Patent GB-1091558-A (GB)
Title: Controls for power drive system
IPC: B61C17/12
Filed: 1966-06-15
Abstract: 1,091,558. Change-speed and clutch control. TWIN DISC CLUTCH CO. June 15, 1966 [July 19, 1965], No. 26655/66. Headings F2D and F2L. A transmission for a vehicle such as a bulldozer comprises a main modulated clutch and a change-speed and reverse constant-mesh gear, the main clutch and the gear clutches being engaged by hydraulic pressure controlled by solenoid valves which are controlled by transistorized circuits such that the main clutch is disengaged automatically at the commencement of gear shift and is re-engaged at a controlled rate on the completion of shift, the degree of engagement of the clutch being determined by the position of a clutch pedal and by the axial position of a gear lever which has a pivotal movement to select a ratio and a rotary movement about its own axis to select forward or reverse. The control circuits function to inhibit shifts to give a direction of travel opposite to that in which the vehicle is travelling above a predetermined speed of travel, and function to disable the inhibit control in the event of brake failure, and to permit run back manoeuvres, i.e. to permit the vehicle to run back down a hill with main clutch disengaged but a ratio established, and to engage the main clutch to drive the vehicle back up the hill provided the gear is not shifted. In the embodiment shown in Fig. 3, a main modulated clutch 13<SP>1</SP> is followed by a hydraulic torque converter 14<SP>1</SP> and change speed gear 16<SP>1</SP> comprising a reversing gear followed by a threespeed gear to give three forward and three reverse speeds. In this embodiment a brake B1 stations the change speed gear input shaft 40<SP>1</SP> during shift of the gear clutches to lessen the forces acting on these clutches during engagement. The clutches are engaged by fluid pressure under the control of solenoid valves controlled by transistorized circuits such that shift of the reversing gear is inhibited if the vehicle is moving in the opposite direction above a predetermined speed, the inhibit control being disabled in the event of brake failure. Provision is also made for roll back manoeuvres. The main clutch 13<SP>1</SP> is disengaged upon initiation of gear shift, the selected ratio clutch is then engaged, the selected direction clutch engaged and the main clutch re-engaged, in that order. A gear shift lever is pivoted to select a ratio or neutral, rotated about its own axis to select forward or reverse, and shifted axially to control the degree of engagement of the main clutch jointly with a clutch control pedal. In the neutral position of the gear lever engagement of the main clutch is permitted for testing or other purposes with the ratio and direction clutches disengaged. The direction clutches are also engageable in neutral to enable a power take off shaft (not shown) to be driven in either direction from a gear wheel 123<SP>1</SP>. A circuit for a starter motor 11<SP>1</SP> is so connected to the clutch control circuits that the clutches are disengaged during starting so that the starter can be operated with the gear lever in any position, the drive being disconnected, and the drive can only be connected after having shifted the gear lever to its neutral position to activate the control circuits.