An ideal Continuously Variable Valve Duration model

Continuously Variable Valve Duration (CVVD) is a method to vary the valve duration of an internal combustion engine. Recently CVVD technology has been implemented by Hyundai in their 1.6 T-GDi engine. This post creates a representation of the system and examines the results of this model.

The model

The model is an ideal representation of the CVVD mechanism that is described in these youTube videos:

The World’s First CVVD Engine

World’s 1st CVVD Engine Technology: Improving Fuel efficiency, Performance while Reducing Emissions

The model in Figure 1. is not intended to be accurate it is only intended to exhibit the ability to vary the speed of the cam lobe.

Figure 1.  Simple CVVD model
Figure 1. Simple CVVD model

The CVVD consists of a disc which is located around the timing shaft. Within this disc there is a pivot which is connected by a slider to the timing shaft, and another pivot which is connected by a slider to the cam lobe pivot.

The location of the CVVD disc relative to the timing shaft is changed and this modifies the speed characteristics of the cam lobe.

Simulation results

Figure 2. Animation of the CVVD. The timing axle, the slider and pivot that is directly driven by the timing axle is blue. The pivot connected to the cam lob slider is green. The slider that is attached to the cam lobe is grey.

In Figure 2 the CVVDdiscPosition.s signal is the location of the CVVD disc relative to the timing shaft, this starts off at 5mm then at 10 seconds goes to 0mm and then goes to -5mm. The camPivot.w signal is the rotational velocity of the cam lobe.

The CVVD disc starts shifted to the left by 5mm. This results in the cam lobe rotating quickly when on the right side, due to the cam lobe slider pivot (the green part) having less distance to travel on the right to rotate the cam lobe through 180 degrees.

The position of the CVVD disc is centered at 10s resulting in the cam lobe speed being equal to the timing shaft. The CVVD disc is finally moved to the right by 5mm, resulting in the cam lobe rotating slowly when on the right side.

Implementing this CVVD mechanism in an engine model

This initial model contains a number of nonlinear systems of equations. Further work is required to reduce the number of nonlinear systems of equations before this CVVD system can be practically used in an engine model. This will be achieved through the use of aggregated joints and will be the subject of a future blog post.

Written by: Garron Fish – Chief Engineer

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