What does it mean when an engine is "direct drive"?

Question

Thank you.

Answer 1

one turn of the crankshaft = 1 turn of the pinion gear

Answer 2

The crankshaft is turning at the same revolutions per minute as the tail-shaft of the transmission. From that point on the drive shaft (exact rpm as the tail-shaft of the transmission) is coupled to a slip joint yoke to a universal joint. At this point a hollow drive shaft is connected to the rear end with another universal joint. Everything above is truly considered 1 to1 drive. However, something happens within the center section differential housing.
The pinion gear inside the rear end has scroll shaped teeth which turn at right angles the ring gear. Inside the rear end the number of teeth on the ring and pinion determine at what speed the axles turn in relation to the drive shaft. To get a better idea of the number of gear ratios available look up Ford 9" rear end gears.

Answer 3

A controlled direct drive engine efficiency uses positive-displacement power produced from a thermal energy source (or sources), which may include combustion energy. Engine power production is from a plurality of cylinders appropriately controlled by a hydraulic drive unit to add to or subtract from such power output to adjust cyclic variations, thus producing a desired velocity profile for a piston (or other mover) in a fluid-displacement cylinder that is being used to effect pumping (or compressing) of liquids, gases, or vapors. The overall system is particularly suited to use a Modified Brayton thermodynamic cycle where the power output is delivered through a common rod to a positive displacement fluid pumping or compressing device. Interconnected with that common rod is a double-acting hydraulic cylinder which is operated in conjunction with a rotary, variable volume hydraulic motor/pump to effect the desired adjustment. By using a plurality of power outputs from such a Modified Brayton cycle (or other cycle), which outputs are phased to operate complementary to one another, power is transferred between individual power outputs to efficiently and smoothly operate a plurality of fluid-displacement devices.