Patent GB-1176851-A (GB)
Title: Improvements relating to Control Systems for Multi-Ratio Gearboxes.
IPC: F16H61/02
Filed: 1967-03-02
Abstract: 1,176,851. Change-speed control. ROBERT BOSCH G.m.b.H. 2 March, 1967 [3 March, 1966], No. 9848/67. Heading F2D. A change-speed control mechanism for a vehicle provides for fully automatic shift in accordance with vehicle speed and accelerator position, and for manual shifts with automatic upshifts if the engine speed exceeds a predetermined value, and with downshift inhibition if such downshift would cause the engine speed to exceed the predetermined value, provision being made for disabling the downshift inhibition for use in emergencies such as brake failure. A gear lever has positions R, N, A, IV-I corresponding to reverse, neutral, automatic and fourth to first ratios, the gear being shifted by an electric motor 11 driven in one direction for upshifts on the actuation of a switch 24 controlled by a relay 26, and driven the opposite direction for downshifts on actuation of a switch 25 controlled by a relay 27. The relays are controlled by transistor trigger switches 12, 13. The motor 11 is driven in its upshift direction when an input transistor 29 of the switch 12 is blocked, so that a transistor 28 becomes conductive and an output transistor 36 also becomes conductive to energize the relay 26. Downshifts occur when an input transistor 35 of the switch 13 becomes conductive, thus blocking a transistor 34, and making transistors 32, 37 conductive to energize the relay 27. The bases and collectors of the transistors 36, 37 are coupled by resistors 38, 39 so that only one of these transistors can be energized at a time. The arrangement is such that transistor 29 is still conductive when transistor 35 becomes blocked so that an appropriate ratio remains engaged. The transistor switches 12, 13 have a control voltage from three sources applied to them, namely a first voltage derived from a D.C. source 67 and applied across a voltage divider 61-66 from which the first control voltage is tapped under the control of the gearshift lever 15 and applied to a diode 59 ; a second voltage derived from a battery 56 applied across a voltage divider 46-51 and tapped therefrom by a switch 14 in accordance with the ratio actually engaged; and a third voltage from an A.C. generator 73 rectified by a diode 74 and applied across a voltage divider formed by a potentiometer 77 and resistor 76. The sliding contact of the potentiometer 77 is actuated by the accelerator pedal 18 so that depression of the accelerator shifts the contact to the right to decrease the voltage applied to a diode 72. Diodes 59, 72 are connected to one side 43, 45 of voltage dividers 43, 42 and 44, 45 the other sides of which are connected to the switch 14. The voltage dividers 42, 43 and 44, 45 apply the control signals to the bases of the input transistors 27, 35 of the trigger switches. The switch 14 may be driven by the motor 11, alternatively it may be replaced by six limit switches actuated by the gear-box control linkage. In the position A of the gear shift lever fully automatic shifts occur in accordance with the output speed and accelerator position, in all other positions of the gear lever 15 a switch 69 opens to disable the accelerator position control. However in positions I-IV of the lever 15 automatic upshifts from the manually established ratio occur and downshifts to the manually selected ratio are inhibited to prevent over-speeding of the engine as determined by the output speed responsive voltage applied to diode 72 opposed by the gear engaged voltage controlled by the switch 14. To permit downshift despite overspeeding of the engine in the event of brake failure a switch 79 can be opened manually to remove the output speed responsive voltage.