Simulink - Vehicle Acceleration 3 |
2. Setting up the Model
The one dimensional linear interpolation look up table is the most simple available in Simulink.
Values for the input are given and an equal number of values for the output must
be given, which can be by a mathematical relationship.
For this model, having dragged the block into the model window, move the
cursor over the block and click the right mouse button and click again on 'Lookup
parameters'. On the top line, within the [ ] brackets, the 13 engine speeds are entered:
As in the previous models the velocity is fed back and squared in the 'Dot Product' block to give v^{2} which goes through the gain block (Gain 3 = 0.4375) to give the opposing air resistance. The velocity is also fed back in a second loop and multiplied by 1/wheel radius (Gain 4) to give wheel angular velocity, by the gear ratio (Gain 5 = 10) to give the engine angular velocity and by 60/2*3.14159 (Gain 6) to give the engine rpm. This then goes into the look up table to generate the engine torque.
3. Results
Because only one gear is available in this model, the engine revs exceed
maximum (6000 rpm) after less than 4 seconds - however the look up table then
carries out a linear extrapolation beyond the highest stated engine rpm. The
time taken to reach 60 mph (26.4 m/s) of just under 5 seconds is not realistic
(the engine speed is over 8000rpm!).
David Grieve, 2nd November 2004.