AutoSpring

The Spring carries the vertical load in a suspension, keeps the tire in contact with the road, and absorbs energy from road irregularities that would otherwise be transmitted to the vehicle and passengers.

The Spring free length and force verses deflection table are stored in an ADAMS/Car™ compatible property file. You select a Spring property file to determine the Spring properties. Example property files are provided in the MotionView installation at: $(ALTAIR_HOME)\hw\mdl\autoentities\properties\Springs

Spring Force

The Spring force is interpolated from the force-deflection table read from the property file using Akima’s method. When the Spring deflection is outside the range supplied in the property file, the Spring force linearly extrapolated.

Install Methods

The Spring install methods are used to ensure the springs carry the proper loads at the input position of the suspension. You can use one of three methods as summarized in the table below and in full detail in the following sections:

Points: The distance between Points 1 and 2 fixes the initial length of the Spring and hence its force. Any changes in the location of Points 1 and 2 affect the Spring’s length, initial force, and line of action. The initial length (l₀) of the Spring is:(1) $l_{0} = \sqrt{({(X_{p 2} - X_{p 1})}^{2} + {(Y_{p 2} - Y_{p 1})}^{2} + {(Z_{p 2} - Z_{p 1})}^{2})}$

Figure 1.
Length: Enter the length of the Spring to fix its load. Altering the locations of Points 1 and 2 changes the line the Spring acts along, but not the Springs initial length and force.

Figure 2.
Force: Enter the initial force in the Spring. Any changes in the locations of Points 1 and 2 only affect the Spring’s line of action. Further, changes to the Spring properties like free length and stiffness do not affect the initial force. At initialization of the solver an iterative method is used to determine the Spring length that yields the entered force.

Force and Displacement Scaling

F_s = VG_s(H(L₀-d))

Where,

F_s: Spring force
V: Force scale
G_s: Akima interpolation function
H: Displacement scale
L₀: Spring free length
d: Instantaneous Spring length

Spring Properties

The Spring properties are stored in a AutoSpring text file. When you submit your model to the solver, the solver reads the Spring properties file for use during the simulation. If the units in the Spring properties file differ from the model, the solver internally converts the Spring properties to model units. The properties file is unchanged.

The Spring properties file contains header, units, spring data, and curve blocks. The units block specifies the length, mass, force, time and angle units employed in the file. The spring data block holds the spring free length. The curve block holds table of deflection and force values.

Sign Convention

Positive displacement in the Spring is compression. While positive force acts to push apart the two bodies the Spring connects. Thus when plotted the force (Y) vs. displacement (X) curve should lie in the first and third quadrants.

An example TeimOrbit format spring properties text file is shown below:

$--------------------------------------------------------------------HEADER
[HEADER]
FILE_TYPE     =  'spr'
FILE_VERSION  =  4.0
FILE_FORMAT   =  'ASCII'
$---------------------------------------------------------------------UNITS
[UNITS]
LENGTH =  'mm'
ANGLE  =  'degrees'
FORCE  =  'newton'
MASS   =  'kg'
TIME   =  'second'
$---------------------------------------------------------------SPRING_DATA
[SPRING_DATA]
FREE_LENGTH  =  270.75
$---------------------------------------------------------------------CURVE
[CURVE]
{ disp    force}
-300.0 -15000.0
-200.0 -12000.0
-150.0  -9000.0
-100.0  -6000.0
 -50.0  -3000.0
 -10.0   -600.0
   0.0      0.0
  10.0    600.0
  50.0   3000.0
 100.0   6000.0
 150.0   9000.0

Connecting an AutoSpring

Connections define the two bodies that the Spring connects and the two points that fix the line of action of the Spring force. The Spring acts on Body 1 at Point 1 and on Body 2 at Point 2.

From the Connectivity tab, select the first body to connect.
- Click Body 1 and select a body from the modeling window.
- Double click Body 1 and select the required body from the dialog.
Similarly, select the second body to connect by clicking the Body 2 input collector.
Select the first point.
- Click Point 1 and select a point from the modeling window.
- Double click Point 1 and select the required point from the dialog.
Similarly, select the second point.

Select an install method.

Option	Description
Points	Select the Points radio button to use the distance between Points 1 and 2 as the initial length of the Spring. This is the typical choice when the points are located at the center of the upper and lower Spring seats as shown in the figure below: Figure 3.
Length	Enter the length of the Spring at the input position of the Point 1 and Point 2. For example, if your suspension employs a Spring coil over damper arrangement you might use the upper damper and lower damper points to fix the line of action of the Spring (see the figure below). However the distance between these points is much greater than the length of the Spring, therefore the Spring force will not be correct. So select length and enter the actual length of the Spring. If the locations of Point 1 and Point 2 change, the initial Spring length remains the value you entered. Figure 4.
Force	Enter the initial force in the Spring at the input position. Changes to the locations of Points 1 and 2 and to the Spring properties do not alter the force. The solver computes the initial Spring length that yields the entered force during the initialization phase prior to any analyses. The solver always computes the initial Spring length prior to any in order to account for all changes in the point positions or the Spring properties.

Check the Output box to add an output request for the Spring length, length-rate-of-change, the Spring force, and the direction cosines of the line passing through Point 1 and Point 2.
The Spring length and length-rate-of-change is measured along the line between Point 1 on Body 1 and Point 2. The Spring force also acts along the same line. A positive Spring force acts to repel the bodies, while a negative Spring force acts to attract the bodies.

AutoSpring Output Channels

The output channels in the MotionSolve .mrf file are summarized below:

Table 1.
Type	Component	Quantity
REQSUB	RESULT(2)	Spring length
	RESULT(3)	Rate-of-change-of-spring-length.
	RESULT(4)	Spring force.
	RESULT(6)	Global X direction cosine of Spring.
	RESULT(7)	Global Y direction cosine of Spring.
	RESULT(8)	Global Z direction cosine of Spring.