Patent GB-1204837-A (GB)
Title: Speed control for automotive vehicles
IPC: G05D13/62
Filed: 1969-02-07
Abstract: 1,204,837. Automatic speed control. RCA CORPORATION. Feb.7, 1969 [Feb.14, 1968], No.6682/69. Heading G3R. A speed control system for a vehicle has means for setting into a capacitor 36 a voltage representing a desired speed; means 54 for setting a voltage representing a minimum speed below which speed control is to be inoperative; means 96 producing a voltage which is a measure of actual vehicle speed; two comparators 64, 44 which respectively compare the actual speed with the desired speed and with the minimum speed; means responsive to the output of the first comparator 64 to operate the throttle of the vehicle so as to maintain the actual speed equal to the desired speed; and means responsive to the second comparator 44 to disable the throttle operating means if the actual speed is below the minimum speed. The throttle is controlled by a bellows 152; the throttle is opened when bellows is drawn in by a vacuum. The bellows are connected either to a vent 168 or a vacuum 148, at the inlet manifold of the engine, by a valve 162 operated by a solenoid 92 which is energized through a transistor 94 when all inputs of a NAND gate 128 are high. A tachometer generator 98 with rectifier 106 provides a speed signal across resistor 114 which comprises a D.C. component with ripple. A three position push button 14 carried on the steering column provides the means for charging capacitor 36. In its first position shown button 14 connects a 12V supply 10 through resistors 22, 24, 25 to earth 26; about 6V appears across 24 and 25 and a 6V Zener diode 28 is not conducting; input 1 to a NAND gate 32 is low and a high input is applied to input 4 of the NAND gate 128. Potentiometer 54 sets the minimum speed; while the D.C. speed signal is below this value differential amplifier 44 gives a high output which sets a bi-stable 124 to its first state in which it applies a low input 3 to NAND gate 128. When the actual speed rises above the minimum the amplifier 44 output changes giving a high input 2 to NAND gates 32, 128. With capacitor 36 initially discharged zero input is applied to I of differential amplifier 64; as the speed signal appears at input NI the amplifier 64 gives a high output and an inverter 26 applies a low input 1 to NAND gate 128 and the output of inverter 140 is high. If push button 14 is pressed to its second position Zener diode 28 is connected by low resistance 34 to 12V supply and thus breaks down giving a high input 1 to NAND gate 32; provided the speed is above the set minimum (input 2 to gate 32 is high) the output of the gate goes low and that of inverter 138, high. The capacitor 36 can now charge through resistor 57 and diode 58 up to a value corresponding to the actual speed at that time, when differential amplifier 64 changes rendering the output of inverter 140 high, cutting off diode 58. The voltage on the capacitor remains set at this value until push button 14 is again actuated, discharging leakage being balanced by charging leakage through field effect transistor 55. The voltage can be reduced by depressing button 14 to its fullest extent when no voltage is applied to resistors 24, 25 and inverter 137 applies high input 3 to a NAND gate 135 causing its output to go low and discharge capacitor 36 through resistor 144 down to the new value corresponding to actual speed. With the desired speed set into capacitor 36 the first excursion of actual speed above this causes the output of inverter 126 to go low setting bistable 124 to its other state and apply high input 3 to NAND gate 128. When actual speed subsequently, falls below desired speed input 1 of NAND gate 128 goes high and valve 162 is changed over causing bellows 154 to adjust the throttle setting. The valve then cycles back and forth maintaining constant speed. Because the ripple on the speed signal is applied to amplifier 64 the valve cycles at the tachometer frequency so that solenoid 82 is energized for short periods and does not overheat. If brakes are now applied a contact 90 opens to disconnect solenoid 92 and a contact 76 closes giving a low output from inverter 82 to reset the bistable 124 to its first state and shutting down the automatic control. After the brakes are released automatic control can be restored simply by bringing the speed above the value set on capacitor 36 when bistable 124 will again be set to its second state. Alternatively provided that the speed is above the set minimum it can be restored by operating a switch 66 which directly resets the bistable 124. If, with the bistable 124 in its first state after a braking action, the push button 14 is depressed only to its second position the capacitor is nevertheless discharged to the new set value by way of NAND gate 134.