Tài liệu Crankshaft Optimization Using Behavior Modeling Pro/ENGINEER Wildfire 2.0 pptx

Four basic studies will be performed on the crankshaft model: Sensitivity analysis allows you to analyze how various measured quantities parameters vary when a model dimension or an ind

The engine designer has a requirement to keep the crank in balance and an objective

of reducing the crank mass to enable quicker engine startup

Four basic studies will be performed on the crankshaft model:

Sensitivity analysis allows you to analyze how various measured quantities

(parameters) vary when a model dimension or an independent model parameter is varied within a specified range The result is a graph for each selected parameter showing the value of the parameter as a function of the dimension

This provides for understanding exactly how geometric changes to your model will affect your engineering goals or specifications

Feasibility and Optimization Studies

Feasibility and optimization studies allow you to have the system compute dimension values that cause the model to satisfy certain user-specified constraints

In a feasibility study, you define the following:

• A set of model dimensions to vary

• A range within which each dimension can vary

• A set of constraints that you want the design to satisfy

The analysis constraints are defined as equalities or inequalities that use parameters (which are the result of an analysis feature) and constant values A sample

constraint may appear as follows: length < 6.3 or distance = 11

To perform a feasibility study, the system does the following:

• The system attempts to find a set of dimension values within the specified ranges that satisfies all of the constraints

• If a solution is found, the model display changes to show these dimensions modified to the new values

You can either accept these new dimensions or undo the changes The model can be reverted to its state before the feasibility study There can be many solutions in a feasibility study that satisfy all constraint The system converges to one of the solutions

With an optimization study, you can specify the goal function in addition to the parameters for a feasibility study

In an optimization study, you define the following:

• A set of dimensions to vary

• A range within which each dimension can vary

• A set of constraints that you want the design to satisfy

• A goal function to be optimized (maximized or minimized)–a goal function is created as the result of an analysis feature

To perform an optimization study, the system does the following:

• The system looks for feasible solutions

• Out of feasible solutions, the system selects the solution that optimizes the goal function

The crankshaft has the following dimensions:

Step 1:

Create a 1.25 in diameter cylinder using FRONT datum plane as sketching plane The extrusion depth is 0.5 in Note that the center of the cylinder is 1.75 in above TOP datum plane

Step 2:

Create an extrusion for the balancing body of the crankshaft The dimensions of the section to be extruded are shown below The extrusion depth is 0.5 in

Under Edit pull down menu, select

Setup -> Mass Props

Enter density of steel as material of crankshaft

OK

ANALYSIS FEATURES

Click the Insert an analysis feature

icon The ANALYSIS dialog box appears Change the Name to be CG, and hit

Enter Choose Model Analysis Hit Next button to continue

Click the Compute button

Then choose Close

Parameters can be created for all the results of the analysis The can be used later in relations, in notes in drawing, or to drive optimizations

In this case, create a parameter for volume (by default)

Then click the Next button

Features can be created at the center of gravity (COG)

In this case create a point at the center of gravity

Select PNT_COG_ (e.g PNT_COG_282) Choose YES under Create

Click the Check button to finish The analysis feature CG is now in the model tree

Analyze the distance between the axis and point of CG

AXIS OF REVOLUTION

Datum point

at CG

Click the Insert an analysis feature

icon The ANALYSIS dialog box appears Change the Name to be OFFSET, and hit Enter

Make sure the Type of analysis is

Measure.

Hit Next button to continue

Under Type, choose Distance Next pick the datum point (e.g

PNT_COG_282) Then pick the axis (e.g A_4 axis) The Distance = 0.350236 is shown under Results

Click the Close button

Select Yes (under Create) to create a parameter for the distance

This is the offset from balance condition

Click the Check button to finish

Before we balance the crankshaft, we have one more condition must be satisfied

It is required that the balancing body

be at least 0.25 in larger than the shaft

The desired

Click the Insert an analysis feature

icon The ANALYSIS dialog box appears Change the Name to be SHOULDER, and hit Enter

Make sure the Type of analysis is

Measure.

Hit Next button to continue

Measure the distance between the edges

shown below Click the Close button

Click the Check button to finish

SENSITIVITY STUDIES

Sensitivity studies allow us to see how changing a model will affect our design goals

We select a given dimension to modify and describe the range through which it will move Pro/ENGINEER evaluates the model at intervals throughout the range of the variable and graphs one or more design parameters (e.g the offset distance vs the dimension)

Select Analysis pull-down menu

Then choose Sensitivity Analysis

The Sensitivity dialog box appears

Click the Dimension button

, select the balancing body feature to show dimensions, and choose the 3.000 dimension This is the height

of the axis of revolution to the bottom of balancing body of crankshaft

Change the range that the dimension will

The conclusions that can be drawn from the graphs:

• The shoulder distance is greater than 0.25 for the entire range of height values (2 – 3.2 inches)

• Offset distance as a function of the height between axis of rotation and

bottom of the balancing body Balanced at around 2.14 inches!

1 The crankshaft is balanced

2 The shoulder distance maintains a value of 0.25 in or greater

Select Analysis pull-down menu

Then choose

Feasibility/Optimization

The Optimization/Feasibility dialog box appears

Under Study Type/Name choose

Feasibility Add design constraints by selecting the

Make sure the Design Constraint as shown on the left

Click the OK button

Use the pull-down to change the

Parameter to

DISTANCE:SHOULDER Use the pull-down to change the = to

>= Toggle the Set option

Make sure the Design Constraint as

highlighted in red

Click OK

Select Options pull down menu, then choose Graph constraints

Choose Run tab

Click OK button

Choose Compute from

Optimization/Feasibility dialog box

HEIGHT

RADIUS

OPTIMIZATION STUDIES

The optimization study is setup very much like the feasibility study The main

difference is we can specify a goal This means that we not only arrive at a solution that works: we arrive at the best solution possible

In this case, we will set a goal of minimizing volume (and weight)

Fill out the Optimization/Feasibility dialog box as shown below, and click

Compute

23The resulting graphs:

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The model has been balance and optimized! Also the dimensions have changed as shown below Select Close to keep the dimensions, otherwise select Undo to return the model to its earlier state

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