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Although not strictly a part of classic torque converter design, many automotive converters include a lock-up clutch to improve cruising power transmission efficiency and reduce heat. The application of the clutch locks the turbine to the impeller, causing all power transmission to be mechanical, thus eliminating losses associated with fluid drive.
Frequent fluid changes, especially when used for towing, are the single best method to prevent shudder. A shudder occurs because the torque converter never fully enters "lock-up" and ends up bouncing in and out of lock-up to slip. This causes the engine to flare up and then down again as the clutch cannot hold back the power of the engine.
Many TCUs now have an input from the vehicle's traction control system. If the TCS detects unfavourable road conditions, a signal is sent to the TCU. The TCU can modify shift programmes by upshifting early, eliminating the torque converter lock-up clutch application, and also eliminating the first gear totally and pulling off in 2nd. [3]
By historical context of comparison, the '50 Packard Ultramatic which was a torque converter applied two speed lock-up design with high and low range for four forward speeds and the '50 Studebaker/Detroit Gear featured a lock-up torque converter with three forward speeds. The lock-up feature of Packard's Ultramatic and Studebaker's DG 250 is ...
For the 1981 model year, a lock-up torque converter was introduced which coincided with the new EMC control of most GM cars; this version is the THM350-C, which was phased out in 1984 in GM passenger cars for the 700R4. Chevrolet/GMC trucks and vans used the THM350-C until 1986. The lock-up torque converter was unpopular with transmission builders.
The 5G-Tronic (model W5A 330 and W5A 580 · type 722.6) is an electronically shifted 5-speed overdrive automatic transmission with torque converter lock-up (typically in gears 3, 4 and 5) and 2-speed for reverse.
The design of most manual transmissions for cars is that gear ratios are selected by locking selected gear pairs to the output shaft inside the transmission. This is a fundamental difference compared with a typical hydraulic automatic transmission, which uses an epicyclic (planetary) design, and a hydraulic torque converter.
The first Ultramatic Drive was a hydraulic torque converter automatic transmission with a two-speed plus reverse epicyclic geartrain, with torque converter lockup, called "Direct Drive" by Packard. The unit was fully hydraulically controlled with a "valve body," like most early automatic transmissions before the advent of electronic control.