Automatic for the People

B R E A K T H R O U G H S T H AT D I D N ’ T

Turbine-Powered Cars If it’s the jet age, why doesn’t a car have a jet engine? After a decade or so of work, Chrysler released the Turbine Car in the Sixties, building five prototypes and 50 vehicles for the public to test. The technology worked and offered advantages in durability and maintenance, but the car was noisy, relatively slow, and poor on fuel economy. By the Eighties, Chrysler permanently grounded the idea of a jet-powered car. THE FIRST MAINSTREAM automatic transmission, the General Motors Hydra-Matic, is easily one of GM’s greatest contributions to autodom. Using simple mechanics, complicated math, and incredible production standards, the company introduced a technology that would not be fully mastered until decades after its 1939 debut.

These days automatic transmissions equip about 99 percent of new vehicles sold in the U.S., a dominance achieved thanks to undeniable advantages. Compared with any manual transmission, today’s automatics are easier to use, as reliable, and often faster and more fuel efficient. This ease changed the world. By making cars almost effortless to drive, GM spawned the large American cruisers that reshaped our highways and enabled rampant suburbanization.

Some feared the Hydra-Matic was too complicated a machine to ever be reliable. It proved its durability, though. When World War II paused all consumer automotive production in the U.S., Cadillac put Hydra-Matic transmissions into M-5 light tanks—helpful for the war effort and later for the postwar marketing folks. Confidence in the Hydra-Matic soared. The breakthrough autobox stayed in production for decades and cemented the automatic transmission as a must-have option for almost all consumer cars.

A. The input shaft connects to the engine, turning even when the brakes are holding the car.

Manual transmissions solve this by requiring the driver to engage the clutch, but the technology to automate this process in a reliable, compact consumer product did not exist.

Without something to mediate the relationship between input and output gears, a car would stall at every stop. B. The Hydra-Matic solved the stall issue with a simple fluid coupling. Rather than rotating a fixed gear shaft, the input rotates a container of fluid. This fluid transfers torque onto the output shaft but, importantly, can also simply spin around if the output shaft is locked in place. Later automatics added a stator that multiplies torque output. Those designs became known as torque converters.

F

AUTOMATIC FOR

THE PEOPLE GM’S HYDRA-MATIC IS REVOLUTIONARY, CONFOUNDINGLY COMPLICATED, AND RUGGED ENOUGH FOR WAR.

E D C A

C. A planetary gearset has one job: turn two input speeds into one output. The gearset has an outermost

“ring” gear, an innermost “sun” gear, and

“planet” gears that orbit between them.

The sun gear is the first input and, in this case, receives power from the fluid coupling. To output power, it transfers energy to the orbiting gears or the ring itself. D. A series of clutches, which connect input shafts to gearsets or hold ring gears in place, determines the route power takes through the transmission. Selectively engaging and disengaging them allows the car to choose from predetermined gear ratios. E. The ring gear is the second input—and a potential output—of a planetary gearset. A ring gear can be locked in place, spun naturally by the connection to the planet gears, or spun in time with a separate input shaft. Planetary gears output force onto a rotating planet carrier. Their final output ratio depends on the speed of both input gears. If the ring gear is stopped and the sun gear is moving, the planet carrier will rotate more slowly than the input speed but with a torque advantage. If the outer ring gear is spinning, the output speed increases, but the torque advantage diminishes. F. The path the power takes through all planetary gearsets determines the transmission’s final output. A reduced ratio in the first will affect the final output of the second, third, or fourth. Because of this and the multiple inputs that alter each gearset’s output, a

Hydra-Matic gearbox with two planetary gearsets can offer four forward ratios. A small gearset at the back of the transmission reverses flow to create reverse.

Simply choose Drive or Reverse on the gear selector and press the gas—the car handles the rest.