Hyundai HL955 Manual page 479

(1) Upstroking
1
2 4
LS pressure oil
System pressure oil
Return oil
1 Drive shaft
2 Swash plate
4 Counter piston
6 Counter spring
10 Control piston
12 Pressure compensator spool
Upstroking of the pump occurs as flow demand from loader and steering system.
The increased flow demand causes a LS pressure in LS line (19). The LS pressure in LS line (19)
combines with the force of spring (18) in cavity (20).
The force of spring (18) causes pump pressure to be higher than the LS pressure (19).
If the combination of LS pressure and of spring force is greater than the pump discharge pressure,
this difference pressure causes spool (13) to move right. As spool (13) moves right, the spool (13)
blocks the flow of supply oil to control piston (10). Pump swash plate (2) is controlled by pressure
and flow as much as hydraulic system requests.
When the oil flow to control piston (10) is blocked, the pilot oil in passage (22) drains to passage
(23). The oil then flows past pressure compensator spool (12) and through passage (16) into the
housing and via the drain line (14) to tank.
Supply oil flows through passage (15) to counter piston (4). The oil acts against counter piston (4).
The oil combines with the force of counter spring (6). This causes swash plate (2) to upstroke.
This also causes the pump flow to increase. As flow requirements are satisfied, the pump output
pressure increase. The pressure increases until the pressure in passage (15) moves flow
compensator spool (13) up to be satisfied with system requirement for pressure and flow.
·Pump discharge pressure = force of spring (18) + LS pressure (19)
14
6
15
10
16
17 18 19 20 13 23
13 Flow compensator spool
14 Case drain
15 Passage
16 Passage
17 Spring
18 Spring
6-15
LS pressure
12
21
22
L
L1
12
19 LS line from the metering pump
20 Cavity
21 Passage
22 Passage
23 Cavity
13
X
B
S
4 10
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