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0 - 1 © 2007 Texas Instruments Inc, Content developed in partnership with Tel-Aviv University From MATLAB ® and Simulink ® to Real Time with TI DSPs Vehicle Dynamics
Slide 2 © 2007 Texas Instruments Inc, Objectives To implement a simplified differential equation for the motion of a car. To build and test a Simulink Model. To run the model in real-time using the ezDSP F2812 hardware.
Slide 3 © 2007 Texas Instruments Inc, Motion of a Vehicle Consider the case of a car driving in a straight line along a flat road.
Slide 4 © 2007 Texas Instruments Inc, Engine Power The driving force is supplied by the engine. Engine Power
Slide 5 © 2007 Texas Instruments Inc, Vehicle Weight The weight of the vehicle will need to be overcome to move the vehicle. Vehicle Weight
Slide 6 © 2007 Texas Instruments Inc, Wind Resistance As the car moves, there will be wind resistance. WindResistance
Slide 7 © 2007 Texas Instruments Inc, Vehicle Speed The engine power, vehicle weight and wind resistance determine the vehicle speed. Vehicle Speed
Slide 8 © 2007 Texas Instruments Inc, Combined Factors These factors can be brought together into an equation of motion. b.v m F v
Slide 9 © 2007 Texas Instruments Inc, Differential Equation F = m.dv/dt + b.v where: –F = force provided by the engine –m = mass of vehicle –dv/dt = rate of change of velocity (acceleration) –b = damping factor (wind resistance) –v = velocity (vehicle speed)
Slide 10 © 2007 Texas Instruments Inc, Transformed Equation To implement the equation using Simulink, the equation needs to be first transformed. F/m –v.b/m= dv/dt We will set up a subsystem with: – Force F as the input. – Speed v as the output.
Slide 11 © 2007 Texas Instruments Inc, Continuous Implementation Using Simulink, the equation can be implemented as a continuous system as shown in the diagram. To generate v, we need to integrate the acceleration dv/dt.
Slide 12 © 2007 Texas Instruments Inc, Simulink Model
Slide 13 © 2007 Texas Instruments Inc, The Simulink Model The model of vehicle motion is shown below:
Slide 14 © 2007 Texas Instruments Inc, Description of Model The input to the system is the gas pedal, under control of the driver. The Engine Management sub-system converts gas pedal to engine power. The Vehicle Dynamics sub-system converts engine power to vehicle speed. The output is provided in horsepower.
Slide 15 © 2007 Texas Instruments Inc, Engine Management Subsystem This converts the gas pedal input (0-100%) to engine output power (0 – 200 hp).
Slide 16 © 2007 Texas Instruments Inc, Lookup Tables The conversion from rpm to power can be implemented using a lookup table.
Slide 17 © 2007 Texas Instruments Inc, Lookup Table Curve The table values can be adjusted to fit a smooth curve.
Slide 18 © 2007 Texas Instruments Inc, Vehicle Dynamics Subsystem To implement the equation of motion on the C28x, a Discrete Time Integrator is required.
Slide 19 © 2007 Texas Instruments Inc, Running the Simulation The ramp generator gently changes the Gas Pedal from 0% to 100%. This simulates smooth acceleration.
Slide 20 © 2007 Texas Instruments Inc, Tuning the Model Alter the mass m of the vehicle between 1 ton (for a small compact car) and 35 tons (for a truck). Increase the wind resistance by increasing variable b. Using real data from a car manufacturers website for the Lookup Table. You could also profile a diesel engine. Replace the Ramp input with a Step input to simulate stamping on the gas pedal!
Slide 21 © 2007 Texas Instruments Inc, Introduction to Laboratory
Slide 22 © 2007 Texas Instruments Inc, Overview of Laboratory The Simulink model will be modified to run on the ezDSP F2812 hardware. A potentiometer will be used to simulate the gas pedal. The output speed of the system will be monitored using a multi-meter.
Slide 23 © 2007 Texas Instruments Inc, Modifications for C28x To run on the ezDSP F2812, additional blocks from the Embedded Target for TI C2000 DSP are required.
Slide 24 © 2007 Texas Instruments Inc, ADC Scaling The ADC input 0- 4095 needs to be scaled 0- 100%. Using fixed-point math, this can be implemented as multiply by 800 then divide by 32768.
Slide 25 © 2007 Texas Instruments Inc, DAC Scaling The input 0-200 kph needs to be scaled 0-62500 for the DAC.
Slide 26 © 2007 Texas Instruments Inc, References ezDSP F2812 Technical Reference.
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