1. Vehicle Suspension Explained by Bond Graph Modeling Justin Otero ME270 CSUS MSME Program Fall 07

2. Topics  Objectives  Vehicle Suspension Overview  Bond Graph Models  Results  Conclusion

3. Objectives  Model Vehicle Suspension in CAMPG, MATLAB and SIMULINK.  Come up with Design parameters to optimize vehicle ride quality.

4. Vehicle Suspension  The suspension represents an important part of the ride quality.  Without suspension, a vehicle acts in a stiff and uncomfortable way.  Suspension system consists of a spring, a damper and the tire.  By creating a system model, a car manufacturer is able to see how the stiffness of the springs affects the ride experience.

5. Vehicle Suspension Typical Diagram of a Vehicle Suspension system Picture from www.Britannica.com

6. Suspension Diagram Vehicle Mass, M1 Spring, k1Damper, b Tire Center/Mass, M2 Ground Tire w/Air, k2

7. Bond Graph Model SF0 C:1/k2 1 I:M2 SE:M2g 0 1 C:1/k1R:b 1 SE:M1g I:M1

8. Results  This model simulates a vehicle with a mass of 1600kg hitting a bump traveling around 12.5m/s.  Values for the design criteria: Tire spring constant, k1 = 650kN/m Suspension spring constant, k2 = 250kN/m Suspension damper constant, b = 10,000kg/s  The first graph shows how the tire compresses, then the suspension takes affect and buffers the impact.  The second graph shows how the vehicle body reacts as the suspension compresses at first, then returns to normal.

9.  From these graphs, it’s seen that the tire compresses no more than 3cm and the total vertical distance the vehicle is displaced is no more than 10cm.

10. Conclusion  The bond graphs came out well with no causality issues and could be used to understand how a vehicle suspension system works.  Some other aspects could have been modeled in more detail (i.e. newer suspension systems contain sensors for traction control), and some variables (i.e. mass) were taken as estimates.  Due to time restrictions, other aspects that play a role in vehicle handling like the engine, transmission, brakes, steering and vehicle rotation had to be left out.