How set differential gear ratio for Retarder

Question

I am looking to configure a Retarder for my vehicle but to obtain a slowing down of my vehicle, I have to set immense torque values.

When I look at the values returned in the script, I could see that the RPM calculation returns me a very small value.

Here is my current configuration:

rpm in Retarders.cs returns me around 300 rpm

Answer 1

The retarder brake sits between the gearbox output and the driveline input. This means that the rpm the retarder "sees" is the rpm of the wheels after passing through the driveline. In your configuration that is:

rpm at the retarder = average rpm at the wheels * 3.7 * 1 * 1

or 

rpm at the retarder = speed / wheel radius * 3.7 * 1 * 1 * 60 / (2*Pi)

The rpm at the retarder is also exposed in the Telemetry as "Transmission (rpm)". This is also the rpm at the output of the gearbox:

In your Retarder configuration, the problem are not the torque values but the RPM values. In this telemetry pic you can see that at 40 km/h (25 mph) the rpm at the transmission is 725. The differential gear ratio in this vehicle is 3.6, very close to yours. If we want the retarder to apply the maximum brake torque at 40 km/h and above, then the rpm values in this retarder should be 725.

Comments

Ok, I understand better how it works.

To configure the Retarder, it is therefore not necessary to rely on what is entered in Engine, but what the transmission returns to me in the Telemetry to have a good value.

Thank you for your quick reply.

---

That's correct.

In VPP the retarder brake doesn't depend of the engine. It still works with the gearbox in Neutral. Even a vehicle without engine could mount a retarder (i.e. a retarder brake in a trailer). This type of retarder is a "Secondary Retarder" (maybe it's named differently in your region). It acts on the driveline based on the speed of the wheels.

A different type of retarder brake is the "Primary Retarder", which is applied by special mechanisms in the engine itself. The primary retarder causes the engine to apply a friction based in the engine rpm, so the actual retarding torque reaching the wheels depends of the ratio of the currently engaged gear. This retarder needs a gear and the clutch not opening the transmission to operate.

In VPP the primary retarder may be simulated by modifying the parameters of the engine friction in runtime, so the engine would apply the retarding power.