node node_ID. node_ID must not be a node of the seatbelt element.
Seatbelt spring elements can be initially positioned inside the retractors in order to be released during the run. These elements are automatically detected and deactivated until they are released from the retractor. This part of the seatbelt must be connected to element El_ID and the nodes of these elements must be at the same location as node node_ID.
The initial retractor force can either be defined by Yscale₁ if fct_ID₁=0 or by the 1^st point of the fct_ID₁(x=0) * Yscale₁.
When the retractor is unlocked, reference length of the element in the retractor is adjusted in order to ensure a constant force applied on the retractor.
When the element size in the retractor reaches Elem_size, a new element is released. In case there are no more elements to release, the last element in the retractor can continue to grow.

Figure 1.
The retractor is locked when the amount of seatbelt released reaches Pull_Lock value after the sensor sens_ID₁ activation.
When the retractor is locked, the force applied on the retractor is defined by fct_ID₁ and fct_ID₂. The force versus pullout is:
- For loading:(1)
  $F_{r e t r a c t o r} = Y s c a l e_{1} . f c t_I D_{1} . (\frac{L o c k e d_p u l l o u t}{X s c a l e_{1}})$
- For unloading:(2)
  $F_{r e t r a c t o r} = Y s c a l e_{1} . f c t_I D_{2} . (\frac{L o c k e d_p u l l o u t}{X s c a l e_{1}})$
The retractor can also act as a pretensioner when sensor sens_ID₂ is activated. The retractor applies force to pull the seatbelt inside the retractor:
- If Typ_pre = 1:
  The function fct_ID₃ defines the length of seatbelt pulled in as a function of time. In order to ensure that the effort on the seatbelt is not too high, the pretension is deactivated when the force in the retractor reaches Fmax.(3)
  $F_{t o t a l} = Y s c a l e_{2} . f c t_I D_{3} . (\frac{t}{X s c a l e_{2}})$
- If Typ_pre = 2:
  The function fct_ID₃ defines the pull-in force as a function of time. The total force in the element is the sum of maximum of the retractor force and the pretension force defined by fct_ID₃.(4)
  $F_{t o t a l} = \max . [F_{r e t r a c t o r}, Y s c a l e_{3} . f c t_I D_{3} (\frac{t}{X s c a l e_{2}})]$
- If Typ_pre = 3:
  The total force in the element is the same as Typ_pre = 2, but the seatbelt will be release by the value Pull_Lock before the retractor gets locked.
- If Typ_pre = 4:
  The function fct_ID₃ defines the pull-in force as a function of time. The total force in the element is the sum of the retractor force and the pretention force define by fct_ID₃(5)
  $F_{t o t a l} = F_{r e t r a c t o r} + Y s c a l e_{2} . f c t_I D_{3} (\frac{t}{X s c a l e_{2}})$
- If Typ_pre = 5:
  The function fct_ID₃ defines the pull-in energy as a function of time. Fmax can be defined to ensure the effort in the element is not too high and the pretension is deactivated when Fmax is reached. The pull-in energy being defined by:(6)
  $Y s c a l e_{2} . (f c t_I D_{3} . (\frac{t}{X s c a l e_{1}})) = \int_{t_p r e n t e n s}^{t} (F_{t o t a l} (t) . Δ_{p u l l i n} (t) d t)$
- When the pretension is deactivated, the retractor is also locked. The abscissa of the fct_ID₁ and fct_ID₂ is shifted in order to start at the pretension deactivation force value.
  
  Figure 2.
When a spring seatbelt element is in the retractor, viscosity is deactivated.
When a spring element is connected to a retractor its reference length $L_{0}$ is modified. In order to prevent the stiffness becoming infinite and the time step being too small in case of pull-in, a maximum value is used for the stiffness, computed from $L_{\min}$ defined in seatbelt material.(7)
$K = \frac{k}{\max (L_{\min}, L_{0})}$