Virtual Prototyping on May28 2010

by FSD | Print the article |

What is Virtual Prototyping?

Virtual Prototyping is defined as integrating a geometric model and related engineering tools such as analysis, simulation, optimization, and decision making tools, etc., within a computer-generated environment that facilitates multidisciplinary collaborative product development. In other words, its the use of computer simulation tools to test and analyze the performance of real systems. Virtual Prototyping will never, and should never replace physical testing but it can reduce the number of physical prototypes used throughout the product development process. It can also reveal all modes of failure where physical testing can usually only reveal one – the one that failed the prototype!

As we begin to see the light at the end of the tunnel in this economy, returning to profitability is of paramount importance to the decision makers in any company. In any business, a good way to increase profits is to reduce costs. The strength of Virtual Prototyping is the ability to:

Reduce product cost without a reduction in quality
Get products to market faster
Launch products on time
Meet quality targets at design release


The Cost of Testing

Think about how much it costs to test a new camshaft design. For some NASCAR teams it can add up to nearly $50,000 to test an engine on the dyno. That cost is only for testing – the test engine will never see the track! Why does it cost so much? In order to test an engine it must be built just like a race engine. It requires new pistons, rings, bearings, head gaskets, pushrods, valve springs, etc., etc… If that wasn’t enough, there’s the cost of the labor for someone to hone the block, CMM (Coordinate Measurement Machine) the pistons, balance the assembly if needed and assemble the engine. Add to that total the cost of dyno operators, racing fuel, oil and let’s not forget the teardown guys after the engine is all used up. I’ve left out many people/departments but you get the idea. What if the cam does not act the way it was designed? What if it doesn’t perform, or worse yet, it runs better but breaks retainers during durability testing? Now you’ve lost even more money! Cam testing for race teams can be very difficult and it is usually expensive.

Granted, usually test engines are not used for one single test. Normally several tests can be conducted on a fresh test engine. In addition to cam testing, other tests can be conducted such as cylinder head and intake manifold tests. Development Engineers for these race teams strive to get the most out of each test while the engine still has life in it and the results are believable, meaning the engine hasn’t lost power and still repeats well. Typically, in order to test one cam, three tests must be conducted:

1. Baseline cam test
2. Candidate cam test
3. Baseline repeat

If the baseline does not repeat then the results from the candidate cam are in question. If the baseline does repeat well then you can believe that the test was valid. Typically, around five cams are tested that are slight variations of the baseline. Out of those five, maybe one or two have enough merit to justify more testing or endurance testing in preparation for racing the design. Sometimes all five fail to deliver an improved power curve. This is a total loss in cam testing. Virtual Prototyping can help make sure this does not happen.


The Cost-Effective Solution

Virtual Prototyping can increase the chances of success and reduce the cost of testing. This procedure is also very efficient and can produce better results in less time than traditional methods. Although Virtual Prototypes can come in many forms, let’s look at high-performance, aftermarket cam design using Virtual Prototyping.

Explore the Design Space

Using Engine Simulation, the duration and lobe phasing can be determined in order to achieve the desired power goals. Using the existing cam as a baseline, lift and duration multipliers are used within the Engine model to simulate the increase/decrease of duration and lift of the cam. The intake and exhaust lobe phasing is also varied and the results of all the variables are recorded and analyzed in order to determine the cam specs that will deliver the desired power curve. Literally thousands of lift/duration/lobe phasing combinations can be tested in a few hours. Subsequent engine models will be created and used to design cams for different applications of the same engine. Such applications typically include:

Forced induction (Supercharged, Turbocharged)
Naturally aspirated
Stock engine – installing new cam in unmodified engine
Modified engine – installing new cam in a modified engine
Nitrous Oxide


Design, Run and Analyze the Virtual Prototype

Once the cam specs have been defined, a Valvetrain Simulation model is created and lobes are designed and tested until they meet the design criteria of the Engine Simulation model and do not exhibit any undesirable dynamic behavior. This iterative process continues until all goals of stability, durability and performance are obtained. The final prototype lift curves are then rerun in Engine Simulation to verify that they indeed perform as they were designed.

Manufacture and Test

After the design has been verified, the lobe data is sent to the cam grinder and a dyno test is scheduled. The likelihood of a positive outcome is ensured, especially in a street car application where performance is easy to predict with a high level of accuracy. Undesirable dynamic behavior has been minimized by designing the components to operate as a well designed system instead of a collection of components. Valvetrain behavior is typically dominated by valve spring frequencies and its harmonics as a function of speed. If any cLS7 Intake Rocker FEAomponent of the valvetrain system operates at a frequency near that of the valve spring then the valve spring can become excited when the two frequencies align. When that occurs bad things happen. Using simulation tools enables us to design around the natural frequency of the spring and select components that do not excite the spring. Additionally, we can choose a valve spring whose negative frequency characteristics lie outside the operating speed-range of interest.

Start Production

When properly done, Virtual Prototyping will lead to more productive testing. The big cost savings are in the fact that testing of candidate cams is reduced or eliminated except for design validation and durability testing. Components can be designed to use less material without sacrificing their structural integrity. In many cases, using the traditional method, cams are not even tested on a valvetrain test rig or dynamometer – they are sent to the track or the street based solely on the experience from previous designs. Although this is common practice among the big cam grinding companies, it is not a very efficient method when compared to Virtual Prototyping. Failure in any form of racing or street application can be very expensive! It is well proven that Valvetrain Simulation can accurately predict dynamic valve and spring behavior with very high accuracy in race applications. In comparison, high-performance street applications are far less volatile which also make them even more predictable. Using Virtual Prototypes to design the valvetrain components can allow manufacturers to reduce risk, shorten the design process (time and cost) and increase performance without sacrificing durability. Win, win, win, win.

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