1
4
3
2
8
9
5
6
10
11
7
12
5
Type 4/6THF5 | RE 64 557/02.07
Hydraulic function principle
The pilot control units with end position locks type THF5
operate on the basis of direct actuated pressure reducing
valves.
They basically comprise of control lever (1), four to six pressure
reducing valves, a housing (6) and locks.
Each pressure reducing valve comprises of a control spool (2),
a control spring (3), a return spring (4) and a plunger (5).
At rest, control lever (1) is held in its neutral position by return
springs (4). Ports (1, 2, 3, 4) are connected to tank port T via
drilling (8).
When the control lever (1) is deflected, plunger (5) is pressed
against return spring (4) and control spring (3). Control spring
(3) initially moves the control spool (2) downwards and closes
the connection between the relevant port and tank port T. At
the same time the relevant port is connected to port P via
drilling (8).
The control phase starts as soon as control spool (2) finds
its balance between the force from control spring (3) and the
force, which results from the hydraulic pressure in the relevant
port (ports 1, 2, 3 or 4).
Due to the ineraction between control spool (2) and control
spring (3) the pressure in the relevant ports is proportional to
the stroke of plunger (5) and hence to the position of control
lever (1).
This pressure control which is dependent on the position of the
control lever and the characteristics of the control spring
permits the proportional hydraulic control of directional valves
and high response valves for hydraulic pumps and motors.
A rubber boot (9) protects the mechanical components in
the housing from contamination, therefore, these pilot control
units are suitable for even the most unfavourable operating
conditions.
End position lock
Only those control ports, for which it is necessary to hold the
control lever in a deflected position are equipped with end
position locks (except control port 2).
Electro-magnetic lock
An additional spring (7), which is fitted below the prefeeling
point socket (12) warns, by means of an increased force, which
is required for compressing this spring, that the plunger (5)
and the control lever (1) have almost reached their end position.
When this threshold is overcome, the solenoid armature (10)
contacts the solenoid (11); if the solenoid is energised, then
control lever (1) is held in its end position by magnetic force.
This lock is released automatically when the solenoid is de-
energised.
port 2 port 4
Electro-magne-
tic lock
Symbol for the 4 THF 5
with 3 electro-magnetic locks
Functional description, section, symbol
(384 pages)
(144 pages)
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