A torque transmission unit includes a first input side, a second input side, an output side, a hydrodynamic converter and a lock-up clutch. The first input side is configured to receive a first torque, and the second input side is configured to receive a second torque. The torque transmission unit has a freewheel. The freewheel is arranged downstream of the hydrodynamic converter, and the second input side is arranged downstream of the freewheel in a torque flow of the first torque from the first input side to the output side. The freewheel is designed to, in a first freewheel operating state, connect, in a torque-locking manner, the hydrodynamic converter to the output side for the transmission of the first torque from the first input side to the output side when the lock-up clutch is open. The freewheel is designed to, in a second freewheel operating state, decouple the hydrodynamic converter from the output side, to at least partially prevent a transmission of the second torque from the second input side into the hydrodynamic converter.

A hydraulic fracturing pump system may include a hydraulic fracturing pump, a gaseous fuel engine configured to drive the hydraulic fracturing pump, and a transmission system including a gear system mechanically coupled to the hydraulic fracturing pump and torque converter configured to fluidly couple the gaseous fuel engine and the gear system. The torque converter may include an impeller, a turbine fluidly coupled to the impeller and mechanically coupled to the gear system, a stator positioned between the impeller and the turbine, an impeller clutch configured to mechanically couple the impeller to the gaseous fuel engine, and a lockup clutch configured to mechanically couple the gaseous fuel engine and the gear system.

A vehicle control apparatus includes a lock-up control valve that controls a lock-up piston and a control system. A spool valve stem of the rock-up control valve is configured to move to an engagement position where working fluid is supplied to an apply oil path, a disengagement position where the working fluid is supplied to a release oil path, and the intermediate position. The control system is configured to perform a first starting control in which an engine is cranked in a state where the spool valve stem is held at the intermediate position and the clutch is engaged. The control system is configured to perform, when a start of the engine by the first starting control fails, a second starting control in which the engine is cranked in a state where the spool valve stem is moved to the disengagement position and the clutch is engaged.

A hydraulic fracturing pump system may include a hydraulic fracturing pump, a gaseous fuel engine configured to drive the hydraulic fracturing pump, and a transmission system including a gear system mechanically coupled to the hydraulic fracturing pump and torque converter configured to fluidly couple the gaseous fuel engine and the gear system. The torque converter may include an impeller, a turbine fluidly coupled to the impeller and mechanically coupled to the gear system, a stator positioned between the impeller and the turbine, an impeller clutch configured to mechanically couple the impeller to the gaseous fuel engine, and a lockup clutch configured to mechanically couple the gaseous fuel engine and the gear system.