Patent GB-915854-A (GB)
Title: Improvements in and relating to the control of friction clutches in change-speed gears
IPC: F16D48/02
Filed: 1960-12-30
Abstract: 915,854. Change-speed gear and control; ratchet clutches. HURTH, H., and HURTH, F. Dec. 30, 1960 [March 18,1960], No. 44714/60. Class 80 (2). When changing down in a control for two-speed-adjacent, pneumatically or, as shown, hydraulically operated, friction clutches 18, 28, in a two, or more, speed change-speed gear for machine-tools, wherein at least the lower speed clutch 28 comprises a oneway device so as to release on overrun of its driven member, the hydraulic pressure on the higher speed clutch 18 is first reduced to a value which allows slipping whilst still maintaining some tractive effort in that clutch, and then, under the automatic control of the lower speed clutch, is caused to disappear completely after said lower speed clutch takes up the drive. The change-speed gear shown in Fig. 1 comprises lower speed gears 12, 25, respectively, fixed on the input shaft 10 and an intermediate shaft 24 clutchable to an output flange 27 through the lower speed clutch 28, and higher speed gears 13, 26 respectively clutchable to the input shaft 10 through the higher speed clutch 18 and fast with the output flange 27. Such change-speed gears may be arranged in series, as shown in chain-dotted lines. The higher speed clutch 18 comprises discs 16 alternately splined to an inner member 17 fixed on the shaft 10 and a cylindrical extension 14 of the gear 13 and grippable between a flange of the member 17 and an axially movable presser plate 20 which together with an axially fixed piston 19 constitutes a servomotor 21. Springs 22 disengage. The lower speed clutch 28 comprises discs 31 alternately splined to an inner member 32, in screw-threaded engagement with the intermediate shaft 24, and a cylindrical extension 29 of the gear 26 and grippable between a flange 80 of the member 32 and an axially movable presser plate 36 which together with a piston 35 constitutes a servomotor 37, the axial engaging movement of the presser plate being limited by a stop 82. Springs 38 disengage. The hydraulic control system comprises a pump 51 feeding to an electromagnetic valve 45 through a line 50 and a valve 90 maintaining a minimum pressure in the line 50, to an electro - magnetic valve 57 through a line 63, and to the higher speed clutch servomotor 21 through a line 91, an inflow valve 92 closed by a spring 93, a chamber 94 and a line 23. An adjustable spring-loaded valve 64 relieves to a sump 68. A control valve 41 comprises a piston 42 having lands 113, 114, 115 which is movable against an hydraulic cushion, or, as shown, an adjustable spring 43 by pressure in a line 53 connected to the valve 57 through an adjustable throttle 54, and a line 56. Between the lands 113, 115, the control valve 41 is connected to the electromagnetic valve 45 through a line 44 having an air chamber 72. A line 40 connects the control valve 41 with the lower speed clutch servomotor 37. An outflow valve 95 formed with, or abutting, the valve 92 is urged by the spring 93 to close against a valve seating of a piston bush 96 through which pressure can exhaust when the valve 95 is open, an exhaust port 98 being provided. A loading piston 99 is connected to the piston bush 96 by a loading spring 100, moves in a cylinder 106 connected to the control valve 41 through a line 107, and is limited by a shoulder 101 and by a stop-screw 102 adjustable in a stop-piston 103 loaded by an adjustable spring 104. A space 108 adjacent the stoppiston 103 and remote from the spring 104 is connected to the line 40. In the lower speed clutch presser plate 36 there is provided a valve 110 which is opened by a spring and closed by the discs 31 and has a spring-loaded ball outlet valve which, with the valve 110 open, determines a reduced pressure in said servomotor. Pressure-regulating means may be interposed in the lines 91, 40 and 23. In operation, in neutral the electromagnetic valves 45, 57 are de-energized to exhaust the lines 44, 56 ; the piston 42 is in its bottom position, the stop-piston 103 is in the rightward position shown, the loading piston 99 is pressed against the stop-screw 102 by the loading-spring 100 which abuts the piston bush 96 which in turn abuts the outflow valve 95, the outflow and inflow valves 95, 92 are kept closed by the spring 93, and for clutch disengagement the presser plates 20, 36 are leftwardly moved by the springs 22, 38 and the valve 110 is open. To engage the lower speed gear a switch 70 is closed to energize the electromagnetic valve 45 to feed the lower speed clutch servomotor 37, the land 113 blocking communication between the lines 44 and 107. The valve 110 closes to permit build-up of full pressure in the servomotor 37 and in the space 108. The stop-piston 103 is displaced to the left followed by the loading piston 99 bearing against the stop-screw 102 so that the spring 93 keeps the inflow valve 92 closed. To engage the higher speed gear a switch 71 is also closed so that the electromagnetic valve 57 is also energized to feed the line 53 under the piston 42 which is raised at a speed determined by the throttle 54. While the piston 42 is moving upwards, firstly both lines 40 and 107 are fed. The loading piston 99 is driven rightwardly as far as the shoulder 101 and opens, by means of the piston bush 96, the inflow valve 92 against the spring 93 to energize the higher speed clutch servomotor 21. As the result of the higher speed gear engagement the gear 26 overruns the shaft 24, the inner member 32 of the clutch screws to the right and since rightward presser-plate 36 movement is limited by the stop 82 the lower speed clutch disengages; valve 110 opens and pressure in the servomotor 37 and in the line 40 and the space 108 drops to the predetermined reduced value. The spring 104 pushes the stop-piston 103 to the right. The loading piston remains in its rightward terminal position although pressure in the line 107 and the cylinder 106 has also fallen. When the piston 42 is in its upper position shown, the land 115 separates the line 40 and 107 and the cylinder 106 again receives the full pressure. The servomotor 37 and space 108 are exhausted through a port 83 in the valve 41. To change down, the switch 71 is opened and the electromagnetic valve 57 is de-energized to exhaust pressure under the piston 42 which descends at a speed determined by the throttle 54. Firstly, the line 40, together with the line 107, is fed so that the presser plate 36 is rightwardly moved to the stop 82 but as the discs are rightwardly moved the valve 110 is open so that only the predetermined reduced pressure is established in the servomotor 37, the space 108 and the cylinder 106 and exerts no controlling influence. When the piston 42 reaches its bottom position and the land 113 separates the line 40 and 107 the space 106 is exhausted through a port 75 in the valve 41, the loading piston bears against the stop-screw 102, and the loading spring 100 is relieved to the extent that the inflow valve 92 is closed. The piston bush 96 held only by the loading spring 100 acts, with the stationary outflow valve 95, as a pressurereducing valve until a reduced pressure is established in the servomotor 21, the higher speed clutch slips and, with some tractive effort being maintained, the speed of the gear 26 drops until the drive through the gears 12, 25 takes over. The discs 31 bear against the presser-plate 36, the lower speed clutch takes over the drive, and the valve 110 closes so that full pressure in the servomotor 37 and the space 108 is built up. The stop-piston 103 is moved to the left and the spring 100 is completely relieved so that pressure completely disappears from the higher speed clutch servomotor 21. Alternatively, the initial pressure reduction in the higher speed clutch may be effected by a manually or electrically-actuated pressurereducing valve, and longitudinal motion of the one-way device in the lower speed clutch may then be used to completely open the pressurereducing valve by mechanical, electrical or hydraulic means.