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09
Sep

VSB14 Suspension Simulation

We’ve recently been doing some assessments of various suspension systems to show that they meet guidelines set out in VSB14. So, what is VSB14? VSB stands for Vehicle Standards Bulletin and VSB14 forms the National Code Of Practice (NCOP) for light vehicle construction and modification. This is essentially a set of technical guidelines that cover various forms of modifications to production cars and the construction of kit cars or Individually Constructed Vehicles (ICV). It outlines what modifications can be made without an engineer’s certificate, and those that require a certifying engineer to sign off on them. The NCOP is now being adopted by various states across Australia as the basis for approving light vehicle modifications for road registration and covers modifications to pretty much every aspect of the vehicle.

In terms of suspension design and modification, VSB14 sets out a lot of requirements which will need to be assessed by the certification engineer, such as workmanship, weld quality and the use of appropriate components. Whilst we are not signatories for signing off on vehicle modifications, we have been approached by certification engineers to perform assessments on various aspects of the suspension systems using computer simulation, which are otherwise difficult and time consuming to assess. The areas set out in VSB14 that we can assess in our simulation work include:

  • stress analysis of components
  • changes in toe, camber & track throughout the wheel’s range of motion
  • Ackermann angles
  • bump steer
  • roll steer
  • roll centre heights
  • joint operating angles
  • potential linkage overcentering

We use MBD and FEA to perform these assessments and recommend any changes that are needed to meet the requirements. The major advantage of using computer simulation to perform this work, is that it can all be done before any parts are even made. We can take a suspension system design, apply the loads set out in VSB14 and immediately find any weak spots or areas of concern. We then test and recommend changes to the design until the requirements are met. Similarly with suspension geometry, we can move the wheel through it’s full range of motion and make sure that geometry changes are acceptable and should contribute to predictable handling characteristics. All without needing any physical parts.

Even suspension systems that have already been made, will benefit from a ‘virtual’ assessment rather than a physical one. Not only are physical tests expensive and time consuming to set up with all the jigs, rigs, actuators and sensors, but there’s a very real chance that components will be damaged during the test. Some of the load cases in VSB14 are quite extreme and can cause parts to bend permanently, even if they are considered acceptable. So the cost of that physical test just went up again due to having to buy or fabricate new components. And then, once you’ve made any necessary design changes, you have to do it all over again. Compare that to testing virtually on the computer screen, where calculated changes can be made and assessed immediately, with no damage to any existing parts, and it starts to make a lot of sense.

There are a few requirements for an accurate assessment. Firstly, we need to have accurate geometry that we can use in our software. If you’ve designed your parts using 3D CAD, then that’s ideal… we can directly import most CAD formats. If your suspension system has already been built, then it’ll need to be measured up and modelled in CAD. Another option for more complex parts is to get them scanned or digitised directly into a CAD file. The other major piece of information we need to know is what grade of material has been used. Whilst most suspension parts are generally made from steel, we need to know what grade or strength it is to know whether it will be strong enough. Test certificates from your steel supplier are ideal, and really should be something you have anyway. Other important information includes spring rates, bush stiffness, wheel sizes and offsets, shock travel, steering rack travel and bumpstop locations. It may take a bit of effort to gather all the necessary information, but once the model has been built, the test, assessment and revision process becomes a lot quicker and easier than any physical test.

If you would like to know any more about our suspension simulation work, have a look through our CAE Examples, or Contact Us directly with any questions you have.

About Brett Longhurst

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