Hyundai Excavator R210LC-7. Service and repair manual - page 4

2-14

Overload preventive function

When the self pump delivery pressure P1 or the companion pump delivery pressure P2 rises, it
acts on the stepped part of the compensating piston(621). It presses the compensating
rod(623) to the right till the force of the outer spring(625) and inner spring(626) balances with
the hydraulic force. The movement of the compensating rod is transmitted to lever 1(612) via
pin(875).
Lever 1 rotates around the pin(875) (E) fixed to the casing(601).
Since the large hole section(F) of lever 1 contains a protruding pin(897) fixed to the feedback
lever(611), the feedback lever rotates around the fulcrum of point D as lever 1 rotates, and then
the spool(652) is shifted to the right. As the spool moves, the delivery pressure P1 is admitted
to the large diameter section of the servo piston via port CL, causes the servo piston move to
the right, reduces the pump delivery, flow rate, and prevents the prime mover from being
overloaded.
The movement of the servo piston is transmitted to the feedback lever via point D. Then the
feedback lever rotates around the fulcrum of point F and the spool is shifted to the left. The
spool moves till the opening between the spool(652) and sleeve(651) is closed.

621

651

652

623

612

601

625

626

B(E)
897

875

611

Small diameter
chamber

Servo piston

Large diameter
chamber

2-15

Flow reset function

As the self pump delivery pressure P1 or the companion pump delivery pressure P2 decreases,
the compensating rod(623) is pushed back by the action of the springs(625 & 626) to rotate
lever 1(612) around point E. Rotating of lever 1 causes the feedback lever(611) to rotate
around the fulcrum of point D and then the spool(652) to move to the left. As a result, port CL
opens a way to the tank port.
This causes the servo piston to move to the left and the pump's delivery rate to increase.
The movement of the servo piston is transmitted to the spool by the action of the feedback
mechanism to move it till the opening between the spool and sleeve is closed.

621

651

652

623

612

601

625

626

B(E)
897

875

Small diameter
chamber

Servo piston

Large diameter
chamber

2-16

Adjustment of outer spring

Adjust it by loosening the hexagon
nut(630) and by tightening(or
loosening) the adjusting screw C(628).
Tightening the screw shifts the control
chart to the right and increases the
input horsepower as shown in the
figure. Since turning the adjusting
screw C by N turns changes the setting
of the inner spring(626), return the
adjusting screw QI(925) by N A turns
at first.(A=2.2)

Adjusting values are shown in table

Low tilting angle(Low flow) command preferential function

As mentioned above, flow control and horsepower control tilting angle commands are
transmitted to the feedback lever and spool via the large-hole sections(C & F) of levers 1 and 2.
However, since sections C and F have the pins( 4) protruding from the large hole( 8), only the
lever lessening the tilting angle contacts the pin(897) ; the hole( 8) in the lever of a larger tilting
angle command is freed without contacting the pin(897). Such a mechanical selection method
permits preference of the lower tilting angle command of the flow control and horsepower control.

Adjustment of input horsepower

Since the regulator is of total cumulative horsepower type, adjust the adjusting screws of both
the front and rear pumps, when changing the horsepower set values. The pressure change
values by adjustment are based on two pumps pressurized at the same time, and the values will
be doubled when only one pump is loaded.

Delivery pressure, (P

)

Delivery flow

, Q

Adjustment of outer spring

Speed

Tightening

Compens- Input

torque

amount of ating control

change

adjusting starting amount
screw(C)

pressure

(924)

change
amount

(min

-1

)

(Turn)

(kgf/cm

)

(kgf m)

2100

+1/4

+15.9

+4.2

625

626

630

628

801

925

2-17

Adjustment of inner spring

Adjust it by loosening the hexagon nut
(801) and by tightening(or loosening)
the adjusting screw QI(925).
Tightening the screw increases the flow
and then the input horsepower as
shown in the figure.

Adjusting valves are shown in table

Adjustment of inner spring

Speed

Tightening

Compens- Input

torque

amount of ating control

change

adjusting starting amount

screw(QI)

pressure

(925)

change
amount

(min

-1

)

(Turn)

(kgf/cm

)

(kgf m)

2100

+1/4

+27.3

+4.1

Delivery pressure, (P

)

Delivery flow

, Q

626

801

925

2-18

Power shift control

The set horsepower valve is shifted by
varying the command current level of
the proportional pressure reducing valve
attached to the pump.
Only one proportional pressure reducing
valve is provided.
However, the secondary pressure Pf
(power shift pressure) is admitted to the
horsepower control section of each
pump regulator through the pump's
internal path to shift it to the same set
horsepower level.
This function permits arbitrary setting of the pump output power, thereby providing the optimum
power level according to the operating condition.
The power shift pressure Pf controls the set horsepower of the pump to a desired level, as
shown in the figure.
As the power shift pressure Pf rises, the compensating rod(623) moves to the right via the
pin(898) and compensating piston(621).
This decreases the pump tilting angle and then the set horsepower in the same way as
explained in the overload preventive function of the horsepower control. On the contrary, the
set horsepower rises as the power shift pressure Pf falls.

(3)

Delivery pressure, (P

)

Delivery flow

, Q

=MAX.

=MIN.

621

651

652

623

612

625

626

B(E)
897

875

898

611

Small diameter
chamber

Servo piston

Large diameter
chamber

2-19

Adjust it by loosening the hexagon
nut(808) and by tightening(or loosening)
the set screw(954).
The maximum flow only is adjusted
without changing other control
characteristics.

Adjustment of minimum flow

Adjust it by loosening the hexagon
nut(808) and by tightening(or loosening)
the hexagonal socket head set screw
(953). Similarly to the adjustment of the
maximum flow, other characteristics are
not changed.
However, remember that, if tightened too
much, the required horsepower during
the maximum delivery pressure(or
during relieving) may increase.

Adjustment of maximum and minimum flows

(4)

Adjustment of min flow

Speed

(min

-1

)

2100

Tightening

amount of

adjusting screw

(953)

(Turn)

+1/4

Flow change

amount

( /min)

+4.8

Delivery pressure, P

Delivery flow

, Q

808

954

806

953

Adjustment of min flow

Speed

(min

-1

)

2100

Tightening

amount of

adjusting screw

(954)

(Turn)

+1/4

Flow change

amount

( /min)

+4.8

Delivery pressure, P

Delivery flow

, Q

2-20

The regulator regulates
the maximum delivery flow
by inputting the pilot
pressure Pm. Since this is
a 2-position control method,
the maximum delivery flow
may be switched in two
steps by turning on/off the
pilot pressure Pm.(The
maximum control flow
cannot be controlled in
intermediate level.)

Functional explanation

As shown in the figure, the pilot pressure
Pm switches the maximum flow in two
steps.
When the pilot pressure Pm is given, it is
admitted to the lefthand side of the
piston QMC(648). The piston QMC
moves the stopper(647) and pilot
piston(643) to the right, overcoming the
force of the pilot spring(646), thereby
reducing the delivery flow of the pump.
Since the adjusting screw QMC(642) is
provided with a flange, the piston QMC
stops upon contact with the flange, and
the position of the pilot piston at this time
determines the maximum flow of the
pump.

Adjustment of Qmax cut flow

Adjust it by loosening the hexagon
nut(801) and by tightening(or loosening)
the adjusting screw QMC(642).
Tightening the screw decreases the
Qmax cut flow as shown in the figure.

(5) Qmax cut control

Pilot pressure, P

Delivery flow

, Q

Pilot pressure, P

Delivery flow

, Q

647

648

723

642

801

438

801

924

641

730

643

708

644

645

646

728

GROUP 2 MAIN CONTROL V

STRUCTURE

2. HYDRAULIC CIRCUIT

2-25

3. FUNCTION

CONTROL IN NEUTRAL POSITION

XAtl

XAs

XAb2

XBtl

XBs

(PSP)

(XBp2)

103

S
SWING

B2
BOOM 2

A1
ARM 1

STRAIGHT

TRAVEL

TL
TRAVEL(L)

101

XBa1

(XBp1)

XAa1

XAtr

XAo

XAb1

XAa2

XBtr

XBo

XBb1

XAk

XBa2

TRAVEL(R)

OP
OPTION

B1
BOOM 1

BK
BUCKET

A2
ARM 2

XBk

102

SECTION A-A

SECTION B-B

2-26

XAa2

(XBp2)

611

Dr2

LCa2

NR2

NR1

(XBp1)

(Ck1)

XBa2

Dr2

NR2

R2(P2)

Dr3

PaL

PbL

Dr4

Dr6

Pns

SECTION G-G

2-27

The hydraulic fluid from the pump P1 flows into casing A(101) through the inlet port(P1), through the
center bypass(21) and the parallel path(22). The hydraulic fluid from the pump P2 flows into casing
B(102) through the inlet port(P2) through the center bypass(18) and the parallel path(6).
The hydraulic fluid from the pump P1 is directed to the tank through the center bypass(21), negative
control orifice(NR1), the return path(13) and the return port(R2). The hydraulic fluid from the pump
P2 also flows to the tank through the center bypass(18), negative control orifice(NR2), return path
(4) and return port(R2). The hydraulic fluid in paths (6) and (22) is blocked and cannot return to the
tank.
In case a control lever is operated, the hydraulic fluid from the pump P2 is supplied to the travel right
spool(301) from path(18) and to the spools: option(309), boom1(303), bucket(304) and arm2(306)
from path(6). Additionally, the hydraulic fluid from the pump P1 is supplied to the travel left spool
(310) from path(7) while the swing(305), boom2(307) and arm(302) spools are supplied from
path(22).

2-28

NEGATIVE CONTROL

General operation

(1)

303

611

The negative control signal pressure from the center bypass(18, 21) occurs in the following cases
and controls the discharge of the pump.
1. Neutral condition when no function is being actuated.
2. The pilot control lever is partially operated.

The hydraulic fluid of the pump P1(28) flows into the return passage(13) through the center bypass
(21), the path(3) and orifice(9)(Within the poppet(15)). The restriction caused by this orifice thereby
pressurizes path(3). This pressure is transferred as the negative control signal pressure Fl to the
pump P1 regulator through the negative control line(4). It controls the pump regulator so as to
decrease the discharge of the pump P1(28).

2-29

611

101

NR1

(XBp2)

Qmax

Qmin

FL1

The negative control relief valve(611) consists of poppet(15), spring(16) and casing(101). When
the hydraulic fluid in the center bypass increases to the level that the pressure in the path(3)
reaches the set pressure of the spring(16), the hydraulic fluid in the path(3) pushes open the poppet
(15) and escapes into the return path(13).
In the unloaded state, the hydraulic fluid of the pump P1(28) entirely flows to the tank through the
path(21), orifice(9) and the return path(13). Therefore the pressure FL in the path(3) becomes
maximum(FL1) because all the discharge is reduced by the orifice(9) which in turn destrokes the
pump P1(28) so as to minimize the tilting angle and consequent discharge of the pump P1(28).
(Qmin)

Content .. 2 3 4 5 ..