Patent GB-1400359-A (GB)
Title: Vehicle drive systems
IPC: B60K5/08
Filed: 1973-11-16
Abstract: 1400359 Change-speed control CATERPILLAR TRACTOR CO 16 Nov 1973 [4 Dec 1972] 53399/73 Heading F2D [Also in Division B7] In a motor vehicle, such as an earthmoving scraper, having a first engine 1 driving tractor front wheels 13 through a change-speed transmission 19, and a second, scraper-mounted engine 21, driving rear wheels 17 through a similar transmission 22, the ratio shift controls of the two transmissions being interconnected, the front 19 acting as a master generating signals for shifting the rear 22 as a slave, anti-stall means is provided for automatically downshifting the slave transmission 22 to a predetermined ratio range if the ground speed falls below a predetermined value at which the range shift signal generated by the master 19 indicates a ratio range higher than the said predetermined range. Such a condition would exist when slip occurs at the wheels 13 driven by the master, and would, in the absence of the anti-stall means, cause overload and possible stall of the rear engine 21.  The transmissions 19, 22 are planetary and each comprise an hydrodynamic torque-converter effective in manually selected reverse first and second ratios only, being by-passed for allmechanical ratio ranges three to eight, which are selected automatically by an output-speed, and load control 29 operative on the shift lever 31 of the master transmission 19, and on first and second linked arms 37, 42 of a switch 23 connected, through a multiple cable 26 and pin plugs 54, 56, to a control 53 for the slave transmission 22. Manual movement of the master shift lever 31 between positions R, N, 1, 2, causes the first switch arm 37, energized through a manual switch 46 in a right-hand setting, to move over contact studs 38a ... 38d energizing, through the cable 26 and leads 52a ... 52d, the shift control 53 to produce changes in the slave transmission 22 corresponding to those in the master 19, whilst, over the automatic ranges three to eight, the second switch arm 42 contacts studs 43e ... 43f, energizing lines 52e ... 52f controlling the slave transmission 22, energizing current in that case being delivered from the first switch arm 37 through connected studs 38e ... 38f and pin terminals PC on the multicable 26, the remove PC pin feeding the centre terminal of an anti-stall pressure switch 57, responding, on a diaphragm 67 to the delivery pressure of a pump 72 driven by the rear wheels 17 and thereby sensing vehicle speed. If vehicle speed is consistent with the automatic ranges established, pump pressure will raise the diaphragm 67, breaking a contact 66 closing 64, which, through a terminal 62 and lead 69, supplies the PC current to pin terminals PA which energize the second switch arm 42 to establish in the slave transmission 22 the same ratio ranges as those automatically selected in the master 19. If, due, e.g. to wheel slip, forward speed is below that which would otherwise obtain in the automatic ranges, the delivery pressure of the pump 72 falls, causing the pressure switch 72 to break contact 64 and close 66 which then, through the terminal 63 directly energizes the second range lead 52d of the slave transmission 22, downshifting the latter to fluid-driven second range. Snap action and hysteresis is provided for the pressure switch 57 by an adjustably spring- loaded regulator valve 74 with restrictors 93, 96 in the fluid path thereto. The manual switch 47 through which the first switch arm 37 receives its current has an alternative leftward setting energizing a contact 49, which neutralizes the slave transmission 22 when only the first engine 1 is required for propulsion. The controls may alternatively be electronic, with electrical speed sensing and Schmitt trigger snap action, or fluidic.