Patent GB-1344971-A (GB)
Title: Transmission controls
IPC: F16H59/46
Filed: 1972-09-14
Abstract: 1344971 Change-speed control GENERAL MOTORS CORP 14 Sept 1972 [18 Oct 1971] 42640/72 Heading F2D On a motor-vehicle, smooth shift between ratio-establishing torque transmitting means of variable capacity such as friction clutches or brakes, in a gear transmission driven through a fluid torque converter, e.g. as described in U.S.A. Specification 3,321,056, but without the one-way devices, is obtained by control means, shown as electronic, which senses the speed of the engine (Ne), converter turbine (Nt), and final output (No), derives therefrom the accleration (At) and torque (Tt) of the converter turbine; compares the desired speed ratio with the instantaneous ratio (Ri) prevailing during the slip period of a shift; derives therefrom the instantaneous acceleration error (Ae); and, as a function of the above variables, controls the torque-capacity of the ratio clutches to bring the instantaneous ratio smoothly to a value consistent with the desired ratio. Thus the equation for an upshift from ratio R 1  to ratio R 2  is as follows:- where It is the moment of inertia of the converter turbine. Similar equations cover powersustained and overrun downshift to ratio R 1 , exept that an additional term proportional to output speed No is introduced to reduce downshift time. The control takes effect by varying the energizing current applied to solenoid valves (42, 48) supplying fluid pressure to engage the ratio clutches, the magnitude of such pressure, and hence torque capacity, being a function of the energizing current (such valves are described in U.S.A. Specification 3,225,619), and the electronic circuit produces a current analogue for this purpose. The electronic circuit derives the pressure controlling current analogue by integrating the acceleration error Ae, (derived from the above equation) with respect to time. Turbine torque Tt is derived from the approximation Tt=Kc(Ne+Nt) (Ne-Nt), Kc being a constant of the torque converter. Signals representing the above equations are derived by feeding the Ne, Nt and No signals to a control circuit, Fig. 6, comprising summing, differential summing and multiplier circuits producing two output signals 68, 90, one RiTt/R 1 It selected by a switch 80 when moved to upshift position C, the other RiTt/ R 2 It-KNo by the switch 80 in its downshift position D. A differentiator 92 produces from Nt the turbine acceleration At, which is fed through a summer 82 receiving also the above selected signal 68 or 90 to provide on a line 94 the acceleration error signal Ae appropriate to upshift or downshift represented by the equations given above. The Ae error signal 94 is fed to an integrator 98 through a summer 96, receiving also, in the closed position of a switch K, a line pressure command signal, the integrator having two feed-back circuits, one selected by a switch C, providing a limit stop (by a Zener diode), the other, selected by a switch M, a simple resistor. Integrator output is fed to a biased amplifier to produce an output signal extending from zero to a positive maximum, and fed through a summer 106 and switch L to a current driver 46 for the second ratio clutch valve-solenoid, the summer also receiving a fixed voltage to compensate for valve-solenoid offset. The current driver 40 of the first ratio clutch valvesolenoid is supplied through a summer 120 receiving the line pressure command through a switch G, and, through a switch D, receives the integrator output through an inverter 110 and amplifier 112, biased to produce a signal varying from zero to positive values, even when integrator output is negative, which results in overlapped clutch engagement at low values of integrator output. A second amplifier 114 produces a step output for a summer 116 to compensate for valve-solenoid offset. The various switches C ... M in the above control circuit are controlled by outputs of a logic circuit, Fig. 7, not shown, controlled by a shift command circuit (which may be manual or automatic as desired in Specification 1,174,710), which produces zero and one logic inputs when first and second ratios respectively are requested. Also forming inputs to the logic circuit are the signals Nt and No, the former being also differentiated to provide the turbine acceleration At signal. The logic circuit consists of OR, AND and NOR gates, comparators and a time delay, which take effect for 1-2 upshift as follows. When operating in first ratio switches C, K, L are open; M, D, G closed; switch 80 is in D position. The circuit is then such that full pressure is applied to clutch 1, clutch 2 is completely released, and integrator output is zero. When a shift command switch (130) commands upshift, switches C, L close D opens and switch 80 moves to C position. The second ratio clutch engaging line 46 is enabled and the acceleration error Ae is computed in accordance with the upshift equation above. Switch M opens so that the limit stop put in circuit by the switch C prevents negative voltages at the integrator output. The initial large Ae causes increase in integrator voltage, thus increasing pressure in the second ratio clutch, which causes turbine deceleration, which opens the switch G cutting off line pressure command for the first ratio clutch line 40 for rapid pressure drop in that clutch. With increasing integrator voltage and hence second clutch pressure turbine deceleration decreases until the upshift equation, above, is satisfied. Continuing increase in integrator voltage reduces the instantaneous speed ratio Ri, which modifies the deceleration requirement as Ri approaches R 2 , just before which switch K is closed exerting line pressure command on the integrator causing it to apply full pressure to the second clutch, thereby completing the shift. Downshift operates the switches to follow the downshift equation above, except that, if on power downshift, the turbine fails to decelerate during controlled slip of the second ratio clutch, the control of that clutch will be de-activated a half second after Ri reaches the desired approach value to R 1 .