How do nonlinear speedometers work?

Question

Some cars, now have nonlinear speedometers. How can they achieve to get different spacing between some speed ranges?

For better understanding, see the image

of an old Audi A4 speedometer.

The range from 70 to 100 is not linear, because there are equally spaced marks, as you can see in the table:

Mark        Increment from previous
  70               5 (was 65, not shown on this table)
  75               5 
  80               5 
  90              10
 100              10

score 9 · Accepted Answer · answered Feb 13 '16 at 16:41

The speedo will be a standard linear voltmeter.

Vehicle speed sensors are usually attached to either the gearbox output or the differential and produce a pulsed output at a frequency proportional to the vehicle speed.

On a 'normal' speedo, the ECU will read the pulses from the speed sensor and produce a linear voltage proportional to the vehicle speed to send to the speedo.

With this non-linear speedo, the ECU simply creates a non-linear voltage range that fits with the graduations on the speedo. This is a very simple task to perform in software.

How do nonlinear speedometers work?

1 Answers1