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Massey Ferguson 8240, 8250 gearbox - Dynashift with power shuttle
On Massey Ferguson 8240, 8250 tractors the Dynashift can also be mounted on an input unit fitted with a mechanical reverse shuttle.
This section only describes the Dynashift with power shuttle. The operating principles of the two Dynashift versions are similar.
However, housing profile of the Dynashift with power shuttle is
different because of the location of the power shuttle rear clutch and
the driving gear located at the rear end of the housing.
MF 8240, 8250 gearbox dynashift is located between the rear clutch and
the driving gear of the power.
It is a hydraulically controlled gear shift mechanism and provides the
gearbox with four input ratios.
The function is ensured by two epicyclic gear trains associated with two
hydraulic clutches.
Dynashift design enables selection of each of the four ratios while
driving, and under load, without declutching, using a lever mounted to
the left under the steering wheel.
(1) Secondary ring gear carrier (2) Intermediate plates (3) Front clutch
discs (4) Belleville washer (5) Splined hub (6) Needle bearing (7)
Transmission shaft (8) Ring restrictor (9) Screw (10) Friction washer
(11) Bearing (12) Washer (13) Front cover (14) Clutch housing (15) Front
brake discs (16) Thrust plate (clutch - brake) (17) Clutch plate (18)
Screw (20) Springs (21) Spacer casing (22) Front piston (23) Rivet (24)
O’ring (25) Screw (26) O’ring (27) Ball bearing (28) Primary planet
carrier (29) Rivets (30) Screw (31) Primary ring gear (33) Screw (34)
Secondary ring gear (35) O’ring (36) O’ring (37) Rear piston (38) Clutch
plate (39) Secondary planet carrier (40) Cover (41) Rear brake discs
(42) Screw (44) Clutch plate (45) Thrust plate (clutch - brake) (46)
Screw (47) Cover (48) Intermediate plates (49) Retaining ring (50) Rear
clutch discs (51) Friction washer (52) Belleville washers (53) Secondary
shaft (54) Splined hub (55) Circlip (56) Spacer (57) Ball bearing (58)
Ball bearing (59) Rear clutch housing (60) Retaining ring (61) Secondary
sun gear (62) Retaining ring (63) Needles (64) Primary sun gear (65)
Springs (69) Circlip (70) Stop (71) Shim(s) (72) Retaining ring (74)
Rivets (75) Oil splasher (76) Stud washer (77) Spring washer (78) Washer
(79) Locating pin
The Dynashift housing is controlled by two solenoid valves mounted on
the clutch unit located on the front right hand side of the gearbox.
The two solenoid valves are controlled by the MF 8240, 8250 tractor’s electronic system.
The Dynashift input unit comprises two epicyclic gear trains: the
primary epicyclic gear train is the input unit’s main component and
transmits the movement of the engine to the gearbox, the secondary
epicyclic gear train controls the speed of the primary sun gear.
Primary epicyclic gear train
The movement comes in via the primary ring gear (31) which is splined
onto the transmission shaft (7).
The ring gear turns at the same speed
as the engine.
The movement exits via the planet carrier (28) which is splined onto the secondary shaft (53).
The primary sun gear (64) is driven by the
secondary epicyclic train.
The speed of this sun gear determines the reduction ratio of the
gearbox.
Secondary epicyclic gear train
This epicyclic gear train is controlled by two Massey Ferguson 8250,
8240 hydraulic clutches and brakes.
The secondary ring gear (34) is:
- either locked onto the transmission shaft (7) by the three clutch
discs (3) and the Belleville washer (4) located in the front part of the
housing,
- or immobilized in relation to the housing by three brake discs (15)
and a piston (22).
- When there is no pressure, the piston (22) is pulled back by the
twelve springs (20) and the Belleville washer (4) by means of the thrust
plate (16).
- When the 17 bar pressure is built up in the circuit, the piston (22)
moves forward and blocks the brake discs (15) while pushing the thrust
plate (16) that
compresses the Belleville washer (4).
Speed of the secondary ring gear is established as follows:
- speed equals engine speed if the front piston is not under pressure.
- speed nil when the front piston is under pressure.
The secondary sun gear (61) is:
- either locked onto the secondary transmission shaft by means of four
clutch discs (50) and two Belleville washers (52) located on the rear
section of the housing,
or immobilized in relation to the housing by means of three brake discs
(41) and a piston (37).
- When there is no pressure, the piston (37) is pushed forward by the
Belleville washers and the six springs (65).
- The 17 bar pressure moves the piston (37) back and locks the brake
discs (41). The piston compresses the Belleville washers (52) by means
of the thrust plate
(45) that releases the secondary MF 8250, 8240 transmission shaft clutch
discs.
- Immobilization of either the secondary ring gear (34) or the secondary
sun gear (61) modifies the speed of the secondary planet carrier (39).
The latter drives the
primary sun gear (64), and this establishes the gearbox reduction ratio.
Explanation of the ratios
Ratio A: Reduction 1/1.620
The two pistons (22) (37) are simultaneously under pressure from the 17
bar circuit.
The secondary ring gear (34) is locked onto the casing by means of the
front brake.
The secondary sun gear (61) is locked onto the casing by the rear brake.
Consequently:
- the secondary epicyclic gear train is locked
- the primary sun gear (64) is locked
- the reduction ratio is only set by the primary epicyclic gear train.
- This is standard kinematics, movement comes in via the ring gear and
exits via the planet carrier; the sun gear does not move.
Ratio B: Reduction 1/1.386
Front piston (22) is under pressure.
Front brake locks the secondary ring gear (34) onto the casing.
Rear piston (37) is not under pressure.
The secondary sun gear (61) rotates with the secondary Massey Ferguson
8240, 8250 transmission shaft (53) (clutch engaged).
The secondary planet carrier (39) is rotating at a low speed, driving
the primary sun gear (64).
The rotational speed of the primary planet carrier (28) corresponds to
the speed difference between the primary ring gear (31) and the primary
sun gear (64).
Reduction effect is therefore minor.
Ratio C: Reduction 1/1.1704
Rear piston (37) is under pressure.
The rear brake locks the secondary sun gear (61) onto the casing.
The front piston (22) is not under pressure.
The secondary ring gear (34) rotates with the transmission shaft (7) thereby transmitting a higher speed to the secondary planet carrier (39).
The primary sun gear
(64) is driven by the secondary planet carrier (39) at a higher speed
than in ratio B.
Reduction is therefore lower.
Ratio D: Reduction 1/1 ratio
The two pistons are not under pressure. The two clutches are therefore
engaged.
The secondary ring gear (34) rotates with the transmission shaft (7).
The secondary sun gear (61) is locked on the secondary shaft (53)
thereby mechanically locking the entire system.
The ratio is therefore 1:1 (direct transmission).
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