Active suspension example

Objectives

In this example you will:

• Define DOE, Optimization and Monte Carlo studies.

• Run these studies.

• Plot graphs dedicated to design exploration.

• Do post-treatment specific to design exploration.

Results

The example deals with a very simplified car suspension. It is not intended to be a serious exercise on suspension design. However, it does illustrate the principles involved, is easy to understand and can be completed fairly quickly. We recommend you do this exercise first. The system is shown below.

Figure 1: An active suspension

The first step toward design exploration consists in selecting the inputs (the Simcenter Amesim model parameters) and the outputs (the Simcenter Amesim model variables) that you want to investigate.

Step 1: Get the system from the Simcenter Amesim demos

Procedure

1. Select Help > Get demo.

The Choose Demo dialog box appears.

2. Open the Tutorials folder and select ActiveSuspension.ame.

3. Click on Copy and open.

This demo is composed of two models of a car suspension:

• A passive suspension

• An active suspension

We will use the notation PS to stand for Passive Suspension and AS to stand for Active Suspension. Remember that the car drives over a "step" in the road of a height of 10 cm.

We consider two output quantities of each suspension model:

• The vertical acceleration of the car body.

• The compression of the spring which models the tire.

A high vertical acceleration of the car body is very uncomfortable for the vehicle passengers. It is desirable to have the acceleration less than 1 g = 9.81 m/s/s. The second quantity models the compression of the tire. A negative compression means that the tire is no longer in contact with the road.

This motivates two criteria:

Procedure

1. make the tire compression positive if possible, and

2. minimize the acceleration of the body.

We also consider that all the parameters are fixed excepted the damper rates which are allowed to vary.

Step 2: Run a simulation and plot the original curves

The original settings give the following results.

Figure 2: PS Body acceleration

Figure 3: PS Spring compression

The active suspension has initial values which make it identical to the passive suspension.

Step 3: Define parameters for the passive suspension

Procedure

1. Click the Study Manager button from the Simulation contextual toolbar.

Note You can also open the Study Manager in Parameter mode, using the Study parameters button .

2. Use drag and drop to define the Input and Simple output parameters as shown below.

Figure 4: Input parameters

Here, the rate of the PS damper is declared as being the input available for design exploration. This constitutes the design space. Figure 5: Simple output parameters

The two simple outputs declared will not be used directly. Remember we are not interested in the final values of these variables but rather in the maximum values of some of them and the minimum values of others. To do this we must define some Compound output parameters. Figure 6: Compound output parameters

3. We define:

a compound output as being the maximum value of the acceleration,

a compound output as being the minimum value of the compression.

These compound outputs correspond to the values marked in the figures Figure 2 to Figure 6. Our purpose in this section is to find a way to decrease the maximum body accelerations and to control the minimum tire compression.

4. Click Next to access the Studies tab.