How to define BUSHING element in Adams correctly?

Hello, colleagues.

I have a question about proper bushing definition in Adams (especially in Car). Probably this issue have already solved many times, but it is still essential for modelling.

The question is: what is the right way to define active and reactive bodies in bushing? Some say that one should use the mechanism (say, vehicle suspension) topology and follow through it from part that give an excitation (a wheel, for example) to parts which react on this excitation. Also, there is an idea to consider I/J parts for bushing as inner/outer rings.

There is an issue when it comes to bushings with different radial stiffness. When you model such a bushing with different I/J parts order, you receive different results of bushing reaction. This difference may lead to different behaviour of related elements. I suppose it's related with bushing formulation described in the KB8013987 tech article.

For instance, there is a toelink, which has a bushing with different radial stiffnesses and a spherical joint. In this case different I/J parts order lead to different rotation of toelink around its axis and to different values of spherical joint working angle.

Thanks a lot for the explanation in advance

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0 viktor.kulagin over 4 years ago

JSlat, ilapakurti,

Thank you for your answers. But I can't agree with the point that it does not really matter.

Here is an example: a rear suspension toelink is connected with a subframe by a rubber bushing and with a knuckle by a spherical joint. Radial stiffnesses X and Y of the bushing are equal and symmetric. There are options of toelink/subframe bushing definition: in I/J order or in J/I order. Assume that general rules of bushing definition are unknown, so we can consider both options. Bushing property file stays the same for both options. Spherical joint doesn't get changed as well.

So, we perform parallel wheel travel simulation and get the following result (see the picture attached):

The upper 6 graphs show bushing deformation. Some of them show same results (symmetric relative to H graph axis), some of them differ. This difference leads to different spherical joint reaction (the lower 3 graphs), as it shows different rotation angles

In this very case this difference is crutial, as the maximum working (inclination) angle is both in the limit of working angle range (with one I/J order) and beyond the limit (with another I/J order).

You can check this with your models. I need to make it clear that this affects primary on bushing reaction (loads, deformation) and on link behaviour (rotation about axis following through joints); K&C properties can change in minor values.

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0 viktor.kulagin over 4 years ago

JSlat, ilapakurti,

Thank you for your answers. But I can't agree with the point that it does not really matter.

Here is an example: a rear suspension toelink is connected with a subframe by a rubber bushing and with a knuckle by a spherical joint. Radial stiffnesses X and Y of the bushing are equal and symmetric. There are options of toelink/subframe bushing definition: in I/J order or in J/I order. Assume that general rules of bushing definition are unknown, so we can consider both options. Bushing property file stays the same for both options. Spherical joint doesn't get changed as well.

So, we perform parallel wheel travel simulation and get the following result (see the picture attached):

The upper 6 graphs show bushing deformation. Some of them show same results (symmetric relative to H graph axis), some of them differ. This difference leads to different spherical joint reaction (the lower 3 graphs), as it shows different rotation angles

In this very case this difference is crutial, as the maximum working (inclination) angle is both in the limit of working angle range (with one I/J order) and beyond the limit (with another I/J order).

You can check this with your models. I need to make it clear that this affects primary on bushing reaction (loads, deformation) and on link behaviour (rotation about axis following through joints); K&C properties can change in minor values.

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