GBA20 gearbox with power shuttle – Shuttle

The Power Shuttle consists of two electrohydraulically controlled clutches. It is designed to enable direction of travel reversal under load. The Power Shuttle transmits the drive from the engine to the layshaft mounted on the front of the main gearbox by means of gears located respectively at the rear of the unit and at the gearbox input. A lever located to the left under the steering wheel, controls the Power Shuttle. Depending on the position selected by the operator (forward, neutral, reverse), the lever manages the proportional solenoid valves of the forward and reverse clutches by means of the tractor electronic system. The solenoid valves are located at the front and to the right of the gearbox on a clutch unit containing the Speedshift hydraulic control system. A filter element (60 microns) located under the selector cover plate, upstream from the clutch unit, provides additional filtering of oil supplying the solenoid valves (clutches, Speedshift). A potentiometer sensor screwed to the gearbox housing sends information on shaft rotational speed to the electronic system.

Shifting of any forward ratio to the corresponding reverse ratio, or vice versa, is easy without declutching or stopping the tractor. This "assisted" reversal enables gradual changing of the operating direction, even at high travel speeds without abrupt changes in speed. The clutches slow down tractor movement until the required speed is reached so that the direction of travel can be reversed.
The conventional hydraulically operated clutch pedal is replaced by an electrohydraulically operated manoeuvring pedal. This pedal modulates the pressure in the forward or reverse clutches through the tractor electronic system and thus facilitates precise movements such as implement hitching.

The forward and reverse clutches of the Power Shuttle are of different design.

Forward clutch
The forward clutch consists of:
- a conventional multidisc wet clutch consisting of a bell (33), the rear face of which is splined to assemble the input sun gear (53);
- an input shaft (19) crossing the spacer (4) which separates the engine flywheel from the transmission oil. The shaft is constantly meshed with the damper secured to the engine flywheel. It is splined so as to rotate with the clutch unit (18) which comprises the intermediate plates (30) and the discs (29) in which the piston (28) travels,
- a drive hub (27) comprising the discs (29), which is attached to the primary shaft (55). The forward clutch is centred in the cover plate (38) of the reverse clutch by the ball bearing (32).

Reverse clutch
The reverse clutch consists of:
- an epicyclic gear train consisting of three double planet gears (52) and three single planet gears (59),
- a hydraulic braking device for the planet carrier (49),
- a cover plate (38) supporting the forward clutch and with an inner face machined for fitting hydraulic components. The double and single planet gears (52) (59) of the epicyclic gear train mesh respectively on the input and output sun gears (53) (58). The pins (50) are idle-mounted and held in the planet carrier by plates (63). A central drilled channel and radial ports supply lubrication to the needle roller bearings (60). The planet carrier braking device consists of an annular piston (39) and a plate (43) that is loaded by springs (62) and discs (47) splined to the planet carrier. The intermediate plates (46) are immobilised by the pins (71).

Fixed unit
The fixed unit (1) has two functions:
- it receives the low pressure supplying the forward clutch via the pipe (74),
- it acts as a housing for the clutch lubrication and cooling pump.
The pipes (31) connecting the unit (1) and the cover plate (38) lubricate the reverse clutch braking device. The shims (3) fitted between the closing spacer (4) and the fixed unit (1) provide axial clearance for the forward clutch.

Drive transmission

Drive from the Power Shuttle is transmitted to a mechanical component located in the rear compartment of the input box. This component comprises a secondary shaft (1) attached to the gear (2) by splines. The shaft is fitted on two tapered roller bearings "R", and is supported by two bearings of the input unit. The shims (3) fitted between the cover plate and the unit are used to preload the bearings.

Operating principle

Forward clutch
When the lever under the steering wheel is in the Forward position, the relevant solenoid valve is activated and supplies a pressure that moves the piston (28). This, in turn, compresses the intermediate plates (30) and the discs (29) against the bell (33). The movement from the engine to the gearbox complies with the following drive train:
- input shaft (19) splined to unit (18),
- unit (18);
- intermediate plates (30);
- discs (29) compressed by the piston (28);
- hub (27),
- primary shaft (55),
- main gearbox layshaft via the input gear.
Simultaneously, the pressure applied behind the piston (39) of the braking device drops and the planet carrier assembly (discs (47), intermediate plates (46) and epicyclic gear train) rotate freely.

During forward operation, the oil flow from the centre housing via the pump (14) is directed towards the intermediate plates (30) and the discs (29) via the ports of the forward clutch unit (18) opened by movement of the piston (28). At the same time, lubrication of the braking device of the planet carrier (discs (47) and intermediate plates (46)) of the reverse clutch is interrupted.

Reverse clutch
When the previously mentioned lever is moved from the Forward to Reverse position, the solenoid valve concerned is activated and supplies the piston (39) of the braking device of the planet carrier. The piston then presses on plate (43) which compresses discs (47) and the intermediate plates (46) against the front cover plate of the input unit and stops the rotation of the planet carrier assembly. The drive from the engine is directly transmitted to the bell (33) splined to the input sun gear (53), without passing through the discs and intermediate plates of the forward clutch. Simultaneously, the oil pressure in the chamber of the piston (28) drops and frees the discs (29) and intermediate plates (30).
The input sun gear (53) then drives the double planet gears (52) freely mounted on the pins (50) which, in turn, drive the single planet gears (59) thus reversing the rotation of the output sun gear (58) splined to the primary shaft (55). The primary shaft then transmits the drive from the engine to the main gearbox layshaft via the input gear. A valve screwed to the top section of the cover plate (38) creates a small permanent bleed starting from 13 bar to provide an automatic bleed of the piston supply system (39).

As the piston (39) moves, it operates spools (44) that act as valves and compress springs (45) via the plate (43). The spools have a drilled centre channel and radial ports, allowing oil to flow to the channels in the cover plate (38) and the channels in the front cover plate of the input unit, thus lubricating the discs (47) and the intermediate plates (46). Lubrication of the mechanical components of the epicyclic gear train is via the lubricating system of the input unit. At the same time, the lubricating oil flow to the discs (29) and intermediate plates (30) of the forward clutch is interrupted, thus preventing any possible drive to the discs due to a "drag" effect.

Neutral position
In neutral position, the supply to the solenoid valves is cut, placing the forward and reverse clutches at rest and eliminating transmission of the engine drive to the gearbox. The lubrication flow is also interrupted. The pressure inside the system opens the valve and directs the oil to the housing. After changing a solenoid valve or its coil, the Power Shuttle hydraulic unit, the unit or one of its components or the electronic controller, it is necessary to calibrate the clutches.

Parts list 
(1) Pump unit (2) Pump cover plate (3) Shim(s) (4) Spacer (5) Locking ring (6) Splined ring (7) "O" ring (8) Anti-extrusion rings (9) Snap rings (10) Seal (11) Circlip (12) Ball bearing (13) Screw (14) Lubricating pump (15) Seal rings (16) Ring (17) Centring pin (18) Forward clutch unit (19) Input shaft (20) Pin (21) Circlip (22) Ball bearing (23) Snap ring (24) Seal (25) Belleville washers (26) Index holes (27) Drive hub (28) Forward clutch piston (29) Forward clutch discs (30) Forward clutch intermediate plates (31) Lubrication pipe (32) Ball bearing (33) Forward clutch bell (34) Planet carrier cover plate (35) Rivets
(36) Seal (37) Cover plate (38) Reverse clutch cover plate (39) Reverse clutch piston (40) Rivets (41) Seal (42) Seal (43) Plate (44) Spools (45) Springs (46) Reverse clutch intermediate plates (47) Reverse clutch discs (48) Ring restrictor (49) Planet carrier (50) Planet gear pins (51) Spacers
(52) Double planet gears (53) Input sun gear (54) Snap ring (55) Primary shaft (56) Snap ring (57) Ball bearing (58) Output sun gear (59) Single planet gears (60) Needle roller bearings (61) Snap rings (62) Springs (63) Stop plates (64) Screw (65) Snap ring (66) Screw (67) "O" ring (68) Ball bearing (69) Seal (70) Screw (71) Pins (72) Union (73) 1.5 bar valve (74) Pipe (75) "O" rings (76) Pipe (77) Screw (78) Pipe (79) Screw (80) Flange (81) Seal (82) Strainer (83) Cover plate (84) Plug (85) Seal (86) Pipe (87) Pipe (88) Transfer pipe (89) Seal (Loctite) (90) Diagnostics connector (lubrication) (91) Union
(92) "O" rings (93) Union (94) Pipe (95) "O" rings (96) Dust seal (97) Screw (98) Snap ring (99) Screw (100) Ring (101) Elbow union