Simulink - Vehicle Acceleration 3c


1. Brief Information
This model improves the realism of the gear change simulation by introducing a period of time (half a second) when zero torque is transmitted during the gear change.
The diagram is shown below:

2. Approach
Inserting a path with a simple time (transport) delay is not sufficient as this does not provide zero torque, which is what is needed to simulate the time between gears during a manual gear change. A multi stage operation is needed which involves more than a single switch.

The model above has 3 gears, the threshold for changing between them was set at velocities of 8m/s and 14m/s.

Following the lower track, through Gain2 (assumed overall first gear ratio) and Gain3, the net driving force signal is passing through the switch until the velocity exceeds 8m/s when the input is switched from the bottom to the top switch terminal which has zero input.
This zero value is then transmitted onward to and through Switch1.
Meanwhile at 8m/s the Relay is triggered and starts giving an output of 16. This is integrated by Integrator2 and after just over half a second this will have integrated up sufficiently to trigger Switch1 which has its threshold set at 8.1
Switch1 then passes the input from the top terminal, which is through the second gear path, via Gain (the overall 2nd gear ratio) and Gain4 with a transport delay of 0.5 seconds.
The same procedure is followed for the change from 2nd to 3rd gear, but the time delay incorporated in Transport Delay4 is 1 second, as this second gear change needs to include an additional half second delay.

Although little attempt has been made to accurately simulate the Porsche 944, the time for 0 - 60 mph comes out at about 7.5 seconds which is approximately 1 second slower than the published (conservative) 0-62.5mph time of 8.5 seconds.

David J Grieve, 16th February 2007.