Patent GB-892647-A (GB)
Title: Electrically controlled fluid actuated change-speed transmission
IPC: B60K20/00
Filed: 1959-05-04
Abstract: 892,647. Change-speed control. CATERPILLAR TRACTOR CO. May 4, 1959 [Feb. 27, 1959], No. 15135/59. Class 80 (2). [Also in Group XXIX] In a control for a motor vehicle change-speed gear providing five forward and one reverse ratios and an auxiliary two-speed gear ratio shift is selected by manual switches 18, 76 for the main and auxiliary gears, and established by pneumatic or hydraulic servos 29, 79 energized through solenoid valves 131 by electricallysensed synchronizing circuits, 14, 71. For upshift the main clutch 17 is released throughout the whole shift interval and a brake 143 applied to the gear input shaft to accelerate synchronism, whilst for downshift, in one embodiment (shown) the clutch remains engaged and the engine fuel control rack 149 is momentarily shut down to unload the transmission gears of drive-torque permitting them to neutralize; and in the other embodiment (Fig. 5, not shown) in which there is no synchronizing control of the auxiliary gear, there is no control of fuel, but the main clutch is released for neutralizing and is re-engaged for synchronizing prior to establishment of the new ratio. Synchronism is sensed by speed-responsive alternators 56, 57, 96 driven by the input and output shafts of the main and auxiliary gears. Electrical circuit.-The selector switch 18 comprises a handle which carries a spring- pressed contact 19 connected through a relay 36 and master switch 38 engaged by pressure in the fluid circuit to a battery 28. The contact 19 carries a roller 21 engaging a cam track 22, each trough of which corresponds to a gear ratio and has a contact 23 adjacent thereto which when engaged by the contact 19 energizes an appropriate solenoid valve of the shift servo. Adjacent to each crest are ganged contacts 24 connected through a capacitor 156 to a relay 154 for temporarily reducing engine fuel supply. The switch 18 also houses a micro-switch 27 closed by a one-way ratchet 26 on upshift to energize the clutch solenoid valve 144 of the clutch servo 138. The synchronizing circuit 14 for the main change-speed gear comprises input and output driven tachometer generators 56, 57 which supply speed-responsive alternating currents to contacts 63, 64 on a sliding bar 66 connected to move with the switch 18. The contacts 63, 64 engage a resistor track 62 connected through resistor banks 59, 61 to rectifiers 68, 69, the resistance ratio of said banks being inversely proportional to the corresponding shaft speed ratio so that when the input and output shafts are rotating at the selected ratio the currents supplied to the rectifiers are equal. The rectifiers are connected to the inputs of a transistorised differential null balance device 41 which when the input currents are unbalanced draws current from the battery 28 through a relay 42 energizing the latter which completes the circuit to the micro-switch 27 and breaks the circuit to the relay 36, de-energizing the latter which breaks the circuit to the contact 19. When the input currents to the device 41 are balanced, i.e. at synchronism, the relay 42 is de-energized, breaking the circuit to the clutch operating micro-switch and remakes the circuit to the relay 36 which in turn makes the circuit to the contact 19 and therethrough to the solenoid valves of the servos to establish the selected ratio. The auxiliary gear selector comprises a double-pole double-throw switch 74 one movable contact of which is connected through a relay 72 to the battery 38 and is engageable with contacts 77, 78 connected to the solenoid valves of the auxiliary gear servo 79. Input and output generators 96, 56 supply current through a resistance network 97 and rectifiers 93, 94 to the inputs of a transistorized balance device 89 to operate a relay 84 which operates the relay 72, supplying current to the switch contact 74 when energized and to the clutch-operating solenoid when de-energized for both up and down shifts. For reverse a manual switch 30 is tripped to break through the circuit to the selector switch 18 and complete the circuit to the solenoid valve of the reverse gear shift servo, the clutch 17 being operated manually. In Fig. 5 (not shown), reverse is provided by an additional selector contact 23. Fluid control.-The gear operating servos 29, 79 and clutch operating servo 139 may be hydraulic or pneumatic. The pneumatic gear operating servo, Fig. 3, comprises a double cylinder 111, 112 each chamber having a piston 113, 114 the former of which is fixed at 117 whilst the latter is connected to the shift fork 104. With both solenoid valves 121, 122 de-energized, as shown, pressure air is supplied to the right of each chamber forcing the pistons left and conditioning the shift fork 104 to neutral. When the solenoid valve 121 is energized pressure air is supplied to the left of chamber 112 which moves right the piston 114 and shift fork 104 to establish the gear ratio, e.g. second. With the solenoid valve 121 de-energized and the solenoid valve 122 energized pressure air is supplied to the left of cylinder 111 which moves left the cylinder together with the piston 114 to establish e.g. third ratio. The hydraulic servo, Fig. 4, comprises a stepped cylinder 127, 129 having a floating piston 126 in the larger diameter part and a piston 124 fast with the shift fork 104 in the smaller diameter part. With both solenoid valves 131, 134 de-energized, as shown, pressure liquid is supplied to each end of the cylinder moving the piston 126 right until it abuts the smaller diameter part of the cylinder and the smaller piston left until it abuts the larger piston for neutral. Energization of the solenoid valve 131 supplies pressure liquid to the centre of the cylinder and exhaust the right-hand side to move right the piston 124 for second ratio. Energization of the solenoid valve 134 with the valve 131 de-energized exhaust the left-hand side of the chamber and both pistons move left for third ratio. The servo for the main clutch 17 comprises a cylinder 138, the piston 139 which is connected to the clutch-operating pedal 142. Energization of the solenoid valve 144 supplies pressure fluid to the chamber which moves the piston 139 right to disengage the clutch 17 and apply a brake 143 to the input shaft. The clutch is reengaged gradually by exhausting the chamber 138 through a bleed hole 148. A pressure-responsive switch 38 breaks the electric shift circuit when servo pressure is low. Specification 783,322 is referred to.