Patent GB-780767-A (GB)
Title: Improved change speed mechanism for gear boxes
IPC: F16H3/12
Filed: 1955-03-29
Abstract: 780,767. Change-speed gearing. ZENS, P. M. F., and HONNORE, M. A. J. March 29, 1955 [March 31, 1954; Jan. 28, 1955], No. 9197/55. Class 80 (2). [Also in'Group XXIX] A change-speed gear, of the type comprising a main clutch or fluid coupling and a main brake on the driving side of the gear, and an auxiliary clutch and a further brake on the driven side, is characterized by a locking means actuated by the main brake and preventing a change of ratio until the gear has been rendered substantially stationary, the auxiliary clutch being a freewheel and the auxiliary brake being applied so lightly that the driven shaft of the gear is allowed to rotate slightly in order to facilitate change of mesh of the gears. In one form, a prime mover 2, Fig. 1, drives a fluid coupling 1 having an output shaft 4 which can be stationed by a brake 3 and is connected to the driving shaft 5 of a change-speed gear 6. The ratios in the gear 6 can be changed either by sliding its gears axially, or by changing the engagement of internal clutches. The gearing has a countershaft 7 which can be stationed by a brake 11 and drives a shaft 8 connected through a freewheel 9 to the road wheels of a motor vehicle. The brakes 3, 11 are applied when air under pressure is supplied to a single-acting piston 14 connected through linkwork to the two brakes in such a way that the brake 3 is applied hard but the brake 11 is applied only moderately. Compressed air can be supplied to the singleacting piston 14 from a source 37 through a three-way cock 16, a conduit 21 and an automatic valve 36. Compressed air is simultaneously supplied to a single-acting piston 15 connected through the linkwork shown to the throttle 46 of the prime mover 2. The throttle is thereby closed and the prime mover caused to idle. The reaction element of the brake 3 is secured to an arm 22, Fig. 4, which abuts a resilient stop 23 and a valve 24 in a conduit 25, 38. While a ratio is engaged, compressed air is supplied from the three-way cock 16 through a conduit 27, an automatic valve 26 and a conduit 28, to a cylinder 29 and a single-acting piston 30 which applies detents 32 to sliding selector rods 39 in the change-speed gear 6. To select and engage another ratio, a crank 19 is turned to cause a cam 17 to act upon the cock 16 to supply compressed air to the single-acting pistons 14, 15 and thereby idle the prime mover and apply the brakes 3, 11. At the same time, the singleacting piston 30 maintains the detents 32 in engagement with the selector rods 39. The reaction torque of the brake 3 upon the arm 22 opens the valve 24 and thus changes the setting of the automatic valve 26 so that compressed air is supplied therethrough to the cylinder 29 containing the single-acting piston 30. Thus, whatever the setting of the three-way cock 16, as long as a torque is absorbed in the brake 3, the single-acting piston 30 is applied with compressed air and the detents 32 prevent movement of the selector rod. When the driven shaft of the fluid coupling 1 has been brought to rest, the resilient stop 23 restores the reaction arm 22 of the brake 3 to its original position and closes the valve 24. The cylinder 29 is then connected to exhaust through the conduit 28 and the valve 26, which has been automatically adjusted to connect with the conduit 27 and the three-way cock 16. Accordingly, the detents 32 are withdrawn from the selector rods, and on further rotation of the crank 19, compressed air is admitted through a valve 115 to a servomotor 12 which stresses a spring 13 and slides the appropriate selector rod to engage the gear. The piston 30 is connected to a valve 34, which it opens when the detents 32 are withdrawn from the selector rods, to supply compressed air through the automatic valve 36 to the single-acting pistons 14, 15 and thus keep the brakes 3, 11 applied. When the selected gear has been engaged, the detents 32 are re-engaged with the selector rods, the valve 34 is closed, the single-acting pistons 14, 15 are connected to exhaust, the brakes 3, 11 are released and the prime mover again takes up the drive. A preferred form of positive clutch for use in the change-speed gear 6, when it is of the constant-mesh type, has teeth 42, 43, Fig. 3 some of which teeth 42a, 43a are longer than their neighbours. Thus, " pre-engagement " is effected by the long clutch teeth before the clutch is completely engaged. In a type of constant-mesh change-speed gearing suitable for use with a control system as described above, a prime mover drives through a fluid coupling or main clutch and an intermediate clutch 50, Fig. 2, to a hollow input shaft 51. Gears 53, 54 fast thereon mesh with gears which can be selectively connected by a clutch 87 to a countershaft having gears 83, 84 clutchable thereto and meshing gears 85, 86 on an output shaft 82 driving through a free-wheel (not shown) to the road wheels of a vehicle. The input shaft 51 can be stationed by a brake 57 applied when compressed air is admitted through a conduit 68 to a cylinder 52. Application of the brake 57 simultaneously disengages the clutch 50. A gear 112 meshes the gear 83 and, on application of the brake 57, is lightly braked by an auxiliary brake 111 to station the counter and output shafts of the gear. The reaction element 57a of the brake 57 is supported by springs 60, 61, Fig. 5, on a part 58 of the gear casing. The reaction element 57a bears on a resilient catch 58a having an end pin 62 adapted to engage in a locking drum 63. The drum 63 is normally locked in position by a spring-biased detent 64 withdrawn therefrom when compressed air is admitted through a conduit 67 to a cylinder 66. The conduit 67 is connected to the conduit 68 through which compressed air is supplied to the cylinder 52 controlling the engagement of the brake 57 &c. Change of ratio in the gearing is effected by turning cams 55, Fig. 6, which actuate the ratio selecting clutches within the gearing. The cams 55 are normally prevented from turning by the locking of the drum 63 as described above. To engage another ratio, a shaft 90 is turned to stress a torsion rod 93 connected at its end to the hollow shaft supporting the cams 55. A disc 94, Fig. 7, on the shaft 90 is provided with springs 95 engaging a disc 96 loosely splined on the shaft 90 and abutting a disc 97 fast on the inner end of the hollow cam-supporting shaft. The disc 96, Fig. 10, is provided with two holes 106, 107, and a groove 105 which can co-operate with two holes 103, 104, Fig. 9, in the disc 97 in turn co-operating with inner and outer annular grooves 101, 102, Fig. 8, in a non-rotating valve seating 98. Compressed air can be fed into the gap between the discs 94, 96 through a conduit 69, the outer annular groove 101 is connected to the conduit 68 through a port 100, and the inner annular groove 102 is connected to exhaust through a port 99. On turning the shaft 90 to pre-stress the torsion bar 93 as already described, the disc 96 turns relatively to the disc 97, which is retained in position by the locked drum 63, and compressed air passes through the hole 106 therein to the hole 103 in the disc 97 and thence through the port 100 to the conduit 68. The clutch 50 is thereby disengaged and the brakes 57, 111 are applied simultaneously, the detent 64 is withdrawn from the drum 63 and a detent 92 is applied to a locking drum 91 on the shaft 90. However, the absorption of torque in the brake 57 causes the reaction element 57a to be biased downwardly against the force of the spring 61 to engage the detent 62 with the drum 63, which is thereby held locked until the shaft 51, &c., has come to rest. When the detent 62 releases the drum 63, the cam-supporting shaft is turned by the torsionally stressed rod 93 and the selected gear is engaged by its cam 55. As the cam supporting shaft turns, the disc 97 turns with it, and the outer annular groove 101 is connected by the hole 103 to the diagonal groove 105 in the disc 96 which is in turn connected through the hole 104 to the inner annular groove 102 and thence via the port 99 to exhaust. Accordingly, the conduit 68 is connected to exhaust, the detent 64 is re-engaged with the locking drum 63 and the detent 92 disengages from the locking drum 91. While the change of engagement of ratio selecting clutches is taking place, the springs 60, 61 cause the brake reaction element 57a to oscillate, so that the facing clutch engaging elements are similarly oscillated and their engagement thereby facilitated.