Patent GB-1179207-A (GB)
Title: Variable-Ratio Power Transmission Mechanisms.
IPC: B60K17/10
Filed: 1968-10-11
Abstract: 1,179,207. Hydro mechanical variable-speed gear. GENERAL MOTORS CORP. 11 Oct., 1968 [16 Oct., 1967], No. 48232/68. Heading F2D. A hydro-mechanical variable-speed gear for a heavy duty vehicle comprises an input shaft 10 fast with a sun gear 24 of a torque splitting planet train 16 having a ring gear 36 fast with the input shaft 39 of a swash-plate pump 18 in closed circuit with a swash-plate motor 20 to form an hydraulic power path and a planet carrier 28 connectable to a output shaft 14 through a first mechanical power path including a low-intermediate range clutch 34; a high range clutch 74 for locking up the planet train 16 and a torque combining planet train 22 having a ring gear 72 fast with the output shaft 14, a sun gear 68 fast with the output shaft 47 of the motor 20 and a planet carrier 66 connectable with the input shaft 12 through a second mechanical power path including an intermediate-high range clutch 60. An additional reduction planet train 21 has output carried planets 50 meshing a sun gear 48 fast with the output of the motor 20 and a ring gear 54 which may be held by a low range brake 56. The clutches and brake may be operated mechanically, electrically, pneumatically or hydraulically. The pump and motor swashplates are variable between maximum forward and reverse displacement positions. Operation.-In the low ratio range the clutch 34 and brake 56 are engaged and the pump 18 is initially at zero displacement whilst the motor 20 is set to maximum forward displacement. To start the pump swash-plate is moved to a reverse displacement position. Increased output speed is obtained, in low range, by increasing the pump to maximum reverse displacement and thereafter reducing the motor displacement to zero. When the motor displacement is zero the output shaft 14 is driven through the first mechanical power path alone and the planet carrier 66 and gears 62, 64 are rotated from the output shaft to synchronize the clutch 60 for upshift to intermediate range which is established by engagement of the clutch 60 and release of the brake 56. In the intermediate range the output speed is increased by reducing the pump displacement to zero and simultaneously increasing the motor displacement to maximum reverse whereupon the clutch 74 is synchronized for upshift to high range. The high range is established by engaging the clutch 74 and disengaging the clutch 34. Thereafter further increase in output speed is obtained by increasing the pump displacement in the forward direction whilst reducing the motor displacement to predetermined values which provide maximum hydraulic pressure in the circuit. For downshifts the reverse procedure is employed which synchronizes the clutch 34 and brake 56 prior to engagement. Modifications.-In Figs. 3 and 4 (not shown), two parallel transmissions similar to the above are driven from an input shaft through a bevel reverse gear and their output shafts drive wheels or tracks on opposite sides of the vehicle. The transmissions may be controlled identically or may be controlled differentially for steering. Reference has been directed by the Comptroller to Specification 1,113,709.