Patent GB-1249180-A (GB)
Title: Automatic transmission systems
IPC: G01P3/488
Filed: 1969-11-17
Abstract: 1,249,180. Change-speed gear. TOYOTA JIDOSHA KOGYO K.K., and NIPPONDENSO K.K. 17 Nov., 1969 [28 Feb., 1969], No. 56097/69. Heading F2D. A solenoid valve 270 or valves, controlling fluid-pressure engaged ratio-selecting clutches and brakes 20, 30, 43, 60 of a two- or threespeed and reverse automatic transmission on a motor vehicle, is or are energized by a voltage signal 312 proportional to output speed, supplied by a notched-wheel magnetic pick-up 70 feeding a digital-analogue (D-A) converter 310, Fig. 8, and by a stepped voltage signal 321 proportional to engine-throttle opening, derived from a throttle-operated switch 320, Fig. 12, controlling tappings on a resistor-bank 324<SP>1</SP>, the speed and throttle signals feeding a discriminating circuit 330, the output of which, amplified or not, energizes the solenoid 280 of the shift-valve 270, the discriminating circuit 330 having in parallel a feed-back circuit 340 which provides operational hysteresis by ensuring that the downshift speed point is lower than that of upshift. Two embodiments are described, firstly a two-speed gear with single solenoid shift valve 270, and secondly a three-speed gear, Fig. 14, not shown, with two solenoid shift-valves. In both cases there is a complete discriminating and feed-back circuit for each shift-valve. Gear arrangement.-The gear, Fig. 1, driven through a torque-converter or fluid coupling, comprises input clutches 20, 30 driving selectively inner bevel side wheels 51, 57 meshing planets having larger steps 54 meshing a larger output side wheel 55. In all forward ratios the front clutch 20 drives the rear side wheel 51. First and reverse are by braking the planet carrier at 43, reverse using only the rear clutch 30. An intermediate ratio, where provided is by braking at 60 the front side-wheel 57, and direct drive high is by engaging both clutches 20, 30 together. Fluid circuit.-In the two-speed circuit, Fig. 2 an input-driven pump 17 supplies a manual shift-valve 261 having PRNDL settings, L providing a permanent first speed. In D setting the manual valve pressurizes a line 222 feeding the front clutch 20 (engaged in both forward speeds) and an automatic shift valve 270 which, in its spring-loaded rightward downshifted position (shown) feeds a line 224, 226 applying the first-speed brake 43, whilst in its upshifted leftward position, to which it is moved by energizing a solenoid 280, it pressurizes a line 223, 225 engaging the rear clutch 30 for directdrive, and exhausts the brake line 224. In both reverse and manual low, the brake 43 is applied through a line 227, in low together with the front clutch 20, and in reverse with the rear clutch 30. The three-speed gear, Fig. 14, not shown, has the additional brake 60 actuated by apply and release pressure-chambers for the intermediate ratio, and an additional solenoid shift-valve. Electric circuit.-Speed responsive voltage 321 is derived from a polarized stationary pickup 71 adjacent a notched wheel 72 rotating with the transmission output shaft, and feeding speed-responsive frequency to the D-A converter 310 (Figs. 10, 11, not shown), which comprises an amplifier, amplitude limiter providing wave-shaping, a frequency detector, rectifying and amplifier circuit. Throttle-responsive voltage is derived from a battery-fed resistor bank 324<SP>1</SP>, Fig. 12, having tappings which are opened successively as a contact arm 323 is moved anticlockwise by opening movement of the engine throttle. Voltage output is at 321 and a single resistor 330<SP>1</SP> remains in circuit at full throttle. Shift circuit.-The speed and throttle voltages 312, 321 feed the discriminating circuit 330, Fig. 8, which comprises a comparator 335, Fig. 13, receiving the speed and throttle voltages through potentiometers 337, 339 and leads 333, 332 respectively, and comprising a differential amplifier with Zener diode or a Schmidt circuit. A voltage signal is delivered to the output 331 when speed voltage predominates over throttle voltage to initiate upshift. The feedback circuit 340, which provides the operational hysteresis, comprises two transistors 341, 344 and a supply-voltage Vc. With zero output from the comparator 335, i.e. during low ratio, the transistor 344 is non-conducting and switches on the transistor 341 to ground the terminal 334. On upshift, the voltage signal at the comparator output 331 switches on the transistor 344, which switches 341, thus in effect increasing the speed-voltage input 335a to the comparator, thus reducing the downshift speed points.