Vehicle powertrain with a retarder and an expansion machine

The train has a vehicle drive motor for driving a motor vehicle by a vehicle drive shaft (2) that is propelled by the vehicle drive motor. A propellable or permanently drivable compressor (3) is arranged for compressing air for a pressurized-air system of the motor vehicle. The compressor is assigned to a drive-subsystem in the form of a steam-powered expansion machine (5), where the compressor is drivenable by the expansion machine.