manual del estudiante d8t - 12

8/12/2019 Manual Del Estudiante D8T - 12

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SISTEMA HIDRULICO DE LA TRANSMISIN

The three-section fixed displacement power train oil pump is mounted to the right front of

the main case and is driven by a drive shaft connected to the rear of the implement pump.

The transmission charging (C) section of the power train oil pump provides high pressureoil to the transmission main relief valve, which maintains a common top pressure for

operation of the transmission modulating valves and the brakes.With the common top pressure power train strategy, transmission clutch engagement

pressure calibrations and brake pressure adjustments no longer need to be performed.

(Clutch fill time calibrations and brake touch-up calibrations are still required.) When the

transmission main relief valve is properly adjusted, all of the pressures for the transmissionclutches and for the brakes are also properly adjusted.

The torque converter charging (B) section of the power train oil pump supplies oil to thetorque converter, through the priority valve. Oil from the transmission charging section that

flows past the main relief valve mixes with the lube oil from the power train oil cooler and

is used to lubricate and cool the transmission and the bevel gears.

The scavenge (A) section of the power train oil pump draws oil from the transmission and

bevel gear case and from the torque divider housing and directs it to the sump in the maincase.


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VLVULA DE PRIORIDAD

The illustration above shows the priority valve operating in the Priority Mode. The priority

valve operates in the Priority Mode under the following conditions:

- power train oil (main sump) temperature less than 40C (104F)

- engine speed below 1300 rpm- during transmission speed or directional changes

During operation in the Priority Mode, the solenoid coil of the priority valve is DE-

ENERGIZED. The solenoid valve then blocks torque converter charge oil from entering thespool cavity and allows the oil from the spool cavity to drain to tank. With only tank

pressure at the left end of the spool, the spring shifts the spool back to the left. With the

spool shifted to the left, only a small amount of torque converter charge oil can flow intothe passage going to the torque converter inlet relief valve. With the passage to the torque

converter mostly blocked, the pressure of the torque converter charge oil increases until it

overcomes the combined force of the check valve spring and the pressure of the oil fromthe transmission charging section of the power train oil pump. As a result, the check valve

opens and the flow of torque converter oil mixes with the transmission and brake oil. This

ensures that there is enough oil to safely operate the transmission and brakes.

The priority valve will default to Normal Mode when the parking brake is activated.


3/14

VLVULA MODULADORA DE LA TRANSMISIN

The transmission clutches are hydraulically engaged and spring released. The transmission

modulating valve solenoids are energized to send transmission charge oil to the clutches, as

shown in the illustration above. As current is applied to the solenoid, the pin extends to the

right and moves the ball closer to the orifice. The ball begins to restrict the amount of oil todrain through the orifice. This restriction causes the pressure to increase at the left end of

the valve spool. As the pressure at the left end of the valve spool increases, the spool shiftsto the right, closing off the passage from the clutch to the drain. At the same time, the

movement of the valve spool to the right opens the passage from the pump supply to the

clutch. This causes the clutch pressure to increase.

De-energizing the solenoid decreases the force of the pin against the ball. This decreased

forc allows the pressure at the left end of the valve spool to unseat the ball, de-pressurizing

the chamber at the left end of the spool. With no pressure at the left end of the spool, thevalve spool shifts to the left due to the spring force plus the supply oil pressure. This

condition reduces the pressure to the clutch by closing off the supply passage to the clutch

and opening up the drain passage. When the pressure to the clutch falls below the clutchengagement pressure, the clutches will be released by spring force.

When the transmission is in FIRST SPEED FORWARD, the modulating valves that control

flow to the No. 2 and the No. 5 clutches receive a signal from the Power Train ECM. Thissignal energizes the solenoid which sends flow to engage the clutches.


4/14

The proportional solenoid valve for the service brakes is controlled by the Power Train

ECM.The solenoid valve is ENERGIZED to release the brakes. The Power Train ECM

determines the amount of current to the solenoid by the position of the service brake pedal.

When the proportional solenoid (valve) is energized, the pilot valve is closed. This allowspump supply oil to pressurize the pilot pressure chambers at the proportional solenoid

valve, the parking brake valve and the secondary brake valve, and in the accumulator

chamber. As the accumulator chamber pressure increases, the reducing spool moves to the

right against the spring, closing off the drain passage. At the same time, the passage to thebrakes is opened to the passage from the pump supply oil. Pressure then builds in the

pressure feedback chamber and the passage to the brakes. As the pressure increases, the

spring applied brakes are released.

When the operator depresses the service brake pedal, the PWM sensor attached to the

service brake pedal sends a signal to the Power Train ECM. The Power Train ECM thendecreases the current to the proportional solenoid at a rate that is directly proportional to the

movement of the pedal. As the solenoid is DE-ENERGIZED, the pilot valve opens and

allows the pump supply oil in the pilot pressure chamber to drain to tank. This reduces thepressure in the pilot pressure chamber at the solenoid valve. The accumulator chamber and

the parking/secondary brake valve pilot chamber are also reduced by draining through the

holes in the shutoff spool.


5/14

As the shutoff spool moves back to the right, the holes in the spool are covered again by the

right end of the shutoff valve. This reduces the rate of reduction in pilot pressure, allowingthe brakes to be slowly applied. The pilot oil can then only escape by flowing between the

outer diameter of the shutoff spool and the inner diameter of the shutoff valve, and then

through the holes in the shutoff spool. As the pilot pressure slowly decreases, the spring

moves the shutoff spool further to the right until the holes in the spool are uncovered againat the right end of the shutoff valve. The remainder of the pilot pressure then completely

drains to tank through the shutoff spool.

As the pilot pressure decreases, the combined force of the reducing spool spring and the

pressure in the feedback chamber moves the reducing spool to the left. The accumulator

piston acts as a cushion and aids in preventing the reducing spool from moving too rapidly.As the reducing spool moves to the left, the pump oil supply passage to the reducing spool

is closed off. At the same time, the tank passage to the reducing spool is opened, allowing

the pressure oil in the brakes to drain to tank. As the pressure to the brakes decreases, theBelville springs begin to engage the brakes.

If the operator depresses the service brake pedal completely, the secondary brake switch is

activated. The secondary brake switch makes a direct connection between the battery andthe secondary brake valve solenoid, which ENERGIZES the secondary brake solenoid.

Also, when the parking brake switch is set to the ON position, the parking brake valve

solenoid is connected directly to the battery, which ENERGIZES the parking brakesolenoid. As a backup measure, the secondary brake solenoid is also ENERGIZED when

the parking brake switch is set to the ON position.

Energizing either the parking brake or the secondary brake solenoids completely drains all

pilot pressure oil, resulting in all the oil being drained from the brakes, resulting in full

engagement of the brakes.


6/14

Illustration 80 shows the electronic brake valve when the brakes are fully engaged. When

the operator depresses the service brake pedal, the PWM rotary position sensor (connectedto the pedal) sends a signal to the Power Train ECM. The Power Train ECM then decreases

the current to the proportional (service) brake solenoid. The amount of current sent to the

solenoid is directly proportional to the position of the service brake pedal.The decreased current to the solenoid opens the poppet in the solenoid valve and opens the

flow of pump supply oil to drain. The result is decreased pilot pressure to both pressure

reducing spools. This decreased pressure allows the springs below the reducing spools to

move the reducing spools upward. As the spools move upward, the passage from the brakesis connected to the drain passage, which decreases the pressure to the brakes. This

decreased pressure allows the brake (Belville) springs to begin engaging the brakes.

When the operator completely depresses the service brake pedal, the secondary brake

switch is activated. The secondary brake switch then connects the battery to the secondary

brake solenoid. The ENERGIZED secondary brake solenoid valve completely dumps thepilot pressure to tank, which causes the reducing spools to move upward. As the spools

move upward, the passage from the brakes is connected to the drain passage, which

decreases the pressure to the brakes and the brakes are fully engaged.


7/14

The steering system for the D8T Track-type Tractor has been upgraded to an electronically

controlled differential steering system. These upgrades include:

- solenoid controlled over-center bi-directional piston pump

- steering control lever using three rotary position sensors (triple redundant signal)- bent axis steering motor with speed and direction sensor

- steering system controlled by the power train ECM

Shown above is a schematic of the steering hydraulic system for the D8T in the NO TURN(NO STEER) condition. The gear-type charge pump and the over-center bi-directional

steering pump operate similar to the steering pump on the current D8R Series II Track-type

Tractor, except that the steering pump is controlled by two solenoid valves. (The D8RSeries II used a pilot operated pump control valve to control the steering pump.) Also, the

D8T steering control lever (tiller) uses three rotary position sensors to send a signal to the

pump control solenoid valves through the Power Train ECM, instead of the mechanicallyoperated pilot valve used in the D8R Series II machine. The steering motor is similar to that

used on the current D8R Series II, but now it utilizes a dual Hall Effect sensor in order to

provide speed and direction output information to the Power Train ECM.


8/14

Steering System Components

Charge pump: The charge pump fills the system with oil during start-up and provides oilfor the drive loops and pilot oil for the steering control valve. Charge pressure is maintained

by the charge pressure relief valve and is set to approximately 2930 kPa (425 psi) at high

idle. (On machines equipped with dual tilt, charge oil is also used as pilot oil for theoperation of the dual tilt valve.)

Pressure override (cutoff) valve: When the pressure in either side of the steering loopreaches approximately 40160 kPa (5825 psi), the pressure override (POR) valve opens and

destrokes the pump by draining the charge pressure sent to the steering control valve, which

is used to move the pump actuator piston.

Charge pressure relief valve: The charge pressure relief valve limits the charge pressureto approximately 2850 kPa (413 psi) at 2000 rpm. Charge oil is then sent to the drive loop,the steering control valve, and the pump actuator piston.

Crossover relief and makeup valves: Each side of the drive loop has a crossover reliefand makeup valve that limits the pressure spikes in either side of the drive loop. Thesevalves also direct the charge pressure through an internal check valve that opens to fill the

low pressure side of the drive loop.

Pump control spool and pump actuator piston: The steering pump control spool iscontained in the pump control valve. The pump control spool is moved by the pump control

solenoids. The pump control spool directs charge pressure to the left or to the right end ofthe pump actuator piston. As the pump actuator piston moves, it changes the angle and/or

direction of the swashplate. The feedback lever in the pump control valve follows up to

move the pump control spool back against the pump control solenoid. This ensures that thecorrect pressure is metered to the pump actuator piston for the amount of steering flow

requested. In the NEUTRAL (or NO STEER) position, reduced charge pressure is present

at each end of the pump actuator piston.

Steering lever position sensors: Three (triple redundant) PWM rotary position sensors areattached to the shaft of the steering control lever (tiller). The position sensors send PWM

signals to the Power Train ECM. The PWM signals reflect the position of the steering tiller.The Power Train ECM then sends current to either the left or the right steering pump

control solenoid, which moves the pump control spool.

Steering pump control solenoids: The steering pump control solenoids (left and right) areinstalled in the steering control valve and are energized by the Power Train ECM. The

Power Train ECM determines the amount of current and which pump control solenoid to

energize based on the signals received from the steering lever position sensors. As the

solenoids are energized, the solenoid pin pushes against the end of the pump control spool


9/14

SISTEMA DE IMPLEMENTOS

MULTIPLE PILOTO

The pilot manifold is mounted to the end cover on the valve stack. It supplies pilot oil to the

solenoid valves that are located on either end of each implement control valve. The pilotmanifold is supplied with oil from the implement pump, through the inlet manifold, the

valve stack, and then the end cover. The pilot manifold contains the implement pump

pressure sensor, the pressure reducing valve, the Hydraulic Pilot Accumulator Pressure

(HPAP) test port, and the Hydraulic Pilot Supply (HPS) pressure test port.

As the oil enters the pilot manifold, it passes through a screen before it reaches the pressure

reducing valve. The pressure reducing valve is infinitely variable, and meters the oil toprovide pilot oil pressure of approximately 3275 172 kPa (475 25 psi). After passing

through the pressure reducing valve, this oil becomes pilot oil.

The pilot oil then passes through the pilot filter. From the pilot filter, the pilot oil thenpasses through the accumulator check valve, where it is available to the accumulator and

the pilot relief valve.


10/14

The pilot relief valve limits the pressure past the pressure reducing valve to approximately

6500 kPa (940 psi). In the event of pressure spikes in the pilot system, this valve opens to

dissipate the excess pressure. The accumulator stores energy (pilot pressure) so that the

implements may be lowered in a dead engine situation.

A check valve is positioned upstream of the accumulator which prevents back-flow in the

system in case of low pressure conditions. The check valve also prevents the accumulatorfrom discharging when the machine is shut down.

From the accumulator, the pilot oil then flows to the implement lockout valve. Theimplement lockout valve is solenoid operated and is ENERGIZED, when in the

UNLOCKED condition.

The implement lockout valve is controlled by the implement lockout switch, located on theright console, in the operator compartment. When this valve is in the LOCKED condition,

or DE-ENERGIZED, the pilot oil is blocked and the implements cannot be moved with the

implement controls.

When the implement lockout valve is in the UNLOCKED condition, the pilot oil exits the

pilot manifold at the outlet and is directed through a passage in the end cover and thenthrough the pilot oil passages in the valve stack. Each implement valve then directs the pilot

oil to the solenoid valves located on either end of each implement control valve.

When the operator activates an implement, the appropriate solenoid valve directs the pilot

oil into the pilot chamber of the valve. The pilot pressure then shifts the implement valve

spool


11/14


12/14

This schematic shows the components and conditions in the implement system with the

engine started and all the implements in HOLD. Oil is drawn from the hydraulic tank by theload sensing variable displacement, piston-type implement pump. Supply oil is directed to

the closed-center control valves by the pump. Return oil from the control valves and pump

case drain oil are sent to the tank.

When a control lever is moved, oil from the implement control valve is directed to the

doubl acting implement cylinders.

The signal network line is in series with each control valve and passes through each valvebody.

The signal network terminates at the pump control valve. When an implement is activated,

a signal is generated by the work port load. This signal is sent through the signal network.A resolver network inside the implement valves consists of a series of resolver valves

which compare the signals from the implements and send the highest signal to the pump

control valve.The major components in this system are: the implement pump, the inlet manifold, the

blade lift and tilt control valves, the ripper lift and ripper tip control valves, the pressure

reducing valve, the solenoid controlled pilot valves, the implement cylinders, and the

quick-drop valve.

When the operator moves the dozer control lever from HOLD to RAISE, the dozer controllever sends a signal to the Implement ECM. The Implement ECM then sends a

corresponding current to the solenoid controlled blade lift pilot valve. The pilot valve opens

to send pilot oil into the pilot chamber, which moves the main valve spool to the RAISE

position. This allows high pressure pump supply oil to flow to the rod end of the blade liftcylinders and the blade raises.

As the blade raises, oil from the head end of the lift cylinders returns through the blade liftcontrol valve. It flows past the main valve spool and then back to the hydraulic tank.

At the same time, the pressure in the rod end of the lift cylinders is felt in the blade lift

control valve. That pressure, or load sensing signal, is transmitted through the signalresolver network back to the pump compensator valve. The pump compensator valve is set

to command the pump to upstroke and increase pump flow to meet the demand.


13/14

SISTEMA DEL VENTILADOR HIDRULICO

Standard on the D8T Track-type Tractor is the hydraulic demand fan. Although the fan is

part of the hydraulic system, it is controlled by the Engine ECM. The Engine ECMconsiders four inputs for controlling the fan. The hydraulic oil temperature sensor, the

engine intake air temperature sensor, and the engine coolant temperature sensor all providetemperatura information to the Engine ECM. The Engine ECM monitors all three of these

temperatura inputs. The highest temperature (relative to the percentage of its temperature

map) is the controlling temperature for fan speed. The fan pump discharge pressure sensor

is the fourth input to the Engine ECM. Fan pump discharge pressure is controlled by theEngine ECM to determine fan speed.

The Engine ECM monitors the temperature inputs and also considers fan pump dischargepressure to provide a signal to the (proportional) fan pump pressure control solenoid. When

the solenoid receives minimum current from the Engine ECM, maximum flow is sent to the

fan motor, causing the fan to turn at the maximum controlled rpm (about 1350 + 25 rpm),as shown above. Maximum mechanical pump pressure (high pressure cutoff - no current or

a failed solenoid) is set to approximately 15000 + 860 kPa (2175 + 125 psi). Maximum

pressure regulated by the Engine ECM software is approximately 13250 + 500 kPa (1922 +75 psi).


14/14

The standard hydraulic demand fan with the fan at minimum speed:

If maximum fan speed is not required, the fan pump pressure control solenoid is energized,

causing the fan to turn at a slower speed. Minimum fan speed is attained when the fan

pump pressure control solenoid is completely energized (approximately 450 + 50 rpm). Fan

pump pressure at minimum speed should be set to approximately 1827 240 kPa (265 35psi).

If communication is lost between the Engine ECM and the fan pump pressure control

solenoid, the fan will default to the maximum mechanical pressure setting, which isapproximately 15000 + 860 kPa (2175 + 125 psi). This results in a fan speed of

approximately1369 rpm (as set at the factory).

NOTE:If the engine is in the overspeed condition, the Engine ECM will regulate the

fan toward minimum pressure in an effort to protect the fan hydraulic system

manual del estudiante d8t - 12

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