SANY Crawler Hydraulic Excavator SY195C9, SY205C9, SY215C9, SY225C9. Service Manual

4-95

Structure and Function

4.6.6.1 Operation of components

Counterbalance valve

Function

●

When external load makes the rotating
speed of the piston motor faster than the
rated rotating speed of supplied delivery,
this valve controls the speed of the motor
and prevent over-speed of the motor in re-
lation with the supplied delivery.

●

The counterbalance valve and the relief
valve constitute the braking circuit. The
braking circuit applies braking force onto
the rotating motor and stops the motor
gradually.

●

This valve can serve as a shuttle valve
for high pressure selection to release the
brake under its own pressure.

●

The structure of a standard counterbalance
valve is shown as below. The following in-
formation describes the operating principle
of a standard counterbalance valve.

4-96

Structure and Function

●

When the main valve is neutralized (motor
stopped), port M1 and port M2 are shut off
by spool (1) and check valve (2) since no

pressure is generated at port P1 and port
P2. The motor is not rotating.

ZX215-1002094

6-2

7-2

5-2

4-2

2-2

2-1

4-1

5-1

7-1

6-1

8-2

8-1

Circuit B

Circuit C2

Damper chamber A2

Orifice D4

Spring chamber 2

Circuit C1

Orifice D1

Damper chamber A1

Orifice D2

Spring chamber 1

Orifice D3

A. Stopped state

4-97

Structure and Function

●

When hydraulic oil from the main pump
enters port P1 of the counterbalance valve,
spring (3) is pushed to the left by check
valve (2-1), opening circuit C1. The hy-
draulic oil enters the piston motor via port
M, trying to make the motor rotating. At the
same time, return oil from the piston motor
enters the counterbalance via port M2, but
it is stopped by check valve (2-2). The out-
put pressure of the main pump increases
as a result, and the hydraulic oil works
on the inside of spring chamber (1) and

damper chamber (A1) via ori

ce (4-1) and

check valve (5-1). The force generated in
this way pushes spring (7-2) on the other
side and moves piston (1) to the right. At
this time, return oil from port M2 passes
through circuit of the notch on the periph-
ery of piston (1), and through port P2 when
pressure is generated at port M2, and en-
ters the tank via the main valve

nally. The

motor is activated at this time.

ZX215-1002095

6-2

7-2

5-2

4-2

2-2

2-1

4-1

5-1

7-1

6-1

8-2

8-1

Circuit B

Circuit C2

Damper chamber A2

Orifice D4

Spring chamber 2

Circuit C1

Orifice D1

Damper chamber A1

Orifice D2

Spring chamber 1

Orifice D3

B. When the motor is activated

4-98

Structure and Function

●

When the engine runs at an excessively
high speed because of external force ap-
plied on it, the motor may lose control. At
this time, port P1 serves as the inlet side,
and the pressure drops. Pressure in spring
chamber 1 and damper chamber A1 also
drop. As a result, pison (1) moves to the
left under the force of spring (7-2), closing
circuit B. Circuit at the suction side is also
closed at the same time when the circuit
at return side is closed. When circuit B is
closed, pressure at port P1 rises due to
hydraulic oil from the main pump, moving
piston (10 to the right again. In this way,
when external load generates pump effect,
slight movement of piston (1) keep circuit
B open. The rotation speed of the motor
keeps in line with fuel supply of the main
pump, and the motor will not lose control
because of the vacuum in the hydraulic
system.

C. Counterbalance function

4-99

Structure and Function

●

The counterbalance valve and the relief
valve forms the braking circuit. When the
main valve is neutralized position, hydrau-
lic oil from the main pump is cut off, and
pressure at port P1 and P2 is the same.
As a result, piston (1) moves to the neutral
position, and the opening area of circuit B
decreases. At the same time, because of
the inertia of external force, the motor does
not stop rotating (pump effect), and pres-
sure at port M2 rises and serves as the

braking force of motor rotation. When the
pressure at port M2 reaches the set pres-
sure of relief valve (8), cone valve (8-1) at
port M1 overcomes the force of spring (8-
2) and moves to the left, and hydraulic oil

ows the port M1. In this way, the impact-

ing force due to inertia at port M2 is under
control, and vacuum at port M1 is avoided.

D. Braking of motor

ZX215-1002096

6-2

7-2

5-2

4-2

2-2

2-1

4-1

5-1

7-1

6-1

8-2

8-1

Circuit B

Circuit C2

Damper chamber A2

Orifice D4

Spring chamber 2

Circuit C1

Orifice D1

Damper chamber A1

Orifice D2

Spring chamber 1

Orifice D3

4-100

Structure and Function

●

The counterbalance valve can function
as a shuttle valve to release travel brake.
When hydraulic oil is fed to port P1, piston
(1) moves to the right, as shown in

g. 4.

At this time, drain circuit F of motor body
is cut off, and circuit D leading to cylinder
chamber E for travel braking is connected.
Hydraulic oil flows to circuit G via the ori-

ce, and enters travel brake cylinder cham-

ber E to release travel brake. In addition,
piston (1) moves to neutral position, as
shown in

g 5 when motor stops. Circuit D

is closed and drain circuit F of motor body
is connected. Hydraulic oil in travel brak-
ing cylinder chamber E is conducted to the
drain circuit of motor body, and travel brake
is applied.

ZX215-1002097

Circuit F

Circuit D

Circuit G

Circuit F

Cylinder chamber E

Orifice

ZX215-1002098

Circuit F

Circuit D

Circuit G

Circuit F

Cylinder chamber E

Orifice

E. Shuttle valve function for high pressure
selection

4-101

Structure and Function

Operation of parking brake

1) When travel begins

●

As the travel lever is operated, pressurized
oil from the pump activates counterbalance
valve spool (10), opens the parking brake
circuit, and flows to chamber A of brake
piston (12). Pressurized oil overcomes the
force of spring (11) and pushes piston (12)
toward the left.

●

Since the pushing force to plate (13) and
disc (14) disappears, plate (13) is sepa-
rated from disc (14) and the brake is re-
leased.

2) When travel stops

●

As the travel lever is placed in neutral,
counterbalance valve spool (10) returns to
the neutral position and closes the park-
ing brake circuit. The pressurized oil in
chamber (A) of brake piston (12) passes
through the ori

ce of the brake piston and

is drained to the motor case. Brake piston
(12) is pushed to the right by spring (12).
Plate (13) and disc (14) are pushed to-
gether, and the brake is applied. As brake
piston (12) returns,

ow of pressurized oil

is reduced with slow return valve (22). The
time delay will be set to activate the brake
only after the machine has stopped.

ZX215-1002099

Travel control valve

ZX215-1002100

Travel control valve

4-102

Structure and Function

Brake valve operation

●

The brake valve consists of suction safety
valve (8A) and counterbalance valve (18).
Functions and operations of respective
components are described below.

1) Counterbalance valve and check valve

Function

●

When the machine is travels downhill, the
weight of the machine tends to make the
travel speed faster than the motor speed.
If the machine travels with the engine at
low speed, the motor may rotate at zero
load, resulting in run away and inviting a
very dangerous situation. These valves are
used to avoid such a situation by control-
ling the machine to travel as per the engine
speed (pump delivery).

Operation when pressurized oil is supplied

●

Operating the travel lever conducts the
pressurized oil from the control valve to
port (PA). The pressurized oil opens suc-
tion safety valve (8A) and then flows to
motor outlet port (MB) via motor inlet port
(MA). The motor outlet side is closed by
suction safety valve (8B) and spool (19),
so the pressure at the supply side rises.

ZX215-1002101

Travel control valve

ZX215-1002102

Travel control valve

4-103

Structure and Function

Operation of brake during downhill travel

●

If the machine goes out of control while
travelling downhill, the motor will be caused
to rotate without load to decrease the inlet
side oil pressure. Pressure in chamber (S1)
is released via orifices (E1) and (E2). As
the pressure in chamber (S1) goes below
the spool selector pressure, spool (19)
is returned to the left by spring (20) and
outlet port (MB) is throttled. The pressure
at the outlet port side rises, generating ro-
tation resistance on the motor to prevent
the machine from losing control. On the
other hand, the spool moves to a position
where the pressure on outlet port (MB) can
be balanced against the machine's own
weight and the inlet port pressure. Oil

from the outlet circuit is reduced to ensure
the travel speed corresponded to the pump
delivery.

●

The pressurized oil on the supply side

ows to chamber (S1) via ori

ce (E1) and

ori

ce (E2) of the spool (19). As the pres-

sure in chamber (S1) goes above the spool
selector pressure, spool (19) is pushed
toward the right. Port (MB) and port (PB)
are connected, the motor outlet port side
opens and the motor starts rotating.

ZX215-1002103

E1 E2

Travel control valve

ZX215-1002104

Travel control valve

4-104

Structure and Function

2) Safety valve

Function

●

When the machine travel is stopped (or it
is travelling downhill), the counterbalance
valve closes the inlet and outlet circuits of
the motor. Since the motor is rotated by
inertial force, pressure in the motor outlet
port side is abnormally increased, poten-
tially resulting in damages on the motor
and piping. The safety valve releases this
abnormal pressure to the inlet port side of
the motor in order to prevent damages to
the equipment.

Operation

1. When travel is stopped (or when travelling

downhill) (Right swing)

●

Reduction of the pressure at motor inlet
(PA) decreases the pressure in chamber
(S1). When it drops beyond the spool
switching pressure, the spool is returned to
the left by spring (20), reducing the pres-
sure at outlet passage (B1). At this time,
the motor continues rotating due to its iner-
tial force, thus pressure on the outlet port
(MB) is increased.

●

When the pressure rises above the set
pressure of the suction safety valve (8A),
the poppet opens. The pressurized oil
passes through notch (A1) of spool (19)
into chamber (MA) of the circuit at the op-
posite side.

ZX215-1002105

Travel control valve

ZX215-1002107

Spool

4-105

Structure and Function

2. When starting travel (or when traveling at a

constant speed)

●

As the travel lever is operated, the pres-
surized oil from the pump moves spool (19)
toward right. The passage to the suction
safety valve functions as a circuit which
passes through notch (B2) of spool (19),
producing large differential pressure. The
pump pressure rises, providing a large
tractional force to the valve.

3) Relief valve

●

The structure of the relief valve is shown
in the right figure. This valve is area dif-
ference and direct

ow type. It has impact

damping function during starting and brak-
ing.

ZX215-1002106

Travel control valve

ZX215-1002108

A. Operation principle and function

●

When the main valve makes the motor
to start or brake, front pressure of cone
valve (2-9-2) rises above the set pressure
and the force of spring (2-9-5), and moves
cone valve (2-9-2) to the right and off the
valve seat. Pressurized oil in the front of
cone valve (2-9-2) is bypassed to the low
pressure side. The impact due to inertia
energy at the high pressure side is put un-
der control and vacuum is prevented from
occurring at the low pressure side through
bypassing pressurized oil to the low pres-
sure side.

ZX215-1002109

2-9-3

2-9-2

2-9-5

4-106

Structure and Function

ZX215-1002110

2-9-3

2-9-9

2-9-2

2-9-5

Area S2

Area S1

Spring chamber D

B. Damping function

●

When the relief valve begins to function,
damping piston (2-9-9) moves to the left.
As a result, low pressure is maintained in
spring chamber D. At this time, the loaded
area of cone valve (2-9-2) is S1, and it is
much larger than the normal set loaded
area S1-S2 of the relief valve. So, when
damping piston (2-9-9) is moving, the func-
tional pressure of relief valve is maintained
at 1/3 of normal set pressure in order to
absorb the impact at the high pressure
circuit side due to inertia energy. When
the movement of damping piston stops,
pressure in spring chamber D rises. Pres-
sure at both side of cone valve (2-9-2) is
the same, and the relief valve is working at
normal set pressure. In this way, the relief
valve reduces the impact during motor start
and brake by a two-stage action to provide
excellent performance.

ZX215-1002111

Pressure

Time

Damping method

4-107

Structure and Function

4.6.7 Valve control system

ZX215-1002112

4-108

Structure and Function

Travel PPC valve

L. travel control lever

R. travel control lever

Right PPC valve

Right joystick

Accumulator

Transition block

Hydraulic pump

Main control valve

10. Solenoid valve
11. Left joystick
12. Left PPC valve

(1) HOLD
(2) Boom UP
(3) Boom DOWN
(4) Bucket DUMP
(5) Bucket DIG
(6) HOLD
(7) Arm IN
(8) Arm OUT
(9) Right swing
(10) Left swing
(11) Neutral
(12) Reverse travel
(13) Forward travel

Control lever position

4-109

Structure and Function

4.6.8 Pilot valve

4.6.8.1 Work equipment and swing pilot valve

ZX215-1002113

64~73.5Nm

19~22Nm

From pilot pump relief valve

P1:

L.H. Pilot valve: Arm OUT

R.H. Pilot valve: Boom DOWN

P2:

L.H. Pilot valve: Arm IN

R.H. Pilot valve: Boom UP

P3:

L.H. Pilot valve: Swing LEFT

R.H Pilot valve: Bucket DIG

P4:

L.H. Pilot valve: Swing RIGHT

R.H. Pilot valve: Bucket DUMP

T: To

tank

4-110

Structure and Function

Plunger

Metering

spring

Centering

spring

Piston

Disc

Nut (for lever connection)

Joint

Plate

Retainer

10) Valve body

ZX215-1002114

A-A

SANY Crawler Hydraulic Excavator SY195C9, SY205C9, SY215C9, SY225C9. Service Manual - page 12