El oro como imagen literaria en The Gilded Age. A Tale of Today

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Electronic Brake Control Valve

The electronic brake control valve (1) is mounted to the top of the main case, situated below the operator seat. The brake control valve may be accessed by removing the operator seat, the seat pedestal, and the rear floor plate in the operator compartment.

The brake valve body contains a proportional solenoid valve (2) which is controlled by a signal from a PWM rotary position sensor connected to the service brake pedal. The solenoid is normally energized when the brakes are released. Depressing the service brake pedal DECREASES the amount of current to the solenoid and de-energizes it to apply the brakes.

The secondary brake valve is controlled by an ON/OFF solenoid (3). The ON/OFF solenoid is ENERGIZED by the secondary brake switch. The brake switch is a part of the service brake pedal and it is activated near the end of travel of the service brake pedal.

An ON/OFF solenoid also controls the parking brake valve (4). The parking brake valve solenoid is energized when the operator activates the parking brake switch.

1 2

3 5

The status of all three brake solenoids may be viewed through the Advisor panel (Power Train System Status screens) or through Cat ET. (The proportional service brake solenoid is

designated as the "left brake" on the Advisor status screen and in Cat ET.)

Brake pressure (B) at the brake control valve may be tested at the remote brake pressure port (5), located below the rear of the fuel tank.

NOTE: The following information outlines the state of the three brake valve solenoids in the three possible conditions:

Service Brakes Released

- Proportional brake valve solenoid - ENERGIZED - Parking Brake valve solenoid - DE-ENERGIZED - Secondary brake valve solenoid - DE-ENERGIZED

Service Brakes Applied (full)

- Proportional brake valve solenoid - DE-ENERGIZED - Parking Brake valve solenoid - DE-ENERGIZED - Secondary brake valve solenoid - ENERGIZED

Parking Brake Applied

- Proportional brake valve solenoid - DE-ENERGIZED - Parking Brake valve solenoid - ENERGIZED

- Secondary brake valve solenoid - ENERGIZED

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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 allows pump 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 the brakes 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 then decreases 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 the pressure 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.

Supply Oil from Pump Proportional

As the pilot pressure at the left end of the shutoff spool decreases, the pilot pressure at the right end of the shutoff spool moves the spool to the left, against the spring. When the spool moves all the way to the left, the holes in the spool are opened to drain due to the slot that is machined in the shutoff valve. The pressures in the accumulator chamber and the parking/secondary brake valve pilot chamber are now allowed to drain through the holes in the spool. As the pilot

pressure decreases, the spring begins to move the shutoff spool back to the right.

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, allowing the 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 again at 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, the Belville 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 and the 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 brake solenoid. 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.

NOTE: There are no longer any check valves installed in the brake valve body between the reducing spools and the secondary or parking brake valves. These check valves serve no purpose in differential steer machines. These check valves are present,

however, in brake valves used on Finger Tip Control machines. They serve to isolate the left brake and right brake passages from each other, for steering purposes.

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The illustration above, and those on the next two pages show the electronic brake valve as if it had been sliced in half, horizontally, with the upper half laid over to the right. The lines in the illustration represent the internal passages of the brake valve as they would normally be connected.

Illustration 79 shows the electronic brake valve with the brakes released. When the operator releases the service brake pedal, the PWM rotary position sensor (connected to the brake pedal) sends a signal to the Power Train ECM. The Power Train ECM then increases the current to the (proportional) brake solenoid. The amount of current sent to the solenoid is directly

proportional to the position of the service brake pedal.

The increased current to the solenoid closes the poppet in the solenoid valve which closes off the flow of pump supply oil to drain. The result is increased pilot pressure to both pressure

reducing spools. This increased pressure moves the reducing spools downward. As the spools move downward, the flow of supply oil is shut off to the drain passage and the supply oil then flows into the brake passage and out to the brakes. This increased pressure releases the brakes against the brake (Belville) springs.

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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 (connected to 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 brakes is 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 the pilot 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.

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