Hydramatic
Encyclopedia
Hydramatic was an automatic transmission
developed by both General Motors' Cadillac
and Oldsmobile
divisions. Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first fully automatic mass-produced transmission developed for passenger automobile
use.
Cadillac, under Thompson, began working on a 'shiftless' transmission in 1932, and a new department within Cadillac Engineering was created, headed by Thompson and including engineers Ernest Seaholm, Ed Cole
, Owen Nacker
, and Oliver Kelley. During 1934, the Cadillac transmission group had developed a step-ratio gearbox that would shift automatically under full torque. This same group of engineers was then moved into GM Central Research, building pilot transmission units during 1935-36 which were then handed to Oldsmobile for testing.
The Automatic Safety Transmission (AST) was a tangent outgrowth of this work. The AST was a semi-automatic transmission using planetary gears
and a conventional friction clutch
, requiring the driver to use the clutch to shift into or out of gear, but not between the two forward gears. Oldsmobile offered the AST from 1937-1939, while Buick offered it only in 1938. The results were not quite what GM Research had in mind.
The HydraMatic was designed to combine hydraulic operation of a planetary gearbox (allowing much shifting to be automated) with a fluid coupling
instead of a friction clutch, eliminating the need for de-clutching. The transmission would have four forward speeds (3.82:1, 2.63:1, 1.45:1, and 1.00:1) plus reverse, with all acceleration provided by gearing; its fluid coupling did not multiply the engine output as a torque converter
does. (In this way, it was less sophisticated than the 1924 Vulcan prototype, which had a torque converter.) It incorporated a parking pawl which was engaged when the shift selector was placed in reverse with the engine off. There was no separate Park position as found with modern transmissions.
The result, dubbed "Hydra-Matic Drive," went into production in May 1939 for the 1940 model year
. The first Oldsmobiles so equipped were shipped in October 1939. Oldsmobile was chosen to introduce the Hydra-Matic for two reasons: economies of scale—Oldsmobile produced more cars than Cadillac at the time, thus providing a better test base—and to protect the reputation of Cadillac in case of a market failure of the new transmission. Advertising
proclaimed it "the greatest advance since the self-starter
."
In 1940, the Hydra-Matic was a $
57.00 option, rising to $100.00 for 1941. In 1941, it also became an option on Cadillac
s for $125.00. Almost 200,000 had been sold by the time passenger car production was halted for wartime
production in February 1942.
During the war, the Hydramatic was used in a variety of military vehicles, including the M5 Stuart tank
(where two of them were mated to twin Cadillac V8 engines) and the M24 Chaffee
light tank. The extensive wartime service greatly improved the postwar engineering of the transmission, later advertised as "battle-tested."
Starting in 1948 Hydramatic became optional for Pontiac
s (and was in 70% of them that year), although Buick
and Chevrolet
chose to develop their own automatic transmissions. One million Hydramatics had been sold by 1949. In the early 1950s various manufacturers without the resources to develop a proprietary automatic transmission bought Hydra-Matics from GM. Users included:
In 1952, Rolls-Royce
acquired a license to produce the HydraMatic under license for Rolls-Royce and Bentley automobiles. It continued production through 1967.
Evolving by the pressure of industrial competition from other manufacturers such as Studebaker's three speed lock up torque converter co-designed by Detroit Gear, named DG 200/250, and Packard
's dual range two speed lock up torque converter coupled Ultramatic
, GM's Hydramatic underwent several revisions through 1955, before being replaced by the substantially redesigned Controlled Coupling Hydramatic (also called Jetaway or dual-coupling Hydramatic) in 1956. The new four-speed transmission incorporated a secondary fluid coupling and a pair of sprag
clutches in place of the former friction clutch and brake bands, shifting in part by alternately draining and filling the secondary coupling. It allowed the driver to hold the transmission in second or third gear until the maximum allowable upshift points, for improved performance in traffic or in mountain driving, and incorporated a separate park position.
The Jetaway was substantially smoother than the original Hydramatic, but also more complex and expensive to produce, as well as less efficient. In 1961, a somewhat less complex, but also far less reliable three-speed Roto Hydramatic
also dubbed the "Slim Jim" Hydramatic (in which the "dump and fill" shifting principle was retained) was adopted for all Oldsmobiles as well as Pontiac's full-sized Catalina, Ventura, and Grand Prix models, while all Cadillacs and Pontiac's Bonneville and Star Chief models retained the older four-speed "Jetaway" unit (not to be confused with the two-speed Jetaway automatic used in various Buick, Olds and Pontiac intermediate cars from 1964-1969). Both of those Hydramatic transmissions were ultimately replaced by a new three-speed torque converter automatic transmission called Turbo-Hydramatic
in 1964 and 1965, whose design was more similar in principle to the Chrysler
TorqueFlite
and the '51 Borg Warner designed Ford Cruise-O-Matic
than the fluid coupling Hydramatic the "Turbo" replaced.
The original Hydramatic continued to be used in light trucks and other commercial vehicles well into the 1960s. It was subsequently replaced in that role by the Turbo-Hydramatic (THM), whose simplified design was much less costly to manufacture. Despite the name, the Turbo-Hydramatic has no mechanical relationship to the original Hydramatic.
The Hydramatic was a complex design that was expensive to produce. Despite some early problems, it was reliable, and so rugged it was widely used in drag racing
during the 1960s. It was not as smooth as some competitor's transmissions (notably Buick's Dynaflow
), but was more efficient, especially at highway speeds. The Hydramatic paved the way for widespread acceptance of automatic shifting.
A 3-speed light-duty version of the Turbo-Hydramatic called the Turbo-Hydramatic 180
was produced by GM's Hydramatic division from 1981 to 1998 for use in a wide variety of small cars and trucks.
Hydramatic is a trade name
for GM's automatic transmission division, which produces a variety of transmissions, the most notable of which is the Turbo-Hydramatic from the 1960s to the 1990s.
(not a torque converter
, which has at least three elements, the pump, turbine and stator) and three planetary gearsets
, providing four forward speeds plus reverse. Standard ratios for the original Hydra-Matic were 3.82:1, 2.63:1, 1.45:1 and 1.00:1 in automotive applications, and 4.08:1, 2.63:1, 1.55:1 and 1.00:1 in light truck and other commercial applications. The Jetaway Hydramatic used 3.96:1, 2.55:1, 1.55:1, and 1.00:1.
The Hydramatic was fitted with two pump
s to pressurize its hydraulic control system and provide lubrication of internal components. The front pump was a variable displacement vane unit driven from the fluid coupling housing, which meant oil pressure would be available immediately upon starting the engine. A relatively constant pressure was maintained by moving a slide inside the pump, which had the effect of changing the pump's displacement and therefore the volume of oil being delivered.
The rear pump was an unregulated spur gear type driven from the transmission output shaft, which meant it was capable of pressurizing the transmission if the vehicle was in motion. This feature made it possible to push-start a vehicle with a dead battery if the vehicle could be accelerated to at least 15–20 mph (24.1–32.2 km/h). At higher speeds, the rear pump provided all the oil volume that was needed to operate the transmission and the front pump's slide was nearly centered, causing that pump to produce little output.
In first gear, power flow was through the forward planetary gear assembly (either 1.45:1 or 1.55:1 reduction, depending on the model), then the fluid coupling
, followed by the rear gear assembly (2.63:1 reduction) and through the reverse gear assembly (normally locked) to the output shaft. That is, the input torus
of the fluid coupling ran at a lower speed than the engine, due to the reduction of the forward gear assembly. This produced an exceptionally smooth startup because of the relatively large amount of slippage initially produced in the fluid coupling. This slippage quickly diminished as engine RPM
increased.
When the transmission upshifted to second gear, the forward gear assembly locked and the input torus
now ran at engine speed. This had the desirable effect of "tightening" the coupling
and reducing slippage, but unfortunately also produced a somewhat abrupt shift. It wasn't at all uncommon for the vehicle to lurch forward during the 1-2 shift, especially when the throttle was wide open.
Upon shifting to third, the forward gear assembly went back into reduction and the rear gear assembly locked. Due to the manner in which the rear gear assembly was arranged, the coupling went from handling 100 percent of the engine torque to about 40 percent, with the balance being handled solely by the gear train. This greatly reduced slippage, which fact was audible by the substantial reduction that occurred in engine RPM
when the shift occurred.
The shift from third to fourth gear locked the forward gear assembly, producing 1.00:1 transmission. The fluid coupling now only handled about 25 percent of the engine torque, reducing slippage to a negligible amount. The result was a remarkably efficient level of power transfer at highway speeds, something that torque converter equipped automatics could not achieve without the benefit of a converter clutch.
Many Hydramatics did not execute the 2-3 shift very well, as the shift involved the simultaneous operation of two bands and two clutches. Accurate coordination of these components was difficult to achieve, even in new transmissions. As the transmission's seals and other elastomers aged, the hydraulic control characteristics changed and the 2-3 shift would either cause a momentary flare (sudden increase in engine speed) or tie-up (a short period where the transmission is in two gears simultaneously), the latter often contributing to failure of the front band.
From 1939-1950, the reverse anchor was used to lock the reverse unit ring gear from turning by engaging external teeth machined into that ring gear. From 1951 on, a cone clutch did the same thing when oil pressure was up, and a spring-loaded parking pawl was allowed to lock the same ring gear in the absence of oil pressure. This worked better as the anchor would not grind on the external teeth if that ring gear were turning (that is, unless the engine stalled as reverse was engaged). Reverse was obtained by applying torque from the front unit (band on, in reduction) through the fluid coupling to the rear unit sun gear. The planet carrier of this gearset was splined to the planet carrier of the reverse unit. The rear unit ring gear hub had a small gear machined on its end which served as the reverse unit sun gear. Because the rear unit band was not applied for reverse, the rear unit and reverse unit compounded causing the combined planet carriers to rotate opposite to the input torque and at a further reduced speed. The output shaft was machined onto the rear unit and reverse unit planet carriers.
Shutting off the engine caused the transmission oil pressure to rapidly dissipate. If the selector lever was in reverse or moved to reverse after the engine stopped, two mechanical parts combined to provide a parking brake. The reverse unit ring gear was held stationary by the reverse anchor. The drive shaft could still turn causing the reverse unit sun gear and attached rear unit ring gear to rotate at a very high speed, were it not for the fact that the rear unit ring gear band was now applied by a heavy spring. Usually, bands are applied by a servo
and released by spring pressure, but in this case, the band was held off by the servo and applied by spring pressure (actually, when the engine was running, the band was applied by a combination of spring pressure assisted by oil pressure). With the engine off, this brake band acting on the rear unit ring gear had a tremendous mechanical advantage. Since the rear unit ring gear with its attached reverse unit sun gear and the reverse unit ring gear were both locked to the transmission case, the planet carriers and driveshaft could not turn. As such, it provided an effective driveshaft mounted parking brake to be used alone or supplementing the hand brake.
Automatic transmission
An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...
developed by both General Motors' Cadillac
Cadillac
Cadillac is an American luxury vehicle marque owned by General Motors . Cadillac vehicles are sold in over 50 countries and territories, but mostly in North America. Cadillac is currently the second oldest American automobile manufacturer behind fellow GM marque Buick and is among the oldest...
and Oldsmobile
Oldsmobile
Oldsmobile was a brand of American automobile produced for most of its existence by General Motors. It was founded by Ransom E. Olds in 1897. In its 107-year history, it produced 35.2 million cars, including at least 14 million built at its Lansing, Michigan factory...
divisions. Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first fully automatic mass-produced transmission developed for passenger automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
use.
History
During the 1930s, automakers sought to reduce or eliminate the need to shift gears. At the time, synchronized gear shifting was still a novelty (and confined to higher gears in most cases), and shifting a manual gearbox required more care than most drivers cared to exert. The exception here was Cadillac's break-through synchromesh fully synchronized manual transmission, designed by Cadillac engineer Earl A. Thompson and introduced in the fall of 1928.Cadillac, under Thompson, began working on a 'shiftless' transmission in 1932, and a new department within Cadillac Engineering was created, headed by Thompson and including engineers Ernest Seaholm, Ed Cole
Ed Cole
Edward Nicholas Cole was an American automotive executive for General Motors.- Career :Cole was the son of a dairy farmer. In his youth, he designed, built, and sold homemade radio sets, and as a teenager became a field representative for a tractor manufacturer...
, Owen Nacker
Owen Nacker
Owen Nacker was an American automotive engineer.-Early Automotive Career:...
, and Oliver Kelley. During 1934, the Cadillac transmission group had developed a step-ratio gearbox that would shift automatically under full torque. This same group of engineers was then moved into GM Central Research, building pilot transmission units during 1935-36 which were then handed to Oldsmobile for testing.
The Automatic Safety Transmission (AST) was a tangent outgrowth of this work. The AST was a semi-automatic transmission using planetary gears
Epicyclic gearing
Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...
and a conventional friction clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
, requiring the driver to use the clutch to shift into or out of gear, but not between the two forward gears. Oldsmobile offered the AST from 1937-1939, while Buick offered it only in 1938. The results were not quite what GM Research had in mind.
The HydraMatic was designed to combine hydraulic operation of a planetary gearbox (allowing much shifting to be automated) with a fluid coupling
Fluid coupling
A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch...
instead of a friction clutch, eliminating the need for de-clutching. The transmission would have four forward speeds (3.82:1, 2.63:1, 1.45:1, and 1.00:1) plus reverse, with all acceleration provided by gearing; its fluid coupling did not multiply the engine output as a torque converter
Torque converter
In modern usage, a torque converter is generally a type of hydrodynamic fluid coupling that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load...
does. (In this way, it was less sophisticated than the 1924 Vulcan prototype, which had a torque converter.) It incorporated a parking pawl which was engaged when the shift selector was placed in reverse with the engine off. There was no separate Park position as found with modern transmissions.
The result, dubbed "Hydra-Matic Drive," went into production in May 1939 for the 1940 model year
Model year
The model year of a product is a number used worldwide, but with a high level of prominence in North America, to describe approximately when a product was produced, and indicates the coinciding base specification of that product....
. The first Oldsmobiles so equipped were shipped in October 1939. Oldsmobile was chosen to introduce the Hydra-Matic for two reasons: economies of scale—Oldsmobile produced more cars than Cadillac at the time, thus providing a better test base—and to protect the reputation of Cadillac in case of a market failure of the new transmission. Advertising
Advertising
Advertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...
proclaimed it "the greatest advance since the self-starter
Automobile self starter
A starter motor is an electric motor for rotating an internal-combustion engine so as to initiate the engine's operation under its own power.- History :...
."
In 1940, the Hydra-Matic was a $
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
57.00 option, rising to $100.00 for 1941. In 1941, it also became an option on Cadillac
Cadillac
Cadillac is an American luxury vehicle marque owned by General Motors . Cadillac vehicles are sold in over 50 countries and territories, but mostly in North America. Cadillac is currently the second oldest American automobile manufacturer behind fellow GM marque Buick and is among the oldest...
s for $125.00. Almost 200,000 had been sold by the time passenger car production was halted for wartime
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
production in February 1942.
During the war, the Hydramatic was used in a variety of military vehicles, including the M5 Stuart tank
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...
(where two of them were mated to twin Cadillac V8 engines) and the M24 Chaffee
M24 Chaffee
The Light Tank M24 was an American light tank used during World War II and in postwar conflicts including the Korean War and with the French in the War in Algeria and First Indochina War. In British service it was given the service name Chaffee, after the United States Army General Adna R...
light tank. The extensive wartime service greatly improved the postwar engineering of the transmission, later advertised as "battle-tested."
Starting in 1948 Hydramatic became optional for Pontiac
Pontiac
Pontiac was an automobile brand that was established in 1926 as a companion make for General Motors' Oakland. Quickly overtaking its parent in popularity, it supplanted the Oakland brand entirely by 1933 and, for most of its life, became a companion make for Chevrolet. Pontiac was sold in the...
s (and was in 70% of them that year), although Buick
Dynaflow
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...
and Chevrolet
Powerglide
The Powerglide is a two-speed automatic transmission designed by General Motors. It was available primarily on Chevrolet from January, 1950 through 1973, although some Pontiac models also used this automatic transmission, extensively on models produced for the Canadian market with Chevrolet...
chose to develop their own automatic transmissions. One million Hydramatics had been sold by 1949. In the early 1950s various manufacturers without the resources to develop a proprietary automatic transmission bought Hydra-Matics from GM. Users included:
- 1951–1953 HudsonHudson Motor Car CompanyThe Hudson Motor Car Company made Hudson and other brand automobiles in Detroit, Michigan, from 1909 to 1954. In 1954, Hudson merged with Nash-Kelvinator Corporation to form American Motors. The Hudson name was continued through the 1957 model year, after which it was dropped.- Company strategy...
- 1950–1953 NashNash MotorsAlso see: Kelvinator and American Motors CorporationNash Motors was an automobile manufacturer based in Kenosha, Wisconsin, in the United States from 1916 to 1938. From 1938 to 1954, Nash was the automotive division of the Nash-Kelvinator Corporation...
- 1951 FrazerFrazer (automobile)The Frazer was the flagship line of upper-medium priced American luxury automobiles built by the Kaiser-Frazer Corporation of Willow Run Ypsilanti, Michigan, and was, with Crosley, the first American car with new envelope body and fresh postwar styling.Named for longtime American automobile...
- 1951–1955 Kaiser
- 1954–1955 WillysWillysWillys was the brand name used by Willys-Overland Motors, an American automobile company best known for its design and production of military Jeeps and civilian versions during the 20th century.-Early History:In 1908, John Willys bought the Overland Automotive Division of Standard Wheel Company...
- 1949–1954 LincolnLincoln (automobile)Lincoln is an American luxury vehicle brand of the Ford Motor Company. Lincoln vehicles are sold mostly in North America.-History:The company was founded in August 1915 by Henry M. Leland, one of the founders of Cadillac . During World War I, he left Cadillac which was sold to General Motors...
In 1952, Rolls-Royce
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....
acquired a license to produce the HydraMatic under license for Rolls-Royce and Bentley automobiles. It continued production through 1967.
Evolving by the pressure of industrial competition from other manufacturers such as Studebaker's three speed lock up torque converter co-designed by Detroit Gear, named DG 200/250, and Packard
Packard
Packard was an American luxury-type automobile marque built by the Packard Motor Car Company of Detroit, Michigan, and later by the Studebaker-Packard Corporation of South Bend, Indiana...
's dual range two speed lock up torque converter coupled Ultramatic
Ultramatic
For the Voigtländer SLR camera, see Voigtländer Ultramatic CSUltramatic was the trademarked name of the Packard Motor Car Company's automatic transmission introduced in 1949 and produced until 1956 at Packard's Detroit, Michigan factory....
, GM's Hydramatic underwent several revisions through 1955, before being replaced by the substantially redesigned Controlled Coupling Hydramatic (also called Jetaway or dual-coupling Hydramatic) in 1956. The new four-speed transmission incorporated a secondary fluid coupling and a pair of sprag
Sprag
A sprag clutch is a one-way freewheel clutch. It resembles a roller bearing, but instead of cylindrical rollers, non-revolving asymmetric figure-of-eight shaped sprags are used...
clutches in place of the former friction clutch and brake bands, shifting in part by alternately draining and filling the secondary coupling. It allowed the driver to hold the transmission in second or third gear until the maximum allowable upshift points, for improved performance in traffic or in mountain driving, and incorporated a separate park position.
The Jetaway was substantially smoother than the original Hydramatic, but also more complex and expensive to produce, as well as less efficient. In 1961, a somewhat less complex, but also far less reliable three-speed Roto Hydramatic
Roto Hydramatic
Roto Hydramatic was an automatic transmission built by General Motors and used on Buick and on some Oldsmobile and Pontiac models from 1961-1964...
also dubbed the "Slim Jim" Hydramatic (in which the "dump and fill" shifting principle was retained) was adopted for all Oldsmobiles as well as Pontiac's full-sized Catalina, Ventura, and Grand Prix models, while all Cadillacs and Pontiac's Bonneville and Star Chief models retained the older four-speed "Jetaway" unit (not to be confused with the two-speed Jetaway automatic used in various Buick, Olds and Pontiac intermediate cars from 1964-1969). Both of those Hydramatic transmissions were ultimately replaced by a new three-speed torque converter automatic transmission called Turbo-Hydramatic
Turbo-Hydramatic
Turbo-Hydramatic is the registered tradename of a family of automatic transmissions developed and produced by General Motors. These transmissions mate a three-element torque converter to a Simpson planetary geartrain, providing three forward speeds plus reverse.The Turbo-Hydramatic series was...
in 1964 and 1965, whose design was more similar in principle to the Chrysler
Chrysler
Chrysler Group LLC is a multinational automaker headquartered in Auburn Hills, Michigan, USA. Chrysler was first organized as the Chrysler Corporation in 1925....
TorqueFlite
TorqueFlite
TorqueFlite is the trademarked name of Chrysler Corporation's automatic transmissions, starting with the three-speed unit introduced late in the 1956 model year as a successor to Chrysler's two-speed PowerFlite...
and the '51 Borg Warner designed Ford Cruise-O-Matic
Cruise-O-Matic
Ford-O-Matic was the first automatic transmission used by Ford Motor Company, designed by Borg Warner Corporation. Introduced in 1950, the three-speed Ford-O-Matic evolved into the Cruise-O-Matic in 1958 and the FMX in 1968. This line continued in production until 1980, when the AOD was introduced...
than the fluid coupling Hydramatic the "Turbo" replaced.
The original Hydramatic continued to be used in light trucks and other commercial vehicles well into the 1960s. It was subsequently replaced in that role by the Turbo-Hydramatic (THM), whose simplified design was much less costly to manufacture. Despite the name, the Turbo-Hydramatic has no mechanical relationship to the original Hydramatic.
The Hydramatic was a complex design that was expensive to produce. Despite some early problems, it was reliable, and so rugged it was widely used in drag racing
Drag racing
Drag racing is a competition in which specially prepared automobiles or motorcycles compete two at a time to be the first to cross a set finish line, from a standing start, in a straight line, over a measured distance, most commonly a ¼-mile straight track....
during the 1960s. It was not as smooth as some competitor's transmissions (notably Buick's Dynaflow
Dynaflow
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...
), but was more efficient, especially at highway speeds. The Hydramatic paved the way for widespread acceptance of automatic shifting.
A 3-speed light-duty version of the Turbo-Hydramatic called the Turbo-Hydramatic 180
Turbo-Hydramatic 180
Turbo-Hydramatic 180 was an automatic transmission developed and produced by General Motors. It was a light-duty derivative of the Turbo-Hydramatic and was manufactured and used in Europe and Asia in a variety of longitudinal engine vehicles...
was produced by GM's Hydramatic division from 1981 to 1998 for use in a wide variety of small cars and trucks.
Hydramatic is a trade name
Trade name
A trade name, also known as a trading name or a business name, is the name which a business trades under for commercial purposes, although its registered, legal name, used for contracts and other formal situations, may be another....
for GM's automatic transmission division, which produces a variety of transmissions, the most notable of which is the Turbo-Hydramatic from the 1960s to the 1990s.
Design
The Hydramatic used a two-element fluid couplingFluid coupling
A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch...
(not a torque converter
Torque converter
In modern usage, a torque converter is generally a type of hydrodynamic fluid coupling that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load...
, which has at least three elements, the pump, turbine and stator) and three planetary gearsets
Epicyclic gearing
Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...
, providing four forward speeds plus reverse. Standard ratios for the original Hydra-Matic were 3.82:1, 2.63:1, 1.45:1 and 1.00:1 in automotive applications, and 4.08:1, 2.63:1, 1.55:1 and 1.00:1 in light truck and other commercial applications. The Jetaway Hydramatic used 3.96:1, 2.55:1, 1.55:1, and 1.00:1.
The Hydramatic was fitted with two pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s to pressurize its hydraulic control system and provide lubrication of internal components. The front pump was a variable displacement vane unit driven from the fluid coupling housing, which meant oil pressure would be available immediately upon starting the engine. A relatively constant pressure was maintained by moving a slide inside the pump, which had the effect of changing the pump's displacement and therefore the volume of oil being delivered.
The rear pump was an unregulated spur gear type driven from the transmission output shaft, which meant it was capable of pressurizing the transmission if the vehicle was in motion. This feature made it possible to push-start a vehicle with a dead battery if the vehicle could be accelerated to at least 15–20 mph (24.1–32.2 km/h). At higher speeds, the rear pump provided all the oil volume that was needed to operate the transmission and the front pump's slide was nearly centered, causing that pump to produce little output.
In first gear, power flow was through the forward planetary gear assembly (either 1.45:1 or 1.55:1 reduction, depending on the model), then the fluid coupling
Fluid coupling
A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch...
, followed by the rear gear assembly (2.63:1 reduction) and through the reverse gear assembly (normally locked) to the output shaft. That is, the input torus
Torus
In geometry, a torus is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle...
of the fluid coupling ran at a lower speed than the engine, due to the reduction of the forward gear assembly. This produced an exceptionally smooth startup because of the relatively large amount of slippage initially produced in the fluid coupling. This slippage quickly diminished as engine RPM
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
increased.
When the transmission upshifted to second gear, the forward gear assembly locked and the input torus
Torus
In geometry, a torus is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle...
now ran at engine speed. This had the desirable effect of "tightening" the coupling
Fluid coupling
A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch...
and reducing slippage, but unfortunately also produced a somewhat abrupt shift. It wasn't at all uncommon for the vehicle to lurch forward during the 1-2 shift, especially when the throttle was wide open.
Upon shifting to third, the forward gear assembly went back into reduction and the rear gear assembly locked. Due to the manner in which the rear gear assembly was arranged, the coupling went from handling 100 percent of the engine torque to about 40 percent, with the balance being handled solely by the gear train. This greatly reduced slippage, which fact was audible by the substantial reduction that occurred in engine RPM
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
when the shift occurred.
The shift from third to fourth gear locked the forward gear assembly, producing 1.00:1 transmission. The fluid coupling now only handled about 25 percent of the engine torque, reducing slippage to a negligible amount. The result was a remarkably efficient level of power transfer at highway speeds, something that torque converter equipped automatics could not achieve without the benefit of a converter clutch.
Many Hydramatics did not execute the 2-3 shift very well, as the shift involved the simultaneous operation of two bands and two clutches. Accurate coordination of these components was difficult to achieve, even in new transmissions. As the transmission's seals and other elastomers aged, the hydraulic control characteristics changed and the 2-3 shift would either cause a momentary flare (sudden increase in engine speed) or tie-up (a short period where the transmission is in two gears simultaneously), the latter often contributing to failure of the front band.
From 1939-1950, the reverse anchor was used to lock the reverse unit ring gear from turning by engaging external teeth machined into that ring gear. From 1951 on, a cone clutch did the same thing when oil pressure was up, and a spring-loaded parking pawl was allowed to lock the same ring gear in the absence of oil pressure. This worked better as the anchor would not grind on the external teeth if that ring gear were turning (that is, unless the engine stalled as reverse was engaged). Reverse was obtained by applying torque from the front unit (band on, in reduction) through the fluid coupling to the rear unit sun gear. The planet carrier of this gearset was splined to the planet carrier of the reverse unit. The rear unit ring gear hub had a small gear machined on its end which served as the reverse unit sun gear. Because the rear unit band was not applied for reverse, the rear unit and reverse unit compounded causing the combined planet carriers to rotate opposite to the input torque and at a further reduced speed. The output shaft was machined onto the rear unit and reverse unit planet carriers.
Shutting off the engine caused the transmission oil pressure to rapidly dissipate. If the selector lever was in reverse or moved to reverse after the engine stopped, two mechanical parts combined to provide a parking brake. The reverse unit ring gear was held stationary by the reverse anchor. The drive shaft could still turn causing the reverse unit sun gear and attached rear unit ring gear to rotate at a very high speed, were it not for the fact that the rear unit ring gear band was now applied by a heavy spring. Usually, bands are applied by a servo
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
and released by spring pressure, but in this case, the band was held off by the servo and applied by spring pressure (actually, when the engine was running, the band was applied by a combination of spring pressure assisted by oil pressure). With the engine off, this brake band acting on the rear unit ring gear had a tremendous mechanical advantage. Since the rear unit ring gear with its attached reverse unit sun gear and the reverse unit ring gear were both locked to the transmission case, the planet carriers and driveshaft could not turn. As such, it provided an effective driveshaft mounted parking brake to be used alone or supplementing the hand brake.
Interesting facts
- A massive fire that destroyed GM's Hydramatic plant in Livonia, MichiganLivonia, MichiganLivonia is a city in the northwest part of Wayne County in the U.S. state of Michigan. Livonia is a very large suburb with an array of traditional neighborhoods connected to the metropolitan area by freeways. The population was 96,942 at the 2010 census, making it Michigan's 9th largest...
on August 12, 1953 left the corporation and the three divisions that used this transmission scrambling for other sources of automatic transmissions to complete that year's model year production. As a result, OldsmobileOldsmobileOldsmobile was a brand of American automobile produced for most of its existence by General Motors. It was founded by Ransom E. Olds in 1897. In its 107-year history, it produced 35.2 million cars, including at least 14 million built at its Lansing, Michigan factory...
s and CadillacCadillacCadillac is an American luxury vehicle marque owned by General Motors . Cadillac vehicles are sold in over 50 countries and territories, but mostly in North America. Cadillac is currently the second oldest American automobile manufacturer behind fellow GM marque Buick and is among the oldest...
s during the downtime were assembled with Buick's DynaflowDynaflowDynaflow 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...
transmission, while PontiacPontiacPontiac was an automobile brand that was established in 1926 as a companion make for General Motors' Oakland. Quickly overtaking its parent in popularity, it supplanted the Oakland brand entirely by 1933 and, for most of its life, became a companion make for Chevrolet. Pontiac was sold in the...
s used ChevroletChevroletChevrolet , also known as Chevy , is a brand of vehicle produced by General Motors Company . Founded by Louis Chevrolet and ousted GM founder William C. Durant on November 3, 1911, General Motors acquired Chevrolet in 1918...
's PowerglidePowerglideThe Powerglide is a two-speed automatic transmission designed by General Motors. It was available primarily on Chevrolet from January, 1950 through 1973, although some Pontiac models also used this automatic transmission, extensively on models produced for the Canadian market with Chevrolet...
, both two-speed torque-converter units. Non-GM makes that bought Hydramatics from the corporation, including Ford Motor Co.'s Lincoln division and independent automakers Hudson, Kaiser and Nash, ended up looking for other sources of automatic transmissions as well, with Lincoln using the Borg Warner designed Ford-O-Matic transmission, while other automakers also switched to automatics from Borg-Warner during the downtime. - About nine weeks after the Livonia fire, GM opened up a new source for Hydramatic production at Willow RunWillow Run TransmissionWillow Run Transmission is a General Motors factory in Ypsilanti Township, Michigan. Opened in 1953, it produced Hydra-Matic automatic transmissions for use by General Motors and others...
, Michigan. By the time the 1954 models debuted in late 1953, Hydramatic production had returned to normal levels and all '54 model Cadillacs, Oldsmobiles and Pontiacs with automatic transmissions were once again equipped with Hydramatics. - The first-generation Hydramatic (not the Jetaway version that succeeded it in 1956) did not have a separate park position as found in modern automatic transmissions. The driver had to shut off the engine and then place the transmission in reverse in order to lock the driveline to prevent the car from moving. Also, the original Hydramatic required periodic band adjustments as a routine maintenance item that later versions did not.
- The first version of the Hydramatic used a mechanical pawlPawlPawl may refer to:* A common component of a ratchet* A part of the adjustable height locking mechanism of an extension ladder* Pawl , a former racing car constructor...
to lock the planet carrier of the reverse gearset when the driver wished to back the vehicle. This arrangement did not work well in practice and was replaced with a cone clutchCone clutchA cone clutch serves the same purpose as a disk or plate clutch. However, instead of mating two spinning disks, the cone clutch uses two conical surfaces to transmit torque by friction....
. - The all cast-iron Hydramatic was the heaviest automatic transmission ever produced for automobiles.
- Both the "Jetaway" and "Roto" Hydramatic transmissions used what now seems like an unusual gear selection sequence of N-D-S-L-R, rather than the more common P-R-N-D-S-L sequence used on virtually all three-speed automatics since the 1950s (including the Turbo-Hydramatic, which replaced the Hydramatic/Jetaway/Roto transmissions). However, this was really not unusual at all. Virtually all early U.S. automatic transmissions used some variation of the N-D-L-R or P-N-D-L-R gear selector sequence, except those from Ford Motor Co. The reason given for placing Low gear and Reverse adjacent to each other in early automatics, according to contemporary owners' manuals, was to facilitate "rocking" the car back and forth to get "unstuck" in mud or snow. Indeed, it was Ford's transmissions that were the exception prior to the federal government's mandating the P-R-N-D-L sequence in 1964.
- Joe Hill LouisJoe Hill LouisJoe Hill Louis , born Lester Hill, was an American singer, guitarist, harmonica player and one-man band...
recorded a song named "Hydramatic Woman". - The Hydramatic Division of GM produced contracts of M16a1 rifles for the US Military during the Vietnam War.