Patent GB-1432948-A (GB)
Title: Control circuits
IPC: G02B27/28
Filed: 1972-07-14
Abstract: 1432948 Change speed control CAV Ltd 28 June 1973 [14 July 1972] 32979/72 Heading F2D In a fluid-coupling-driven automatic transmission on a motor vehicle wherein ratioestablishing brakes are engaged directly or hydraulically by respective solenoids such as 24, selectively energized by rendering conductive respective transistors such as TR6, under control of a vehicle speed sensor 18, a first means, Fig. 4, is provided for delaying the conduction of a selected transistor and a second means, Fig. 5, for adjusting engine fuel supply during the relay period, when establishment of the selected ratio would reduce engine speed for a given vehicle speed (i.e. for upshift). The delay period may be reduced with increase in speed, and the fuel reduction may be appropriate to the ratio selected. The basic shift circuit, Fig. 3, one of which is provided for each ratio solenoid 24, has a common stabilized positive line 31, negative line 30, and a line 7 fed through a rectifier by an output speed sensor 18, such as an A.C. generator, to become increasingly negative with speed increase. At speeds above a predetermined value, specific to each ratio circuit, and determined by adjustable potentiometers VR1, VR2, the negative speed signal 7 renders previously conducting NPN transistors TR2, TR1 non-conductive, TR3 conductive, TR4 non-conductive and a Darlington pair TR5, TR6 conductive, whereby the ratio soelnoid 24 is energized from an unstabilized positive line 32. When, with increase in speed, the solenoid of the next higher ratio is energized, its circuit, the same as Fig. 3, applies a signal by way of a diode D4 to a terminal 34 of off-going ratio circuit to turn of TR5, TR6, de-energizing the solenoid 24. The above named first means, for delay, Fig. 4, has terminals 1.. 4 connected to the same numbered terminals of Fig. 3. When the speed sensor 18 signals a shift, the transistor TR4, Fig. 3, is rendered non-conductive and the consequent positive potential at its collector passes through the line 3 to switch on a transistor TR9, Fig. 4, off TR10, and on TR11, producing a negative potential on the line 4, which holds off the Darlington pair TR5, TR6, Fig. 3, thus preventing energization of the ratio solenoid 24 and holding the transmission in neutral. At the same time a capacitor C3 begins to discharge through a resistor 22, and after a predetermined time delay, switches on TR10 and off TR11, permitting the Darlington pair TR5, TR6 to switch on and energize the ratio solenoid 24. A delay circuit such as Fig. 4 may be provided for each of the ratio circuits, Fig. 3, or alternatively a single common delay circuit is connected to the 3 terminal through diodes D12, the TR9 plate of the capacitor C3 being connected through a resistor R26 to the terminal 7 so that the delay time is reduced with speed increase. Further, the collector of TR11 is connected, not to the terminal 4, but to a point in a circuit 33, Fig. 3, including a transistor which must be on for solenoid energization, but is turned off during the delay period. The second above-named circuit, Fig. 5, for engine fuel reduction, has one section to the left of the chain lines connected at 1, 2, 5 to each individual solenoid circuit, Fig. 3, and a section to the right of the chain lines common to all the individual circuits. When, as a consequence of speed increase, TR3 in one of the shift circuits, Fig. 3, is rendered conductive, the negative signal then appearing at its collector passes through the line 5 to switch off a transistor TR12, Fig. 5, on TR13, off TR14, and on a Darlington pair TR15, TR16, which energizes a winding 16 actuating the engine fuel pump to reduce engine fuel supply. When, after a suitable delay period, a capacitor C4 discharges through a resistor R26, TR12 is switched on to cause de-energization of the winding 16 thus terminating engine fuel reduction. This circuit may be subject to initial delay by an additional delay circuit, such as Fig. 4, a common delay circuit being used for a fixed delay, or individual circuits for each ratio circuit to provide a delay in initiating engine speed reduction appropriate to the particular ratio controlled by the circuit. The fuel reducing circuit itself may be common to all the ratio circuits and be connected thereto by diodes such as D12, Fig. 4, or individual circuits may be used. The delay and fuel reducing circuits operate only on increasing vehicle speed, since the speed signal does not increase negatively with speed reduction.