Patent GB-692170-A (GB)
Title: Improvement relating to change-speed gearing
IPC: F16H63/02
Filed: 1951-05-09
Abstract: 692,170. Controlling variable-speed gearing. DAIMLER-BENZ AKT.-GES. May 9, 1951 [March 11, 1949], No. 10916/51. Class 80 (ii). In an automatic change-speed gear particularly for vehicles, a delay device is incorporated to prevent a change, being effected immediately upon the incidence of conditions necessary to effect such change. As shown a gear changing rod 18 is adapted to be moved to the left or the right for engaging a direct or overdrive respectively by means of solenoids 29, 30 acting on a core 28 and is controlled by a centrifugal governor 7. This governor is driven by the engagement of a friction wheel 3 on the governor shaft 4 with a friction disc 2 on a vehicle driving shaft 1. The wheel 3 can also be moved axially on the shaft 4, to vary the radius of contact with disc 2, by a linkage connected to the accelerator pedal 5 of the vehicle. The governor sleeve 9 is thus made responsive to vehicle speed and the engine torque, as measured by the accelerator position, and carries an electrical contact 10 movable between two fixed contacts 11, 12 which control the change-down and changeup operations respectively. The delay device, which operates to prevent immediate change-up from direct to overdrive, comprises a dash-pot piston 50 operated by a solenoid 33 and controlling a switch 42 in the circuit of the solenoids 29, 30 of the gear changing rod 18. In operation with the parts in the positions shown, the shaft 1 rotating at an intermediate speed and the accelerator 5 in an idle or low load position, the direct drive is engaged, the governor contact 10 being in contact with fixed contact 11. The circuit 32, solenoid 33, switch 42, 44 and solenoid 29 to a current source 31 is thus made. The piston 50 is thus held in its left-hand position where it is held by a catch 63 and the gear change rod 18 is also held in its left-hand direct drive position. If the vehicle shaft speed is now increased to a value at which a change-up is desirable the governor contact 10 moves from contact 11 to contact 12 and a circuit 37, switch 38, 39, solenoid 40, switch 42, 44 and solenoid 29 is made so that no immediate movement of gear-change rod 18 is effected. However, the solenoid 33 is now de-energised and the catch 63 is released so that the piston 50 commences to move to the right by the spring 51 against the dashpot action. The time for the complete movement may be adjustable as desired by a valve 58 from 2 to 20 seconds and at the end of such movement the switch 42 moves from contact 44 to contact 46. This breaks the circuit through solenoid 29 and diverts it to solenoid 30 with the result that the rod 18 is moved to the right to effect the desired change-up to overdrive. If however before the piston 50 reaches its right-hand position to effect the change-up the road conditions change with a fall in the vehicle speed the governor contact 10 will move back from contact 12 to contact 11 which results in the solenoid 33 being again energised and the coil 40 de-energised. The piston 50 is thus returned to, and locked in, its left-hand position and as the coil 29 remains energised no change to overdrive is effected. For a normal downward; change from overdrive with the solenoid 30 energised and the piston 50 in the right hand position the governor contact 10 must move from contact 12 to contact 11 when the coils 33 and 29 are energised and coil 30 deenergised, the piston 50 being moved to the left without delay by reason of a one-way valve 56 and the change rod 18 also being moved to the left to change to direct drive. Friction present or provided in the governor linkage ensures that the change-down takes place at a lower speed than the change-up which is desirable to prevent constant changing. Under certain high speed and full load conditions it may be desirable to retain or engage a lower gear and this can be effected by moving the accelerator pedal beyond its full load position V and further reducing the speed of governor 7. Under idle or low load conditions it is desirable that the change to the lower gear is not left until the vehicle speed is too low and to guard against this another governor device 13, 14 on the vehicle shaft 1 is provided which controls contacts 16, 17 controlling a solenoid 67 for operating switch 38. At a predetermined low speed the switch 38 is moved to position 38<SP>1</SP> which has the effect of switching the circuit of contact 12 to contact 11 so that the lower gear is engaged irrespective of the accelerator position. The delay device circuit may be cut out if desired by operating a switch 72 to 72<SP>1</SP> so that the changes become immediate. Instead of the accelerator position controlling the speed changes this may be done by some other engine torque factor such as engine suction, or by a torque indicator on the engine or vehicle shaft and the action may be applied between the speed governor 7 and the change member 18 rather than at the drive of the governor 7. Only upward changes may be subjected to speed and torque control, the downward changes being controlled by the vehicle speed alone. Mechanical, hydraulic or pneumatic devices may be utilised instead of electrical. The automatic change may be applied to several or all of the gear changes.