| Transmission types |
|---|
|
|
|
|
|
|
|
|
|
|
Dynaflow was the trademark name for a type of automatic transmission developed and built by General Motors' Buick Motor Division from the late 1940s to the mid 1963.[1] The Dynaflow, which was introduced for the 1948 model year only as an option on Roadmaster models, received some severe early testing in the M18 Hellcat tank destroyer, which were built in Buick's Flint, Michigan assembly plant during World War II. It was also used in the 1951 Le Sabre concept car.[2]
The Dynaflow initially used a five-element torque converter, with two turbines and two stators, as well as a planetary gearset that provided two forward speeds plus reverse. In normal driving, Dynaflow started in high gear (direct drive), relying on the converter's 2.1:1 torque multiplication to accelerate the vehicle. Low gear, obtained via the planetary gearset, could be manually engaged and held up to approximately 40 mph (64 km/h), improving acceleration. However, the transmission was incapable of automatic shifting, requiring the driver to move the shift lever from low to drive to cause an upshift. Buicks equipped with the Dynaflow transmissions were unique among American automobiles of the time in that the driver or his/her passengers would not detect the tell-tale interruption in acceleration that resulted when other automatic transmissions of the time shifted through their gears. Acceleration through a Dynaflow was one smooth (if inefficient and slow[3]) experience. It was because of this slow shifting that the Dynaflow transmission was nicknamed "Dynaslush."[4]
The Dynaflow was an inherently inefficient design due to its sole reliance on the torque converter in normal driving. Exacerbating the situation was the dual stator arrangement, which wasted more power than the simpler three element converters used with other automatic transmissions, such as Chrysler's TorqueFlite. The multiple stators increased turbulence in the converter, even when operating in the coupling phase.
In 1953, Buick redesigned the Dynaflow, calling it the Twin Turbine Dynaflow. The converter now incorporated two turbines and a planetary gear set, but only a single stator. The first turbine was linked to the ring gear and the second to the planets, which gave a 2.5:1 torque multiplication which was now partly mechanical. This resulted in better efficiency especially at highway speeds as well as a higher level of performance and no penalty regarding the trademark smoothness. Buick also incorporated a variable-pitch stator in 1955 for greater flexibility. While these changes improved the transmission's overall performance and efficiency, the Dynaflow still was no match for other designs that utilized three element converters with automatic shifting.
A new version appeared in 1958: the Triple Turbine (Flight Pitch Dynaflow)3-speed.[3] This unit was similar to the Twin Turbine, but bore some operational differences, amongst them a variable pitch stator that increased converter's torque multiplication to 3:1. The stator element of the torque converter has two blade positions, controlled by the driver via the accelerator pedal to offer a 'passing gear' and extra response at any speed from heavy throttle application. In normal driving the stator blades are arranged at 'cruise' angle which offers improved efficiency and response at light throttle. Flooring the accelerator pedal changes the angle of the stator vanes hydraulically to 'performance angle' which permits the converter to achieve stall about 1000 rpm higher than in 'cruise' as well as redirecting oil to strike the next-lowest drive turbine which effectively lowers the drive ratio of the transmission and allows engine speed to flare to a speed where output is greatest. A few identifying features: the older Twin Turbine model was fitted with a rear pump, which meant the vehicle could be push-started (considered a desirable feature at the time). Also, the Twin Turbine would allow engagement of low gear up to 40 mph (64 km/h), and had a shift quadrant that read P-N-D-L-R. In contrast, the Triple Turbine unit did not have a rear pump, so it could not be push started, as there was no means to produce line pressure to engage any friction elements. It would, however, allow engagement of low gear up to 45 mph (72 km/h), and had a shift quadrant that read P-R-N-D-G (where "G" stood for "grade retard").
In 1964, the Dynaflow was discontinued in favor of the more efficient Super Turbine 300 two-speed and Super Turbine 400 three-speed transmissions, Super Turbine 400 being Buick's trade name for the Turbo-Hydramatic. One feature of the Dynaflow, the variable-pitch torque converter stator, colloquially the "Switch-Pitch", lived on in some versions of the Turbo-Hydramatic (Super Turbine 400) fitted to full-size Buicks, full-size Oldsmobiles and Cadillacs built from 1964–1967, as well as the Buick Super Turbine 300 and Oldsmobile Jetaway.
The early 1950s Cadillacs were normally equipped with Hydramatic transmissions. However in 1953 the General Motors Hydramatic Plant burned to the ground, leaving Cadillac without a source of transmissions. Buick Dynaflow transmissions were hastily adapted to Cadillac mount points, and some 19,000 1953 Model 62 Cadillacs, and some 28,000 Cadillacs of all models, were equipped with Dynaflow transmissions. Several thousand 1953 Oldsmobiles were also equipped with Dynaflow.