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Massey Ferguson 5430 Tractors hydrostatic steering 125/160 cm3
The Massey Ferguson 5430, 5465, 5470, 5475 Tractors steering system is
of the dynamic type (constant 0.5l /min flow rate - 6 bar standby
pressure). Its control principle is of the Load Sensing (LS) type.
The Orbitrol steering unit (21) type is displayed on an adhesive plate
located below the steering unit. The steering unit has no mechanical
links, other than the steering column itself, between the steering wheel
and steering ram.
The system comprises the following main
components:
- a pressurised oil feed from the variable displacement pump;
- a steering unit that can be, according to the type of front axle:
- OSPF 125 LS dynamic,
- OSPF 160 LS dynamic;
- a double acting steering ram (1) with a different profile according to
the type of tractor or front axle.
The MF 5430, 5470, 5465, 5475 Tractors steering unit is supplied via the
priority block(s) (depending on version) by the high flow rate high
pressure circuit.
When the steering wheel is turned, the necessary flow of oil is directed
to the corresponding side of the steering ram.
The other side of the ram is connected to the gearbox selector cover
return ports.
In the event of a variable displacement pump failure, the steering unit
acts as a manual pump, thus allowing the tractor to continue to be
steered.
This operation, performed without hydraulic assistance, obviously
requires significant effort to turn the steering wheel.
Fig.27
Description of the steering unit
The steering unit comprises a selector spool valve, a spring centred
supply sleeve and a drive shaft linked to the steering column.
The Massey Ferguson 5465, 5430, 5470, 5475
Tractors steering unit comprises five ports:
- pressure;
- return to selector cover;
- two supplies (left and right) to the steering ram;
- Load Sensing
The circuit is protected by a safety valve, two shock valves and two
suction valves.
The principle of Load Sensing
Fig.28. MF 5430, 5465, 5470, 5475 Tractor Steering unit
(Orbitrol 125/160 cm3)
The LSD steering unit possesses a fifth LS
port. This port is connected:
- either to the closed steering unit circuit when steering is in neutral
position;
- or with the pressure supply line when the steering wheel is turned.
Fig.29. Parts list
(1) Screw (2) Screw (3) Seal (4) Closing plate (5) O’ring (6) Stator (7)
Cotter pin (8) O’ring (9) Rotor (10) Spacer (11) Link shaft (12) Washer
(13) Centring springs (14) Needle bearing (15) Bush (16) Washer (17)
O’ring (18) Relief valve (19) Seal (20) Shock valve (21) Orbitrol
steering unit (22) Non-return valve (23) Suction valves (24) Bush (25)
Spool valve (26) Non-return valve (27) Sleeve (28) O’ring (29)
Distributor plate
Layout of channels and ports
Fig.30. Parts list / Legend
1 - 2 WD or 4 WD axle (2 WD on figure shown), A - Double acting steering
ram, AV - Front axle face, B - Location of steering column, L - Supply
to left-hand union of the steering ram, LS - Signal to variable
displacement pump, P - Pressure, R - Supply to right-hand union of the
steering ram, T - Return to housing via gearbox selector cover
Neutral position (engine running)
In this position the spool valve (25) is centred in relation to the
sleeve (27) by the springs (13). The channels P1, L, R are not supplied.
The oil coming from the variable displacement pump via channel (2) is
directed in priority to the Orbitrol unit via channel (1). With the
steering in a neutral position, there is no flow in this channel. The
circuit is closed centre.
Two shock valves (20) and two suction valves (23) are located in ports L
and R of the spool valve. The shock valves (20) protect the circuit
between the steering
ram and the spool valve from over pressure caused by mechanical shocks to
the front wheels.
The suction valves (23) allow the oil released by the shock valves (20)
to pass from the right-hand channel to the left-hand channel or vice
versa depending on the
movement of the piston inside the steering ram.
Fig.31. Legend
A - Double acting steering ram, BP - Priority block(s), L - LH hydraulic
port of the steering ram, LS - Signal, P - Pressure, P1 - Supply to the
metering device, R - RH
hydraulic port of the steering ram, T - Return
Steering on lock position (engine running)
Fig.32
Action on the steering wheel (to the left or right) produces an angular
displacement of the spool valve (25) in relation to the sleeve (27) and
the opening of the closed
Orbitrol circuit.
The pilot flow coming from the Orbitrol enters via channel (4) thus
allowing for the flow required for the metering device (stator (6) and
rotor (9)) to pass into channel
(1).
The rotor (9) is rotated and directs back into the cylinder a quantity
of oil proportional to the angle of rotation. The rotor (9) turns
proportionally to the Massey Ferguson
MF 5465, 5470, 5475, 5430 Tractor steering wheel.
Example: Let us suppose that the steering wheel is turned by 5°. An
angular displacement of 5° of the spool valve (25) is produced in
relation to the sleeve (27). The
rotor (9) is driven in rotation as long as it is supplied. It drives
with it the link shaft (11) and the sleeve (27).
When the latter have turned 5°, the spool valve (25) and the sleeve (27)
are once again centred by the springs (13). The rotor ceases to be
supplied and stops.
This same reasoning applies to greater angles. The quantity of oil
delivered by the steering unit to the steering ram A is therefore
proportional to the rotational angle of
the steering wheel.
The spool valve (25) allows, whether steering lock is applied to the
left or right, to direct oil fed by the metering device (stator (6) and
rotor (9)) to port L or R.
During rotation, the sleeve (27) ensures the synchronous communication
of the cavities in the metering device with the circuit from the pump,
on the one-hand, and
the circuit to the steering ram, on the other hand.
A non-return valve (26) is screwed into the supply port of the steering
unit. This valve is one-way. It prevents excessive pressure exerted to
the front wheels from
being transmitted to the pump when the steering lock is applied.
If the pressure in the steering circuit is too high, the relief valve
(18), located in the steering unit, opens and the excess pressure is
released to channel T.
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