MoTeC Global Forum

Hello,
Any way to use gps speed ( 50hz high speed and acuracy GPS)
As vehicle speed on a 4wd aplication to be able to calculate slip? And also for launch rpm vs speed table? Or ecu already calculates vehicle speed through gps if this is the lowest speed?
Thank you

Hi,

As per the M1 Help, GPS will be used for Vehicle Speed if all Wheel Speeds are zero for greater than the Vehicle Speed Diagnostic Delay and that GPS Speed is greater than 10 kph.

We have done testing using GPS Speed for Launch Control, and there is just too much lag from the GPS signal for it to be usable. GPS Speed cannot be used for wheel slip calculations, unless you have individual wheel speed sensors in place, so that you can compare the wheel speeds versus the GPS Speed.

See Vehicle Speed State for the source of this value.

Vehicle Speed is derived from a number of sources, in the following priority:

Wheel Speed

If Brake State is:
•On: Vehicle Speed is the highest measured wheel speed.
•Off or Unknown or Sensor Fault: when Vehicle Drive Type is: ◦Rear: Vehicle Speed is the highest measured front wheel speed. If no front wheel speed sensor is available, Vehicle Speed is the lowest measured rear wheel speed.
◦Front: Vehicle Speed is the highest measured rear wheel speed. If no rear wheel speed sensor is available, Vehicle Speed is the lowest measured front wheel speed.
◦All: Vehicle Speed is the lowest measured wheel speed.



GPS

Used if all wheel speeds are zero for longer than Vehicle Speed Diagnostic Delay seconds and GPS speed is over 10km/h.

Estimated

Used if all wheel speeds are zero or faulty and GPS speed is not available. Calculated from Engine Speed, Gear Ratio Overall, Wheel Speed Rear Circumference and Wheel Speed Front Circumference.

Wheel speed sensors can also report a speed of 0km/h when the vehicle is stopped. To distinguish a stopped vehicle from faulty sensors all of the following conditions must be met for a time of Vehicle Speed Diagnostic Delay before the estimated value is used:
•Wheel speed sensors report zero or are not available
•Throttle Position is greater than Vehicle Speed Moving Throttle
•Engine Speed is greater than Vehicle Speed Stationary Engine Speed
•No fuel cut or ignition cut is effective
•Launch State is Disabled
•Anti Lag State is not Enabled