How can I modify the gear shifting logic of the HMMWV model for soft-soil terrain?

[ruibin]

Hello,

I am using the HMMWV vehicle model in Project Chrono for autonomous driving simulation on soft-soil/deformable terrain. 

 I found that on some soft-soil surfaces, the vehicle cannot track the target speed well with the default gear shifting logic. I suspect that the current shift strategy is mainly suitable for regular terrain, but may not work well on soft or deformable terrain because of terrain resistance and deformation. 

 So I would like to ask:

1. Is it possible to modify the gear shifting logic of the HMMWV model?

2. If yes, which code files or modules should I check?

3. If I want to design a custom shift strategy for soft-soil/deformable terrain, is there any recommended approach?

Thank you very much.

[Radu Serban]

 

The gear shifting algorithm depends on the transmission model you are using. The HMMWV model allows you to select from different options.

 

These schemes are implemented in the corresponding transmission mode templates, e.g., ChAutomaticTransmissionShafts, ChAutomaticTransmissionSimpleMap, ChAutomaticTransmissionCVT, etc., n their Synchronize function and depend on parameters of that transmission model.  For example, ChAutomaticTransmissionShafts uses shift bands defined by the upshift and downshift shaft RPM. For the HMMWV model these are set to 2500 and 1200, respectively (see HMMWV_AutomaticTransmissionShafts.cpp).

 

While we do not have perfect data for all parameters in our vehicle models, we consider these as being “fixed” for a concrete vehicle (like the HMMWV). If you want to change these, you will have to create your own HMMWV model (or just your own transmission model) and set them to whatever you want.

 

Alternatively, you can use a HMMWV model specified via JSON files (see the sample files under data/vehicle/hmmwv/), in which case you can directly set the upshift and downshift RPM values in the transmission JSON file (for example, HMMWV_AutomaticTransmissionShafts.json).

 

If you want a shifting algorithm different than what our templates have, you can also implement your own transmission template that uses whatever algorithm you want, by deriving from the base class ChAutomaticTransmission. Use as an example any of the existing transmission templates (e.g., ChAutomaticTransmissionShafts).

 

Hope that this helps,

--Radu

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