CLSS
CLSS
CLSS
• Hydraulic Systems
Hydrodynamic Systems
Hydrostatic Systems
1. Open-Centre System
2. Closed-Centre System
Open-Centre System
Closed-Centre System
• Graphic Symbols
Hydraulic Graphic Symbols are used in place of actual
component drawings because they are easier to read and
quick to draw. The symbols are of a standard recognized
worldwide.
Pumps
Motors
Actuators
Valves
• Hydraulic Pumps
Every hydraulic system uses one or more pumps to
pressurize the hydraulic fluid. The fluid under pressure, in
turn, performs work in the output section of the hydraulic
system. Thus, the pressurized fluid may be used to move
a piston in a cylinder or to turn the shaft of a hydraulic
motor.
Types of Pumps
Three types of pumps find use in hydraulic system:
Gear Pumps
Gear Pump
The teeth of one gear project outward, while the teeth of the
other gear project inward toward the center of the pump.
Vane Pumps
Piston Pumps
• Hydraulic Actuators
• A hydraulic actuator receives pressure energy and
converts it to mechanical force and motion.
• Hydraulic Motors
• Hydraulic motors convert hydraulic energy into
mechanical energy.
The main types of motors are gear, vane, and piston. They
can be unidirectional or reversible. (Most motors designed
for mobile equipment are reversible.)
Automatic clamping
Fan drives
Conveyor drives
• Cylinders
• A cylinder is a hydraulic actuator that is constructed of a
piston or plunger that operates in a cylindrical housing by
the action of liquid under pressure.
Single-Acting Cylinder.
Double-Acting Cylinder.
This cylinder must have ports at the head and rod ends.
Double-Acting Cylinder
• Valves
Pressure-Control Valves
Pressure level control will fall into families associated with the
function to be performed. We can divide these categories into
six basic families and several subfamilies.
Relief Valve
Counterbalance Valve
Reducing Valve
• Hydraulic Excavators
Introduction
The hydraulic excavators are the earth movers playing a
major role in the development of the infrastructure like
excavation, road construction, building construction,
granite mining, ore mining, coal mining etc. The hydraulic
Department of Mechanical Engineering
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Operating Principle
Mechanical energy is transmitted from the engine (prime
mover- electric motor or diesel engine) to hydraulic
energy by the pumps. The flow of the oil generated by the
pump is passed through the control valves to the output
devices such as hydraulic cylinders (which cause relative
movements of boom, arm and bucket with respect to each
other and to the upper structure) and hydraulic motors
(for swing of the upper structure with respect to the
undercarriage and travel of the equipment on the ground
and for the other auxiliary functions).
Excavator
Excavators are heavy equipment used in civil works and
surface mining. An excavator, also called a 360-degree
excavator or digger, sometimes abbreviated simply to a
360, is an engineering vehicle consisting of a backhoe and
cab mounted on a pivot (turntable is a more apt
description) atop an undercarriage with tracks or wheels.
The term excavator is sometimes used as a general term
for any piece of digging equipment.
1. Crawler Excavator
Applications:
2. Wheeled Excavator
Applications:
Regulations
• Nomenclature of hydraulic
excavator (crawler type)
10. Break out force: force exerted at the tip of the bucket
due to hydraulic thrust of the cylinder, which tends to
move the bucket against resistance.
• Applications of excavators
Canal excavation
Trench digging
Pipe laying
Land levelling
Well sinking
Dredging
Mining
Quarrying
Tunnelling
Wood handling
Scrap handling
CLSS
Features
CLSS stands for Closed Centre Load Sensing System and is
featured as follows:
Configuration
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
3. LS Valve
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
4. PC Valve
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
5. Control Valve
(courtesy L&T-Komatsu)
Since one spool of this control valve is used for one work
equipment unit, the structure is simple.
Spool Valve
Unload Valve
1. When the control valve is neutral
FUNCTION
• When the control valve is neutral, the delivery Q equivalent
to the pump minimum swash plate angle is released to the tank
circuit. At the time, pump discharge pressure PP is set to 2.45
MPa {25.0kg/cm2} with spring (3) inside the vale. (The LS
pressure PLS is 0 MPa {0kg/cm2}.)
(Courtesy L&T-Komatsu)
1. Unload Valve PLS: LS
circuit (pressure)
2. Sleeve PP:
Pump circuit (pressure)
3. Spring T: Tank
circuit
4. Spool
OPERATION
• Pump discharge pressure PP is applied to the left end face of
spool (4) and LS pressure PLS is applied to the right end face.
• Since the LS pressure PLS is 0 when the control valve is
neutral, pump discharge pressure PP is only applied and is set
with the lead to spring (3).
• When pump discharge pressure PP rises to spring (3) load
(2.45 MPa {25.0 kg/cm2}), spool (4) will move toward the right
side and pump circuit PP will interconnect to tank circuit T
through the drill hole.
• Therefore, pump discharge pressure PP is set to 2.45 MPa
{25.0 kg/cm2}.
(Courtesy L&T-Komatsu)
1. Unload Valve PLS: LS
circuit (pressure)
2. Sleeve PP: Pump
circuit (pressure)
3. Spring T: Tank
circuit
4. Spool
OPERATION
• When the control valve is operated in the fine control mode,
LS pressure PLS will occur and will be applied to the right end
face of spool (4). At the time differential pressure between LS
pressure PLS and pump discharge pressure PP increases
because the opening area of the control valve spool is small.
• When the differential pressure between pump discharge
pressure PP and LS pressure PLS comes to spring (3) load
(2.45 MPa {25.0 kg/ cm2}), spool (4) will move to the right side
and pump circuit PP will interconnect to tank circuit T.
• This means that pump discharge pressure PP is set to the
spring force (2.45 MPa {25.0 kg/cm2} + LS pressure PLS, and
(Courtesy L&T-Komatsu)
1. Unload Valve PLS: LS
circuit (pressure)
2. Sleeve PP:
Pump circuit (pressure)
3. Spring T: Tank
circuit
4. Spool
OPERATION
• When the control valve is operated with large stroke, LS
pressure PLS will occur and will be applied to the right end face
of spool (4). At the time, the opening areas of the control valve
spool are large and the difference between LS pressure PLS
and pump discharge pressure PP is small.
Department of Mechanical Engineering
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Travel Valve
(Courtesy L&T-Komatsu)
OPERATION
• When spool (1) is operated, the pump discharge pressure PP
will be led to actuator circuit A through bridge passage b from
flow control valve (2) and spool notch a.
• At the same time, the actuator circuit pressure PA moves
pressure reducing valve (3) to the right side, and notches c and
d interconnect to the travel junction circuit e and LS circuit PLS
respectively.
(courtesy L&T-Komatsu)
T: To hydraulic tank
(courtesy L&T-Komatsu)
1. Screw 8.
Valve(pressure reducing valve)
2. Poppet 9. Spring
(safety valve)
7. PPC Valve
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
1. Spool 6. Nut
(for linking the lever)
4. Piston 9.
Retainer
5. Disk 10.
Body
(courtesy L&T-Komatsu)
Operation
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)
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
4) At full stroke
When disc (5) pushes down piston (4), and retainer (9) pushes
down spool (1), fine control hole f is shut off from drain
chamber D, and is connected with 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, and pushes the control valve spool. The oil returning from
chamber B passes from port P2 through fine control hole f' and
flows to drain chamber D. (Fig. 4)
(courtesy L&T-Komatsu)
8. Engine Control
(courtesy L&T-Komatsu)
1. Starting switch
2. Fuel control dial
3. Governor motor
4. Starting motor
5. Linkage
6. Battery relay
7. Battery
8. Engine throttle and pump controller
9. Fuel injection pump
(courtesy L&T-Komatsu)
Engine speed control
• The fuel control dial sends a signal to the engine throttle and
pump controller according to the position of the dial. The
engine throttle and pump controller calculates the angle of the
governor motor according to this signal, and sends a signal to
drive the governor motor so that it is at that angle. When this
happens, the operating angle of the governor motor is detected
by the potentiometer, and feedback is sent to the engine
throttle and pump controller, so that it can observe the
operation of the governor motor.
(courtesy L&T-Komatsu)
Stopping engine
(courtesy L&T-Komatsu)
FUNCTION
• The fuel control dial is installed under the monitor panel, and
a potentiometer is installed under the knob. The potentiometer
shaft is turned by turning the knob.
(courtesy L&T-Komatsu)
• As the potentiometer shaft is turned, the resistance of the
variable resistor in the potentiometer changes and a throttle
signal is sent to the engine throttle and pump controller. The
hatched area in the graph shown at right is the abnormality
detection area.
Governor Motor
(courtesy L&T-Komatsu)
1. Potentiometer
2. Cover
3. Shaft
4. Dust seal
5. Bearing
6. Motor
7. Gear
8. Connector
OPERATION
While motor is stopped
• Electric power is applied to both phases A and B of the motor.
FUNCTION
• The motor is turned according to the drive signal from the
engine throttle and pump controller to control the governor
lever of the fuel injection pump.
This motor used as the motive power source is a stepping
motor.
• A potentiometer for feedback is installed to monitor the
operation of the motor.
• Revolution of the motor is transmitted.
(courtesy L&T-Komatsu)
Engine and Pump Control Function
FUNCTION
• This function is for selecting any of the four working modes
"A," "B", "E" and "L" with the working mode selector switch on
the monitor panel. The controller can select optimum engine
torques or pump absorption torques for works to be expected.
(courtesy L&T-Komatsu)
• The controller detects the engine governor speed set with the
fuel control dial depending on the pump absorption torque set
in each mode and detects actual engine speeds. Then, the
controller controls all torques at each output point of the
engine so that the pump can absorb them.
(courtesy L&T-Komatsu)
• When an engine speed was lowered, the controller prevents
the engine from stopping by throttling the pump absorption
toque.
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
Mode E/ Mode B/ Mode L
Mode E B L
Partial Output
Point 90% 90% 55%
Model PC-130-7
Mode E 58.8 kW/2,000 rpm
{78.9 HP/2,000 rpm}
Mode B 58.8 kW/2,000 rpm
{78.9 HP/2,000 rpm}
Mode L 36.8 kW/1,500 rpm
{70 HP/1,500 rpm}
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
(courtesy L&T-Komatsu)
FUNCTION
• The machine is matched to various types of work properly
with the 2-stage relief function to increase the digging force,
etc.
1) Cut-off function
• When the cut-off function is turned on, the PC-EPC current is
increased to near the maximum value. By this operation, the
flow rate in the relief state is lowered to reduce fuel
consumption.
• Operating condition for turning on cut-off function.
Condition- The average value of the front and rear pressure
sensors is above 27.9 MPa {285 kg/cm2} and the one-touch
power maximizing function is not turned on.
The cut-off function does not work, however, while the machine
is travelling in mode A, the lock switch is turned on.
(courtesy L&T-Komatsu)
FUNCTION
Department of Mechanical Engineering
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4. AUTO-DECELERATION FUNCTION
FUNCTION
• If the all control levers are set in NEUTRAL while waiting for a
dump truck or work, the engine speed is lowered to the
medium level automatically to reduce the fuel consumption and
noise.
• If any lever is operated, the engine speed rises to the set
level instantly.
OPERATION
When control levers are set in neutral
• If all the control levers are set in NEUTRAL while the engine
speed is above the decelerator operation level (about 1,400
rpm), the engine speed lowers instantly to the first deceleration
level about 100 rpm lower than the set speed.
• If 4 more seconds pass, the engine speed lowers to the
second deceleration level (about 1,400 rpm) and keeps at that
level until any lever is operated again.
When any control lever is operated
• If any control lever is operated while the engine speed is kept
at the second deceleration level, the engine speed rises
instantly.
(courtesy L&T-Komatsu)