Dynamic Simulation : Cam Example Problem

1. Dynamic Simulation: • Cam Example Problem Objective • The objective of this module is to show how to add force joints to a model using the Dynamic Simulation environment in Autodesk Inventor software. • The specific example problem involves determining forces in various components of a boxer engine intake valve assembly, including springs, dampers and various types of contacts. • The Dynamic Simulation environment implements the theory covered in preceding modules.

2. System Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 2 cam • A cross section of the valve train components is shown in the figure. • The valve guide, lower spring plate, and valve guide seal are stationary. • The keepers, upper spring plate, cap, and tappet move as one assembly. • There is relative motion along the axis of the valve stem as the cam rotates and compresses the valve spring. tappet cap Keepers (keys) upper spring plate valve spring valve guide seal lower spring plate valve valve guide

3. Cylinder Block Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 3 • An artificial part (cylinder block) is created to simulate the cylinder head. • This part provides a flat surface for the lower spring plate to rest on and a cylindrical hole for the valve guide. • This part is grounded. Cylinder block

4. Cam Bearing Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 4 • Another artificial part is created to provide a fixed axis for the cam to rotate about. • This part is called the cam bearing. • The cam bearing is grounded. cam bearing

5. Assembly Constraints Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 5 • Inserts and mates are used to create positional constraints between the parts. • The grounded parts (cylinder block and cam bearing) provide fixed axes and surfaces that serve as starting points. • For example, a centerline mate exists between the valve and the valve guide.

6. Valve Spring Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 6 • The valve spring has the following properties. • Stiffness 15 N/mm • Free length 40 mm • Wire diameter 4 mm • The valve spring visibility is suppressed in the Assembly environment prior to going to the Dynamic Simulation environment. • The spring will be added as a force joint in Dynamic Simulation.

7. Dynamic Simulation Environment Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 7 The Dynamic Simulation environment in Autodesk Inventor software is entered by selecting the Dynamic Simulation icon that is seen when the Environments tab is selected.

8. Ground Constraints Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 8 • The information shown on the right is automatically created upon entering Dynamic Simulation. • Note that the Cam Bearing, Cylinder Block, suppressed valve spring, and Welded Group 1 are grounded. • Welded Group 1 consists of the valve guide, valve guide seal, and lower spring plate.

9. Mobile Groups Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 9 • There are two Mobile Groups: • Welded Group 2 contains the intake valve, upper spring plate, tappet, keepers (valve keys), and cap. • The second mobile group is the Intake Cam. • The Mobile Groups can be highlighted by right clicking on Mobile Groups in the browser and selecting Color Mobile Groups. Highlighted Mobile Groups

10. Standard Joints Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 10 • Two standard joints were automatically generated. • The first is a Revolution Joint that allows rotational motion about the cam shaft and cam bearing common axis. • The common axis is denoted by the arrow with three heads. Each part has a joint coordinate system. The green coordinate system is associated with the cam and the blue is associated with the bearing. The x-axis has a single arrow head, the y-axis has two arrow heads, and the z-axis has three arrow heads.

11. Standard Joints Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 11 • The second standard joint is a cylindrical joint between the second welded group and the first welded group. • The second welded group contains the valve and the parts that move with it. • A cylindrical joint allows translation and rotation about a common axis. • Note that the z-axis for both joint coordinate systems are aligned in the figure.

12. Gravity Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 12 • The direction and magnitude of gravity is set by double clicking on the gravity icon in the browser and selecting Vector Components. • In this problem gravity is acting in the negative-y direction. • An arrow indicating the direction will be displayed on the screen.

13. Valve Spring Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 13 • The valve spring is added as a Spring/Damper/Jack joint. • This option is found by right clicking on Standard Joints in the browser and selecting Spring/Damper/Jack.

14. Valve Spring Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 14 • A spring is created between the lower spring plate (Point 1) and the upper spring plate (Point 2). • A joint coordinate system is displayed for both parts with its origin at the points selected. • The z-axes for both coordinate systems are automatically oriented along the axis of the valve. • This is the only direction that the spring retainers can move in.

15. Valve Spring Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 15 • After selecting ok, the spring shown in the figure is created. • It does not have the correct geometry nor does it have the correct stiffness. • Note also that a Force Joints line is created in the browser. Spring

16. Valve Spring Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 16 • The correct spring geometry and stiffness is entered by right clicking on the Spring/Damper/Jack joint and editing the properties information. • Notice that the spring geometry now has a realistic appearance.

17. Cam & Follower Contact Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 17 • A 3D Contact joint is used to define the contact between the cam and cam follower. • This joint type is found by selecting the Standard Joints line in the browser, right clicking and selecting Add a Joint.

18. Cam & Follower Contact Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 18 • The top surface of the tappet is selected for Component 1. • The cam dwell surface is selected for Component 2. • Autodesk Inventor’s Dynamic Simulation knows that the contiguous lobe surface is part of Component 2. • A 3D contact joint is added to the Force Joint group in the Browser.

19. Cam Shaft Rotational Motion Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 19 • A performance boxer style engine is capable of crank shaft rotation speeds of 7,000 rpm. • The intake and exhaust cams will rotate at ½ of the crank speed or 3,500 rpm. • This converts to a cam shaft speed of 21,000 deg/sec. • Deg/sec are units needed on the next slide to define the motion.

20. Motion Constraint Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 20 Motion is applied by editing the properties of the Revolution Joint between the cam bearing and cam shaft. The motion is applied to the rotational DOF. Click the “Enable imposed motion box” to allow the velocity to be set.

21. Simulation Player Settings Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 21 • The simulation will be set to complete three revolutions. • At 21,000 deg/sec it will take 0.0171 seconds to complete a revolution or 0.051 seconds for three revolutions. • Solution data will be captured at each degree of rotation or 360 times per second. • This results in 1080 capture points. Click to perform simulation

22. Output Grapher Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 22 The output grapher is used to plot the computed results. The spring force is selected. Flat portion is the spring force during dwell. The negative value is due to the spring pre-load that is controlled by the spring’s free length. The spikes are due to the cam lobe depressing the spring.

23. Output Grapher Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 23 Multiple traces may be displayed at the same time. 3D Contact Force Spring Force

24. Float Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 24 • Float is realized when there is insufficient spring stiffness and/or pre-load to keep the cam and cam follower in contact. • Cam float can be seen in this problem by decreasing the spring constant to 3 N/m. • Cam float can also be affected by decreasing the spring pre-load or increasing the cam rotational speed.

25. Module Summary Section 4 – Dynamic Simulation Module 8 – Cam Example Problem Page 25 • In Module 6 of this section, the theory by which multi-body dynamic programs compute the forces acting between the bodies was presented. • This module provided an example of how to set-up and run a problem that computes forces in Autodesk Inventor’s Dynamic Simulation environment. • Assembly constraints were automatically converted to kinematic constraints while moving from the Assembly and Dynamic Simulation environments. • Additional constraints were implemented within the Dynamic Simulation environment.