GBA25 - Robotic mechanical gearbox


The GBA25 gearbox is equipped to tractors with Dyna 4 transmission. This transmission is fully automated. It allows shifting between all the ratios without declutching. The gearbox is divided into two parts:
- The Powershift module, with four ratios for shifting under load.
- The robotically-controlled mechanical gearbox with four ranges.
The transmission assembly is controlled electronically by an Autotronic 5 calculator. The GBA25 Dyna-4 gearbox has 16 ratios. These are provided by 4 Powershift module ratios for shifting under load, and 4 mechanical gearbox ranges. The mechanical gearbox ranges are controlled like a ratio for shifting under load. The ratios are controlled by two levers:
- Power control lever located under the steering wheel.
- gear shift lever located on the armrest.
The mechanical gearbox is located between the Powershift module and the rear axle. It comprises two shafts (upper and lower shaft lines), on which four gear trains with helical teeth rotate. Input drive is supplied by the Power Shuttle and is transmitted to the upper shaft line. Output drive is transmitted via the lower shaft line to a creeper unit or directly to the crown wheel and pinion.

Lubrication
The lubricating oil coming from the 5 bar valve of the tractor is sent to the gearbox lower shaft line and upper shaft line. A network of internal channels directs the oil to the elements requiring lubrication.


Selecting ratios




Ratios are selected using two synchronisers, one single cone and one double cone. Each synchroniser is engaged individually. The synchronisers are controlled by two selector rails and two forks. Each selector rail has a double-acting piston, allowing range shifting. The selector rail pistons are controlled hydraulically via the tractor 20 bar circuit. Four solenoid valves (L52, L53, L54, L55) located on the right-hand side of the gearbox control selector rail movement. Four switches (L56, L57, L58, L59) inform the calculator of the selector rail positions. The switches are pressed in by pins (130). Each range has a corresponding solenoid valve and switch.


Parts list
(1) Primary shaft (2) Bearing cone (3) Bearing cup (4) Shims (5) Gearbox housing (6) Cover (7) Shims (8) Bearing cup (9) Bearing cone (10) "O" ring (11) Spring (12) Lubrication pipe (13) Secondary shaft
(14) Spacer (15) Circlip (16) Washer (17) Shims (18) Circlip (19) Washer (20) Shims (21) Bearing cup (22) Bearing cone (23) Bearing cone (24) Bearing cup (25) Pinion (26) Double pinion (27) Bearing cup (28) Bearing cone (29) Bearing cone (30) Bearing cup (31) Pinion (32) Needle bearing (33) Washer
(34) Circlip (35) Circlip (36) Spacer (37) Needle bearing (38) Needle bearing (39) Spacer (40) Circlip (41) Shims (42) Circlip (43) Pinion (44) Spacer (45) Pinion (46) Bearing cone (47) Bearing cup (48) Pinion
(49) Ring (50) Bearing cone (51) Bearing cup (52) Deflector (53) Ring (54) Sliding coupler (55) Ball bearing (56) Pressure connector (57) Brake (58) Spring (59) Flange (60) Hub (61) Ball bearing (62) Pressure connector (63) Ring (64) Spring (65) Brake (66) Cone (67) Flange (68) Snap ring (69) Hub
(70) Sliding coupler (71) Power take-off shaft (72) Fork (73) Selector rail (74) "O" ring (75) "O" ring (76) Circlip (77) Sleeve (78) "O" ring (79) "O" ring (80) Plug (81) "O" ring (82) Circlip (83) "O" ring (84) Circlip (85) Plug (86) "O" ring (87) Circlip (88) Sleeve (89) "O" ring (90) "O" ring (91) Snap ring
(92) Piston (93) Spring (94) "O" ring (95) "O" ring (96) Fork (97) Pin (98) Selector rail (99) Castellated nut (100) Screws (101) Castellated nut (102) Plate (103) Screws (104) Rail (105) Locknut (106) Rail
(107) Screws (108) Castellated nut (109) Castellated nut (110) Screws (111) Plate (112) Circlip (113) Shims (114) Bearing cup (115) Bearing cone (116) Pinion (117) Bearing cone (118) Bearing cup (119) Pinion (120) Circlip (121) Shaft (122) Bearing (123) Powershift module cover (124) Reverse pinion hub (125) Pin (126) Plug (127) Plug (128) "O" ring (129) "O" ring (130) Pin (131) Reverse pitch nut

Description and kinematics of ratios

The robotic gearbox allows four ratios to be obtained with only four gear trains, two shafts and two synchronisers.

Kinematics 



Range 1

The reduction is carried out on three gear trains. The first gear train drives the second train via the 1st gear synchronisers, then the third train.


Range 2

The reduction is carried out on the first gear train. The 2nd gear synchronisers secure the 2nd gear pinion to the secondary shaft.


Range 3

The reduction is carried out on the third gear train. The primary shaft is secured to the 3rd gear pinion by the 3rd gear synchronisers.


Range 4

The reduction is carried out on the fourth gear train. The primary shaft is secured to the 4th gear pinion by the 4th gear synchronisers.

In forward position, input drive comes directly from the Power Shuttle to the primary shaft (1). In reverse position, drive comes from the Power Shuttle via the pinions (124), (119) and (116) and the shaft (121). It enters via the second driven pinion (25), which is constantly meshed to the primary shaft (1).

Primary shaft 
The primary shaft (1) is splined to the Power Shuttle forward hub. It is supported by two taper roller bearings (3)(4) and (50)(51) Adjustment is controlled by shims (4). The PTO shaft (71) is inserted through the centre of the primary shaft (1). This cavity in the shaft (1) also serves as a channel for lubricating oil.
The first and second driving gear is cut into the primary shaft (1). The double pinion (26) turns idle on the shaft (1) and is supported by two taper roller bearings (27)(28) and (29)(30) and two needle bearings (37)(38). This pinion is supported on the shaft by shims (20). The fourth driving gear turns idle on the shaft (1). It is supported by a lubricated bush (49).


Secondary shaft
The secondary shaft (13) turns on two taper roller bearings (8)(9) and (46)(47). Bores in the centre of the shaft (13) ensure proper lubrication. Adjustment is controlled by shims (7). The pinion (25) turns truly on the shaft (13) and is supported by two taper roller bearings (21)(22) and (23)(24) and a needle bearing (32). The pinion (25) acts as a bearing to the idle pinion (31). This pinion (31) is in direct contact with the pinion (25). A layer of oil ensures the mating faces are lubricated. The pinions (43) and (45) are splined to the shaft (13). They are separated by a spacer (44).


Synchronisers
The single cone synchroniser located on the primary shaft (1) allows shifting between the third and fourth gears. Its hub (60) is splined to the shaft (1). It is held in position by a circlip (42) on one side and by the bearing cone (50) fitted tightly on the shaft (1). By moving the slider (54), the shaft (1) is locked either:
- with the double pinion (26) (3rd)
- with the pinion (48) (4th).
The double cone synchroniser located on the secondary shaft (13) allows shifting between the first and second gears. Its hub (69) is integral with the pinion (25). It is held in position by the snap ring (68). By moving the slider (70), the shaft (13) is locked either:
- with the idle pinion (31) (1st)
- or with the pinion (43) (2nd).

Selecting ratios 
The synchronisers are controlled conventionally by forks (72) and (96) and selector rails (73) and (98). The selector rails are controlled hydraulically. The selector rails are controlled by double-acting pistons.
On the selector rail (98) that controls the 1st and 2nd gear synchroniser, the piston (92) is damped by a spring (93) to give smooth shifting between ranges 1 and 2. The selector rails are adjusted by tightening or loosening the castellated nuts (99)(101) and (108)(109). Once adjusted, the stops are held in position by screws (100) and (107). An interlock mechanism comprising two rods (104)(106) and a locknut (105) prevents the selector rails from being engaged simultaneously. When one selector rail is engaged, the pin locks the other rail in a groove.