| dbo:abstract
|
- Roto Hydramatic (sometimes spelled Roto Hydra-Matic or Roto-Hydramatic) was an automatic transmission built by General Motors and used in some Oldsmobile, Pontiac and Holden models between 1961 and 1965. It was based on the earlier, four-speed Hydramatic, but was more compact, providing only three forward speeds plus a small 8" fluid coupling with a stator inside of the fluid coupling (a type of torque converter, only integral with the transmission rather than being an independent unit). Oldsmobile, one of the companies that used this transmission in some of its cars, called the fluid couplings stator the "Accel-A-Rotor." The lightweight, aluminum-cased transmission was sometimes nicknamed the "Slim Jim." HydraMatic Division calls the Roto a four-range, three-gear HydraMatic. It counts the stator multiplication at 3.50:1 as a first gear, and when road speed and the two coupling halves’ speed match, it counts the same gear with fluid now passing straight through the stator as 2nd gear at 2.93 to one. Second gear (or third range) has a ratio of 1.56 , and because the fluid coupling is drained for this gear ratio, making the front clutch apply makes this a rare automatic that is in FULL mechanical lock-up (coupling drained) in second gear. Fourth range the coupling fills, releasing the front clutch makes a ratio of 1 to 1. This transmission, like single and dual range and dual coupling hydramatics, also has the feature of split torque in the transmission, whereby in fourth (or high) gear only 40% to 50% depending on transmission—-40% in Roto's case—-but because of the design the coupling is only required to carry 40% of the engine torque. The remaining 60% is in full mechanical connection, which made these Hydramatics the most efficient automatic until lock-up torque converter came into widespread use. Roto's disadvantage was the 2-3 range or 1-2 gear change because it is not only a huge ratio jump from 2-3 range or 1-2 shift from 2.93 to 1.56, but also there is no fluid slippage in the coupling because the coupling drains (four-tenths of a second) to engage or apply the front clutch and so the trans goes to full mechanical connection. The other disadvantage of Roto HydraMatic was the extreme oil pressures in the small 8" fluid coupling, which caused transmission leaks. All HydraMatic transmissions suffer some shift quality with today's ATF fluid. The original "Type A" fluid that these transmissions take is available only at O'Reilly Auto Parts. There were two models of the Roto Hydramatic: the lightweight Model 5, which weighed 145 lb (66 kg) and had ratios of 3.03, 1.58, and 1.00, and the larger Model 10, which weighed 154 lb (70 kg) and had ratios of 3.50, 2.93, 1.56, and 1.00. (en)
|
| rdfs:comment
|
- Roto Hydramatic (sometimes spelled Roto Hydra-Matic or Roto-Hydramatic) was an automatic transmission built by General Motors and used in some Oldsmobile, Pontiac and Holden models between 1961 and 1965. It was based on the earlier, four-speed Hydramatic, but was more compact, providing only three forward speeds plus a small 8" fluid coupling with a stator inside of the fluid coupling (a type of torque converter, only integral with the transmission rather than being an independent unit). Oldsmobile, one of the companies that used this transmission in some of its cars, called the fluid couplings stator the "Accel-A-Rotor." The lightweight, aluminum-cased transmission was sometimes nicknamed the "Slim Jim." HydraMatic Division calls the Roto a four-range, three-gear HydraMatic. (en)
|
