Patent GB-1472352-A (GB)
Title: Automatic transmission control
IPC: F16H61/02
Filed: 1975-04-30
Abstract: 1472352 Change speed control CATERPILLAR TRACTOR CO 30 April 1975 [2 Aug 1974] 18030/75 Heading F2D  An hydraulic control system, for ratioestablishing clutches and brakes in a torqueconverter-driven planetary transmission on a motor vehicle, comprises a manual selector valve 110 which determines the highest ratio (that giving the highest output speed) at which the transmission can operate automatically in response to automatic shift valves 520, 522 ... 530, upshifted by differing outputspeed responsive governor pressures 218, 220, 222, in opposition to different fixed downshift reference pressures 258, 260, 262, the shift valves inhibiting forced downshift, requested by changing the setting of the manual valve 110, until output speed falls to the normal automatic downshift speed for the ratio requested. Function summary.-Of the eight forward ratios and single reverse, the first two ratios, neutral and reverse are selected manually by the valve 110, whilst automatic shift between ratios two to eight occurs at fixed upshift and downshift speeds, the highest permitted ratio being in accordance with the setting of the manual valve 110, whilst downshift to such a manually selected limit ratio occurs only automatically at the fixed governed speed. Reduction of pressure due to clutch or brake filling during shift closes a priority valve 142 maintaining hold pressure on the shift valves and also blocks governor pressures 218, 222 at 400 to avoid shift transients. Depression of an additional pedal 410 prevents any automatic shift. Fluid system. General.-The manual selector valve 110 and automatic shift valves 520 ... 530 function to exhaust a selected one of a number of conduits 296 &c. leading from axially spaced positions along power shift cylinder 116, having a piston 118 with a land 154, subject on opposite sides to equal pressures supplied to spaces 150, 152 through a line 156 and restrictors 160, 161, whereby the exhausting of a selected conduit 296 &c. exhausts one side of the land 154 and causes the piston 118 to shift axially until it covers the exhausted conduit and restores pressure balance in the new setting. Movement of  the shift piston 118, through linkage not described, actuates a selector valve group, not described, supplying the ratio clutches and brakes to establish a selected shift. Automatic shift valves 520 ... 530 are arranged in a group of three pairs, upshift-biased by governor pressures 218 ... 222. Downshift bias is provided by three individual fixed reference pressures 258, 260, 262, derived from four regulator valves 132 ... 138; and by "hold" pressure supplied at full line pressure from line 304, to lines 166, 168 ... 176, through the manual valve 110 to inhibit upshift beyond a selected limiting ratio. Shift control pressures. Governor.-Three distinct ranges of governor pressure (Fig. 8, not shown) are provided by three centrifugal regulator valves of an output-driven governor 114, feeding respective lines 218, 220, 222, acting below the three shift valve pairs. Reference pressures.-The three fixed reference pressures 258, 260, 262, acting downwards on the tops of the shift valves 520 &c. are provided by a group of four adjustably fixed regulator valves 132 ... 138, which receive line pressure 250 at 125-450 p.s.i. and regulate to four lines as follows. The first regulator 138 regulates 96 p.s.i. to a line 278, 156 feeding the power shift cylinder 116, the governor 112 and the remaining three regulator valves 132 ... 136, which regulate 38, 44, and 80 p.s.i., respectively to lines 258, 260, 262, the first, 258, providing downshift reference pressure for the 2-3 shift valve 520; the second, 260, for the 4-5 and 6-7 shift valves 524, 528; and the third, 262, for the 3-4, 5-6 and 7-8 shift valves 522, 526 and 530.  Operation.-Initially in neutral, N, all the automatic shift valves 520 ... 530 are in their lower, downshifted, positions, and the power shift piston 118 is one step to the right of the R setting shown. All lines from the power shift cylinder 116 are blocked, those 296, 298, 300 at the manual valve 110, the remainder at the shift valves 520 &c. The 96 p.s.i. line 278, 156 from the regulator 138 feeds pressure through the restrictors 160, 161 to the chambers 150, 152 on each side of the piston land 154, maintaining balance, and pressure from the right space 152 passes through a line 280, shift valve 520, passage 282, shift valve 522, passage 284 and similarly through the remaining shift valves 524 ... 530 and passages 286, 288, 290 to a line 292, leading to, and now blocked at the manual valve 110. Reverse.-Shifting the manual valve 110 to R opens the line 296 to exhaust at 164, exhausting the left chamber 150 of the power shift cylinder 116, and causing the now unbalanced piston 118 to be moved by the prevailing pressure 152 one step to the left to the R position, shown, in which its land 154 blocks the exhausting line 296 and restores pressure balance. The piston movement mechanically operates the selector valve group (not described), which establishes reverse. Neutral, first and second are similarly established by the power shift piston 118 following the steps of the manual selector valve 110 as it selectively exhausts the lines 298, 300 and 292. In neutral, reverse and first, the 96 p.s.i. pressure in the line 292 passes through the manual valve space 302 to all the "hold" lines 166 ... 176 where it acts downwardly on all the shift valves 520 &c. through spool ports 652 and cavities 651 in the spools. In second the lines 292 and 280 are exhausted at 192 and full line pressure 304 communicates with the manual valve space 302 and is supplied therefrom to the hold lines 166 ... 176 of all the shift valves to maintain downshift. Automatic shift.-Movement of the manual selector valve 110 to any of the settings three to eight prepares for automatic shift up to the limit of the selected setting. Assuming setting 3 to have been selected, 2-3 upshift is as follows. The manual valve 110 exhausts the second ratio hold line 166 at 192 leaving only the first reference pressure (38 p.s.i.) at 258 to bias the 2-3 shift valve 520 downwards. When the first range governor pressure 218 predominates over this reference pressure the spool of the 2-3 valve 520 is moved upwards, blocking the line 280, and exhausting the line 310 through the passages 282, the remaining shift valves, the line 292 and end 192 of the manual valve 110, the land 190 now being one step to the right of line 292. The power shift piston 118, now unbalanced, moves one step to the right until it covers the exhausting line 310, whereupon the piston is stabilized in 3 setting establishing third ratio. During the piston movement the line 280 comes under pressure from the chamber 150, and this pressure passes through radial ports in the shift valve spool 594 into a spool cavity 306 above the slug 231 on which latter it reacts to apply additional upshift force to the valve spool, producing a snap action, as well as hysteresis for an ensuing downshift. In 3 setting of the manual valve 110 upshift beyond third ratio is not possible since all the remaining hold lines 168 ... 176 of the shift valves 520 remain pressurized with full line pressure 304 and cannot be upshifted. As the manual valve 110 is moved progressively to settings above 3, the respective hold lines 168 &c. are successively exhausted, permitting automatic upshift of the respective shift valves to the selected limit, as described above for the 2-3 shift. Automatic downshift within the permitted range is the reverse of the above upshift action. If however the manual valve 110 is moved to a lower ratio setting for a forced downshift, although hold pressure may be supplied to the lines 166 &c. such pressure will be ineffective to produce downshift, since, in the upshift position of the shift valves 520 &c. the hold pressure is blocked by the valve spool land 594, and hence downshift to the selected ratio can only occur by automatic action due to governor and hysteresis pressure bias falling below the downshift bias of reference pressure 258 &c. Once the downshift has occurred, hold pressure will become effective to prevent further upshift. Shift override.-To prevent any shift at any time the driver depresses a pedal 410, which, by compressed air, closes a valve 408, cutting off the 96 p.s.i. pressure 156 from the power shift cylinder 116 thereby preventing movement of the shift piston 118 and hence preventing any shift. To prevent governor pressure fluctuation during a shift from influencing a shift, the governor pressure lines 218, 220, 222 are blocked by a valve 400 which is normally maintained open by line pressure 402, but which closes when line pressure falls during shift due to the flow requirement of filling the on-going clutches and brakes. The same pressure reduction also closes the priority valve 142 to maintain pressure in the hold lines 166 ... 176. Shift speeds and governor pressure curves are given in Fig. 8, not shown. A diagrammatic circuit, Fig. 2, not shown, shows an hydrodynamic retarder with control valve and heat exchanger, whilst Fig. 1, not shown, shows the planetary gear. All these elements, as well as the governor are detailed in various U.S.A. Specifications which are identified in the Specification.