P : From main pump T : To tank
P1 : Left reverse P2 : Left forward
P3 : Right reverse P4 : Right forward P5 : Travel signal P6 : Steering signal
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
12
1. Plate 2. Body 3. Piston 4. Collar
5. Metering spring
6. Centering spring 7. Valve
8. Damper 9. Steering signal
10. Steering signal valve spring
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
12
Unit: mm
No. Check item Criteria Remedy
1 Metering spring
Standard size Repair limit
If damaged or deformed, Free length x
Outside diameter
Installed length
Installed load
Free length
Installed load
26.5 x 8.15 24.7 16.7 N
(1.7 kg) — 13.7 N
(1.4 kg)
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
12OPERATION
1. At neutral
Ports A and B of the control valve and ports P1 and P2 of the PPC valve are connected to drain chamber D through fine control hole f in spool (1). (Fig. 1)
2. Fine control (neutral → fine control)
When piston (4) starts to be pushed by disc (5), retainer (9) is pushed. Spool (1) is also pushed by metering spring (2), and moves down.
When this happens, fine control hole f is shut off from drain chamber D. At almost the same time, it is connected to pump pressure chamber PP, and the pilot pressure of the main pump is sent from port A through fine control hole f to port P1.
When the pressure at port P1 rises, spool (1) is pushed back.
Fine control hole f is shut off from pump pressure chamber PP.
At almost the same time, it is connected to drain chamber D, so the pressure at port P1 escapes.
As a result, spool (1) moves up and down until the force of metering spool (2) is balanced with the pressure at port P1.
The relationship of the position of spool (1) and body (10) (fine control hole f is in the middle between drain hole D and pump pressure chamber PP) does not change until retainer (9) contacts spool (1).
Therefore, metering spring (2) is compressed in proportion to the travel of the control lever, so the pressure at port P1 also rises in proportion to the travel of the control lever. In this way, the spool of the control valve spool moves to a position where the pressure of chamber A (same as pressure at port P1) and the force of the return spring of the control valve spool are balanced. (Fig. 2)
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
12
3. Fine control (control lever returned)
When lever (5) starts to be returned, spool (1) is pushed up by the force of centering spring (3) and the pressure at port P1.
Because of this, fine control hole f is connected to drain chamber D, and the pressurized oil at port P1 is released.
If the pressure at port P1 drops too much, spool (1) is pushed up by metering spring (2), so fine control hole f is shut off from drain chamber D. At almost the same time, it is connected to pump pressure chamber PP, so the pressure at port P1 supplies the pump pressure until the pressure recovers to a pressure equivalent to the position of the lever.
When the control valve returns, oil in drain chamber D flows in from fine control hole f of the valve on the side that is not moving.
It passes through port P2 and goes to chamber B to charge the oil. (Fig. 3)
4. At full stroke
Lever (5) pushes down piston (4), and retainer (9) pushes down on spool (1). Fine control hole f is shut off from drain chamber D, and is connected to pump pressure chamber PP.
Therefore, the pilot pressure oil from the main pump passes through fine control hole f and flows to chamber A from port P1 to push the control valve spool. The return oil from chamber B passes from port P2 through fine control hole f and flows to drain chamber D.
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
12TRAVEL SIGNAL/STEERING FUNCTION
• Travel signal
If either of the travel levers is operated, the maximum PPC output pressure on both sides is output as the travel signal.
Accordingly, if the machine is traveling is judged by the signal of port P5.
• Steering signal
If the operation quantities of both levers are different from each other as in the steering operation, the higher one of the PPC output pressures on both sides is output as the steering signal.
Any signal is not output from port P6 while the machine is travelling straight (forward or reverse) or in neutral.
Accordingly, if the machine is being steered is judged by the signal of port P6.
OPERATION
1. While in NEUTRAL
The signals of the output ports (P1 - P4), travel signal (Port P5), and steering signal (Port P6) are not output.
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
2. While travelling straight
(The following drawing shows the circuit for traveling straight forward.)
While the left motor is operating for forward travel (the signal of port P2 is output) and the right motor is also operating for forward travel (the signal of port P4 is output), the pressures in left spring chamber (k) and right spring chamber (l) of steering signal valve (j) are set high. Accordingly, the steering signal valve is kept in neutral and the steering signal (Port P6) is not output.
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
12
3. When steered or pivot-turned
(The following drawing shows the circuit for left forward (slow) and right forward (fast) operation.)
If the operation quantities of both levers are different from each other as in the steering operation (If the difference of the pilot pressure between both sides is higher than a certain level), the pilot pressure is output as the steering signal.
In the case of the following drawing, the pressure in left spring chamber (k) of steering signal valve (j) is P2. The pressure in right spring chamber (l) is P4.
If (P4 - P2) x (Sectional area of spool) > Set spring load, the spool is changed to the direction of the arrow and the higher one of both PPC output pressures (the pressure of port P4 in this drawing) is output as the steering signal to port P6.
STRUCTURE AND FUNCTION TRAVEL PPC VALVE
12
4. When pivot-turned
(The following drawing shows the circuit for left reverse and right forward operation.)
While the left motor is operating for reverse travel (the signal of port P1 is output) and the right motor is operating for forward travel (the signal of port P4 is output), only the pressure in right spring chamber (l) of steering signal valve (j) is set high. Accordingly, the steering signal valve moves to the left and outputs the steering signal (port P6).