Patent GB-1525302-A (GB)
Title: Automatic gearboxes
IPC: F16H61/02
Filed: 1976-01-23
Abstract: 1525302 Change-speed control AUTOMOTIVE PRODUCTS Ltd 23 Jan 1976 [31 Jan 1975 (2)] 4376/75 and 4377/75 Heading F2D In an electronic control for solenoid valves of ratio-establishing clutches and brakes of an automatic planetary change speed gear on a motor vehicle, responding to signals 110, 150 representing respectively output speed and engine-throttle opening, together with a manual control for forward, neutral, reverse and ratiohold, shifts between forward and reverse are prevented above a predetermined vehicle speed and a switching circuit is arranged, when more than two of the valve-solenoids are energized to disconnect the power from all the solenoids so that none is energized, and this circuit includes a delay circuit to inhibit its operation during gear shift. Additional circuits provide a delay for the throttle signal 150 to limit its rate of change, thereby avoiding incorrect shift sequencing due to otherwise rapid change in signal level. Fourth or second ratio is temporarily engaged when a forward ratio or reverse respectively is selected from standstill. Fluid pressure in the servo system is increased at large throttle openings below a predetermined speed. Manual hold settings hold individual ratios subject to automatic upshift at speeds higher than normal full throttle automatic shift speeds. Gear type.-The planetary gear, not described, is of the kind having a forward clutch engaged in all forward ratios; a one-way sprag brake for automatic first; friction brakes for second and third ratios and reverse; and a direct-reverse clutch. Circuit.-Each of the three ratio shifts has a separate signal generating circuit 120, 121, 122 respectively, in the form of a transistor pump circuit comprising a resistor 130, 131, 132, and diode 134, 135, 136 which produces a speed analogue voltage signal, derived from an inductive pick up 110, wave shaped by transistors 113, 114, amplified and limited by transistors 116, 117, and applied at 157, 158, 159 to a voltage divider 138, 139, 140, the other end of which receives a throttle signal 150 from an accelerator-operated potentiometer 151, subject, for the purpose above referred to, to a delay circuit comprising a capacitor 156, 160, 168 and resistor 153, 154, 155. Speed-throttle signals calibrated to the three ratio shifts thus appearing at 157, 158, 159 activate amplifier trigger circuits 170, 171, 172 all set to change state at the same value, which is different for upshift and downshift to provide hysteresis. Variation of supply voltage in the triggers is cancelled by similar variation in the signal generators. The trigger circuits 170 . . . 172 control output stages 212, 219, 231 and 243 energizing respectively the valve solenoids of the brakes for reverse (216), second (221) and third (252) ratios and the direct-reverse clutch (253). During a shift between forward ratios energization of an on-going solenoid is instantaneous, whilst de-energization of the off-going solenoid is subject to delay by capacitor delay circuits 202, 237, connected to a summing junction 218 of the second output stage 219; 227, 241 connected to a summing junction 230 of the third stage 231, and 240, similarly connected to the fourth output stage 243. Thus, on a 2-3 shift, the trigger stage 171 instantaneously energizes the third ratio solenoid at 252, whilst discharge of the capacitor in the delay circuit 237 delays fall of potential at the junction 218 and hence de-energization of the second ratio solenoid 221. The simultaneous energization of more than one of the valve solenoids (excluding that of the forward clutch) is prevented as follows. The earth return for all the solenoids is completed through a line 268 earthed by a transistor 267 rendered conductive by transistors 258, 264, 265. The base of the transistor 258 is connected through a diode 261 to a terminal 262 which is connected to the feed line of the forward clutch solenoid which is at potential +V volts with the forward clutch engaged and at zero volts with it disengaged (as in reverse). The base of 258 receives potential from a line 254 fed through resistors 251 ... 253 by all the valve solenoids (excluding that of the forward clutch). When only one such solenoid is energized the line 254 supplies + V volts to the base of the transistor 258 which is rendered conductive, along with 264, 265, 267 which completes the earth circuit for the solenoid return line 268. If more than one of the solenoids is enegized. the base potential supplied to the transistor 258 by the line 254 rises to a value insufficient to maintain conductivity, thereby breaking the earth circuit and de-energizing all the solenoids, which remain so until power is cut off and subsequently re-connected. To avoid such cut-off during a normal shift (which is torque overlapped), the transistor 258 is subject to a delay circuit 256, 257. In reverse, the terminal 262 is at zero potential and this circuit is therefore inoperative to effect de-energization. Manual control.-This provides PRND 321 and comprises a switch with five wafers 281 . . . 285. PRN of the wafer 281 connects to the speed circuit transistor to inhibit the speed signal. The 3, 2, 1 settings render conductive transistors 288, 289, 290, which apply to the respective voltage dividers 140, 139, 138 of the speed-throttle signal generators full line voltage equivalent to a full-throttle signal and reduce the speed signal. Diodes 292, 293 isolate the 2 and 1 lines and the effect is that, in 3 setting, 1-2 and 2-3 shifts occur at normal automatic speeds, but 3-4 occurs only at speeds above the full throttle automatic speed. In 2 setting 2-3 and 3-4 are both at higher than full throttle speeds, whilst in 1 setting all the shift speeds are raised to that level. In switch wafer 282, the PN D32 settings connect to the input of the reverse brake output circuit 212 to prevent its energization in these settings. In wafers 283 and 284, the movable switch arms F and R connect to two inputs of a logic circuit 320, comprising NAND gates arranged as a flip-flop 321 and a latching and inverting circuit 322. A third input is derived from the speed circuit transistor 116 through amplifier and pumping transistors 302, 307 and switching transistors which produce logic "0" or "1" at the input to the logic circuit 320 depending on whether vehicle speed is below or above a predetermined value (2 to 3 m.p.h.). The output of the logic circuit is fed through a transistor output circuit 328 and delay circuits 345, 350 respectively to the solenoids of the forward clutch and direct -reverse clutch, the arrangement being such that, above the predetermined speed, a manual shift from a forward ratio to reverse, or vice versa, does not change the logic output and the existing direction of travel remains unchanged.  The delay circuits 345, 350 ensure upon shift from standstill to a forward ratio or reverse, the trigger circuit 172 of the direct-reverse clutch, or that 170 of the second ratio brake respectively, is activated to cause temporary engagement of direct drive, or second ratio respectively, to prevent lurch. After a capacitor-determined delay the trigger circuit is de-activated and normal forward or reverse established. An output circuit 365 . . . 369 energizes a pressure-modulating solenoid valve to increase system pressure when the throttle signal is low, i.e. at large throttle openings, unless the vehicle speed rises above a predetermined value. The five wafer manual switch may be replaced by an equivalent semiconductor circuit.