Patent GB-821058-A (GB)
Title: Improvements in or relating to transmission system for tractors
Inventor: DEMOCRATIS ACHILLES JOHN
IPC: B60K31/00
Filed: 1956-07-23
Abstract: 821,058. Change-speed gear. FORD MOTORCO. Ltd. July 23, 1956, No. 22693/56. Class 80 (2). [Also in Groups XXIX and XXXI] In a tractor transmission, a gear additional to the normal variable speed gear has its ratio changed by engine speed and the operative engine speeds are varied by the tractor draw-bar pull. As shown, an auxiliary two-speed gear disposed between the engine and the main change-speed gear comprises a carrier 4, carrying integral planet gears 3, 7 and connected to a shaft 1 which is driven from the engine through a clutch. The gear 3 meshes with a sun gear 5 on a shaft 2 continuously driven from the engine and driving a power take-off (not shown), and the gear 7 meshes with a sun gear 6 on the input shaft 8 of the main change speed gear. Associated with the carrier 4 is a brake band 9, whereby with the band inoperative and the clutch engaged the shaft 8 is driven at the same speed as the shafts 1, 2, and with the band operative and the clutch disengaged the shaft 8 is driven at a reduced speed compared with the shaft 2. If both the band is operative and the clutch engaged, the mechanism forms a transmission brake. The band 9 is applied by pressurizing a cylinder 58, Fig. 8, and the clutch is disengaged by pressurizing a cylinder 49 containing a piston 51 adapted to engage a clutch operating fork 52. Thus, " low " speed is engaged by pressurizng a pipe 48 leading to the cylinder 49 and having a branch 56 connected by a valve spool formed by the rod 54 of the piston 51 to a pipe 57 leading to the cylinder 58. Relaxing of the pressure in the pipe 48 causes movement of the piston 51 and rod 54 to the right in Fig. 8, whereby the fork 52 is moved in an anticlockwise direction and the pipe 57 is connected through the valve to an exhaust port 59, thus engaging the " high " or direct speed. The pipe 48 is connectable by a valve 36, Fig. 6, to either a pipe 45 connected to a power of source or to an exhaust port 43, the valve comprises a spool 35 having axial grooves 41, 42 and the groove 42 being connected by ports 44 to the exhaust 43. The spool 35 is reciprocated by a lever 31, Fig. 4, pivoted at 32 and connected at 34 to a link 33 from an implement connected to the tractor for transmitting a thrust proportional to the implement drag. The lever 31 is also connected to a rod 29 carrying a piston 28 in a cylinder 27. A pipe 12 connects the cylinder 27 to a pump 11 driven by the tractor engine and includes a safety valve 13 and a leak control 14 which includes a V-shaped exhaust opening 18 the size of which is varied by a plunger 21 reciprocated by a hand lever 22, the pipe 12 being connected to the cylinder 27 by a damper valve 26 adapted to be closed by a transient implement pull on the link 33. Thus, the lever 31 is operated by an unbalance between engine speed, which causes a variation in the output of pump 11, and the implement drag, which causes a variable pull in the link 33. The effect of engine speed on the lever 31 can be varied by the leak control 14 having three positions 23, 24, 25 of the lever 22. In position 25 of the lever 22 there is a maximum engine thrust on the piston 28 and the auxiliary gear is set to its high speed condition. With the lever 22 in position 23 there is a maximum leak from the control 14 and hence implement reaction is always sufficiently great to overcome the engine speed thrust on the piston 28 and the auxiliary gear is set in its low speed position. With the lever 22 in position 24 the engine speed pressure on the piston 28 is sufficient to balance the maximum implement drag when the engine speed is normal and hence the auxiliary gear is in its high gear condition, but should the engine speed drop the low gear is engaged and when subsequently the engine speed rises high gear is re-engaged. In a modification, Figs. 9 and 11, the piston 28 is formed integrally with a four-landed valve spool 67 and a plunger 64 which is subjected to the pressure in a pipe 62 connected to a cylinder 61 of an automatic clutch release mechanism controlled by implement drag. The spool 67 co-operates with exhaust ports 81, 82 and pipes 78, 79 which are connected to opposite ends 88, 89 of a cylinder containing a three-landed plunger 86 and cooperating with pipes 93, 48 and exhaust port 94 corresponding to the pipes 45, 48 and port 43 in Fig. 6. In a further modification, Fig. 12, the pump 11 is connectable to the pipe 12 and to a pipe 120 leading to the tractor power lift mechanism by a valve 102 acted on by a spring 103 and pressure in a chamber 114 and a non- return valve 106 is interposed between the valve 102 and pipe 12. The valve 106 connects the valve 102 to a chamber 107 from which leads the pipe 12, a conduit 109 and a spring-loaded accumulator cylinder 108 carrying a valve spool 112. With a low pressure in the cylinder 108 the spool 112 connects the conduit 109 to a conduit 113 leading to the chamber 114 whereby the pump is connected to the pipe 120 leading to the power lift mechanism. With a high pressure in the cylinder 108 the spool 112 is moved to connect the conduit 113 as shown in Fig. 12 to atmosphere whereby the chamber 114 is exhausted and the valve 102 descends to connect the pump 11 to the chamber 107. In another modification, Fig. 2 (not shown), the pipe 12 is connected to a cylinder on the piston rod side of a piston, the piston rod being subjected to a pull proportional to implement drag. The valves in the embodiments may be mounted in a single casing with the lever 22 protruding to a position convenient to the driver. Specification 622,166, [Group XXIX], is referred to.