Let's say that you are driving a Diesel Multiple Unit† with either mechanical* (i.e. an actual gearbox with multiple ratios) or hydraulic (i.e. two or more torque converters) transmission. When you move the “go faster” lever to a higher notch, what exactly is being commanded?
Possibilities that I can think of:
- Higher mass flow of fuel into the engine cylinders, whatever happens after that, happens
- Engine governor set to a higher rpm, whatever happens after that, happens
- Something else
This weirdly specific question does relate to a question presented by a client, but I'm not being paid to solve it.
* Although unusual, and for a long time considered obsolete, there are still mechanical transmissions for this application in production. For example, the Voith DIWARail pack for small railcars, derived from a bus power pack, and I believe that ZF offer a similar solution.