Patent GB-885480-A (GB)
Title: Improvements in hydrodynamic transmissions
IPC: F16D67/00
Filed: 1960-02-10
Abstract: 885,480. Change-speed control. GENERAL MOTORS CORPORATION. Feb. 10, 1960 [Feb. 26, 1959], No. 4660/60. Class 80 (2). [Also in Groups XXIX and XXXIV] A hydromechanical variable-speed transmission for a motor vehicle includes a fluid coupling 62 which may be operated to produce hydrodynamic braking augmenting that from a dualturbine torque converter 14. Transmission.-As shown this comprises driving and driven shafts 10, 12 with the dualturbine torque converter 14, the reactor vanes 16 of which may be adjusted by a servo-piston 22. A torque-multiplying planet gear unit 28 is provided between the turbines T 1 , T 2 . Forward drive and reverse planet gear units 40, 42 are rendered operative by fluid-pressure operated brakes 54, 82. The direct-drive fluid coupling is of the fill and dump type and comprises an impeller 64 and turbine 66 with a lock-up clutch 68. An overrun brake 58 is also provided. Oneway detents 24, 38, 52 are associated with the torque converter reactor S, and the reaction stun gears of the torque-multiplying and forward drive gear units 28, 40. Control system.-A pump 86 driven by the input shaft 10 supplies pressure fluid through a pressure-regulating valve 90 and supply line 88 to a manual selector valve 96 having park, neutral, drive, intermediate, drive brake, and reverse positions (PNDID B R). A primary throttle valve 112 is operated by the accelerator pedal 118 having an associated kick-down electric switch 326. A secondary throttle valve 154 modulates the fluid pressure in accordance with variations in the primary throttle pressure. A governor valve 208 is mounted in a rotatable valve body 94 and functions as a regulating valve to increase the pressure of fluid delivered to a supply line 216 with increasing speed of rotation. In addition a shift valve 190, detent valve 146 for forced downshift, discriminator valve 274, and valves 130, 172, 260 for operation the overrun brake 58, forward drive brake 54 and lock-up clutch 68 are provided. Valves associated with the fluid coupling 62 comprise a dump valve 290, exhaust rate valve 240 for controlling the rate of exhaust from the coupling according to whether it is operating as a clutch or brake, and a limit valve 226 protecting the system downstream against excessive pressure drops resulting from filling the coupling. Operation.-(a) In neutral all the clutches and brakes are disengaged, coupling 62 is empty and torque converter 14 is effective, but no drive can be transmitted to forward or reverse gear units 40, 42. (b) In the drive range brake 54 is engaged and drive is transmitted from input shaft 10, through torque converter 14 and turbine gear unit 28 to forward drive unit 40. At a selected speed fluid coupling 62 is filled, giving substantially direct drive, and some time after the establishment of this high-speed ratio the lock-up clutch 68 is engaged for true direct drive. Under these conditions the reactor vanes 16 may be moved to the high angle position for increased torque multiplication in converter 14 and for improved acceleration. (c) In the intermediate range conditions are as for low speed ratio in the drive range, except that overrun brake 58 is engaged. Hence during overrun there is overspeeding of the second turbine T 2 , but the engine resists overspeeding of the impeller I, so the fluid in the converter is churned and slows the second turbine, thus giving moderate hydrodynamic braking. (d) In the drive brake range, for use if greater braking is desired, the units are as in the intermediate range except that coupling 62 is full. Overrun brake 58 then holds both the coupling turbine 66 and the reaction sun gear of the forward drive unit 40, the coupling impeller being driven by the second turbine T 2  to churn the coupling fluid with resulting augmented hydrodynamic braking. Governor valve 208 operates to supply fluid at higher pressure as speed is increased, so that overrun brake 58 is engaged more firmly. (e) In the reverse range only brake 82 is engaged, the drive train then passing from input shaft 10, through torque converter 14 and gear unit 28 to reverse gear unit 42. Modifications,-According to a first modification, Fig. 5 (not shown), the coupling impeller 64 is connected directly to the input shaft 10, while the turbine 66 is connected to the reaction sun gear of the forward drive unit as in Fig. 2. In a second modification, Fig. 6 (not shown) the coupling impeller 64 is connected directly to the output shaft 12 and the turbine 66 as in Fig. 2 and in addition the reverse gear unit is modified.