Patent GB-940413-A (GB)
Title: Hydraulic control system for a transmission
IPC: F16H47/08
Filed: 1961-09-15
Abstract: 940,413. Change-speed control. GENERAL MOTORS CORPORATION. Sept. 15, 1961 [Sept. 20, 1960 (2)], No. 33152/61. Headings F2D, F2E and F2F. An hydraulically applied and released ratio establishing band brake 35 in a change-speed gear has a release chamber 361 permanently connected to one side of a timing piston 391, the opposite side of which communicates selectively with exhaust or a source of pressure to vary the delay when releasing the brake. Gearing.-The gearing provides neutral, three forward speed ranges and reverse, and comprises an hydraulic coupling 11 having an impeller 12 driven by an input shaft 10 and clutchable by an hydraulically engaged friction clutch 28 to a ring gear 18 of a front planet gear 15, a first turbine 13 fast with a sun-gear 24 of a rear planet gear 20, and a second turbine 14 fast with the planet carriers 16, 21 of the planet gears and with an output shaft 39. The front ring gear 18 is stationable by an hydraulically applied cone brake 33 for reverse and the front sun 19 is fast with the rear ring 23 and stationable by the band brake 35. Operation summary.-The gearing is controlled by an hydraulic system having a manual selector valve 70 with park P, neutral N, drive range D, intermediate range I, low range L and reverse R positions. In park and neutral the coupling 11 is filled and the clutch 28 and brakes 33, 35 disengaged. In the D position three speed ranges are provided. For first speed drive the coupling 11 is filled and brake 35 applied, so that initially turbine 13 drives through the rear reduction gear 20 with the turbine 14 initially stationary and acting as a reaction member. As the output shaft speeds up the turbine 14 speeds up and acts as a forwardly rotating reaction member, the torque multiplication through the coupling 11 diminishing but not dropping to zero. For second speed the coupling is emptied and clutch 28 and brake 35 are engaged so that the input shaft drives the output shaft at the reduction ratio of the front gear unit 15. For third speed the coupling is filled and the clutch 28 remains engaged and brake 35 is released. The ring and planet carriers of both the front gear unit 15 and the rear unit 20 are driven at substantially engine speed so that both gear units are locked up to give direct drive. In reverse the coupling is filled and the reverse brake 33 is applied. Servo pressure supply and regulation.-The capacity of a single input-driven pump 50 is varied in accordance with the position of a slide 51 biased towards an upper maximum supply position by a spring 52 assisted by the supply line pressure 400 supplied to a lower chamber of the pump through a passage 64 by a pressure regulator valve 55. With increasing delivery pressure (line pressure 400) valve 55 is moved downwardly in opposition to a spring 61, to exhaust the lower pump chamber and supply pressure through a passage 65 to the upper pump chamber, forcing the slide downwardly to reduce the pump output. A throttle variable pressure is provided in a passage 407 under the control of a throttle valve 90 responsive to the position of the accelerator pedal, the pressure in passage 407 acting on the end of a pressure drop valve 290 to produce a pressure in a passage 408 varying inversely with the throttle pressure (T-V 407 pressure), and the passage 408 pressure acts on differential lands 56, 57 of the pressure regulating valve 55 to bias the valve downwardly against the spring 61 towards its minimum pressure position so that the line pressure 400 is increased as the throttle is opened. Under certain operating conditions pressure is supplied through a passage 416 to bias the valve 55 upwardly to increase the line pressure 400. Operation. Park and neutral.-The manual valve 70 must be moved to its park or neutral positions before the engine starting circuit can be completed. In the park position a locking dog (not shown) engages teeth associated with the output shaft 39 to positively station it. With the accelerator pedal released the pressure drop valve 290 admits full line pressure 400 to the passage 408 to move valve 55 downwardly to maintain a line pressure 400 of 66 p.s.i. At full throttle a pressure of 95 p.s.i. is maintained. In park and neutral when the pump operates the coupling 11 is filled with liquid and the brakes 33, 35 and clutch 28 are disengaged. A coupling timing valve 200 is biased by a spring 217 to the position shown in which line pressure from passage 400 is admitted to a passage 409 and acts on the head of a valve 305 to block off the coupling exhaust port 310. Passage 400 supplies liquid to the coupling through a restriction 156 and passages 410, 411. Passage 409 also leads to one end of a valve 220 which at heavy throttle opening is depressed against spring bias to admit pressure from passage 400 to a coupling supply passage 412, 411 to fill the coupling rapidly. Drive.-Low gear: coupling filled, band brake 35 applied. In the D setting of valve 70 the coupling 11 remains filled and line pressure 400 passes through the valve to a passage 401 leading to a boost valve 180 which is moved to the right to apply line pressure 400 to a passage 416 to act on the valve 55 augmenting the spring bias and raising the line pressure 400 to a maximum of 164 p.s.i. The passage 401 is connected to a band brake 35 apply passage 413 through a restriction 131 to smooth brake application at light throttle openings. With increased throttle opening the throttle valve 95 by-passes the restriction 131 to apply the brake 35 rapidly. 1-2 upshift.-An output driven governor 135 is supplied by the passage 400 and provides G1 and G2 pressures in passages 228, 229. At some vehicle speed G1 pressure in passage 228 acts on a land 234 of a governor valve 231 and moves it and a shift valve 232 to the right to open a passage 418 to exhaust to relieve the pressure acting on the right-hand land 206 of the coupling timing valve 200. Line pressure 400 is admitted through passage 401 and the governor valve 231 to a passage 427 to engage the front gear unit clutch 28. The pressure in passage 427 acts on the left-hand land 201 of the coupling timing valve 200 and moves it to the right against spring 217, thus connecting passage 409 to exhaust which opens the dump valve 305 to empty the coupling. The pressure in passage 427 also acts on the right-hand land of the boost valve 180, assisting a spring 187 to move it to the left to connect the boost passage 416 to exhaust to reduce line pressure 400 to 95-60 p.s.i. according to throttle opening. Passage 401 is connected to the band apply passage 413 through the restriction 131, and the release passage 414 is connected to exhaust. This gives second gear, the coupling being empty and the clutch 28 and brake 35 being applied. 2-3 upshift.-As the vehicle accelerates in second gear, G1 pressure from passage 228 acting on a land 144 of a governor valve 141 and G2 pressure from passage 229 entering a port 164 acts on a land 160 of a shift valve 142 to cause upshift to third gear at some vehicle speed. Movement of valves 141, 142 to the right applies line pressure 400 to the land 206 of the coupling timing valve 200 to shift it to the left. Line pressure 400 is therefore admitted through valve 200 to the passage 409 to close the dump valve 305. The valve 141 by-passes the restriction 156 between passages 400 and 410, 411 to give rapid fill of the coupling. Pressure from the feed passage 411 passes through a passage 422, the 1-2 shift valve 232, a passage 423 and the coupling timing valve 200 to the band brake release line 414. The pressure in the chamber 361 of the servomotor 40 aided by a spring 357a releases the band brake 35 notwithstanding the band apply pressure in chamber 360. Thus third gear is obtained, the clutch 28 remaining engaged, the coupling 11 being full and brake 35 being released. Timing of 2-3 shift.-The release line 414 is connected to the right-hand side of the timing piston 391 to vary the timing of the release for different throttle openings. The left-hand side of the timing piston 391 is connected by a passage 421 selectively to pressure or to exhaust under the control of a low throttle exhaust valve 375 and a band release valve 365. The low throttle exhaust valve 375 is biased to the left by a spring 385 and to the right by T-V 407 pressure, and the band release valve 365 is biased to the right by a spring 374 and to the left by coupling feed passage 411 pressure and the pressure in a passage 425 acting on differential lands of the valve 365. The pressure in passage 425 is derived from a pressure varying with throttle opening by a compensator valve 326 and varies with the engine delivered torque. At light throttle openings and while the coupling is being filled the valves 365, 375 are in the positions to which they are biased by their springs, in which line pressure 400 passes through passage 418 and the low throttle exhaust valve 375 to the passage 421 to move the timing piston 391 to its right-hand position. During upshift to third the band release passage 414 is connected to pressure, but since pressure is also acting on the left-hand side of the piston 391, the piston does not move and the pressure in passage 414 rises rapidly to release the brake 35. When the shift occurs at medium throttle opening T-V 307 pressure moves the low throttle exhaust valve 375 to the right. The band release valve 365 remains in its right-hand position during filling of the coupling, and thus the passage 421 is connected to exhaust through valve 375, passage 419, valve 365, passage 420 and timing valve 200. Thus band release 414 pressure causes the piston 391 to move to the left, delaying pressure build up to delay release of the brake 35 until the coupling pressure 411 is sufficient to move the band release valve 365 to the left to connect passage 421 to pressure passage 418 to prevent further movement of the timing piston 391. At large throttle o