Hydraulic System
Location of Components
(1) Cooling and test manifold. (2) Steer pump. (3) Pressure switch. (4) Brake valve. (5) Brake switch. (6) Fixed disc. (7) Brake caliper.
The secondary/parking brake is used routinely to hold a stopped or parked machine in place. It is also used in an emergency to stop the machine if the primary service brake falls.
The braking systems have been designed and tested to be in accordance with SAE J1136 braking recommendations.
The hydrostatic propel system serves as the primary service brake normally used to stop the machine. The primary service brake operates when the propel lever is moved to to STOP position. This creates hydrostatic braking, which stops the machine.
Reference: For information on the hydrostatic propel system, see Propel Systems Operation Testing and Adjusting, Form No. KEBR2373.
Fixed Disc (6) and Brake Caliper (7)
Fixed disc (6) and brake caliper (7) are mounted on the right side of the vibratory drum. Brake caliper (7) is spring-applied and hydraulically released. Fixed disc (6) is secured to the drum support. When the brake is released, the fixed disc rotates as the drum turns. When the brake is applied, brake caliper (7) grips fixed disc (6). This prevents the drum from turning.
Hydraulic Schematic of Secondary/Parking Brake System
(1) Cooling and test manifold. (2) Steer pump. (3) Pressure switch. (4) Brake valve. (5) Brake switch. (7) Brake caliper. (8) Hose to oil cooler and hydraulic return filter. (9) Hose to hydraulic oil tank.
Steer Pump (2)
Hydraulic oil for the brake system comes from the secondary outlet of the steer pump (2).
Reference: For information on steer pump (2), see Steering Systems Operation Testing and Adjusting, Form No. KEBR2249.
Pressure Switch (3) and Brake Valve (4)
Oil from steer pump (2) is routed to brake valve (4). The brake valv consists of two normally-open solenoid valves, a relief valve, a check valve, and a hydraulic accumulator, all installed in an aluminum body.
Pressure switch (3) and the two solenoid valves are electrically connected to brake switch (5). This controls the flow of oil through the system.
Brake Switch (5)
When the operator pushes brake switch (5) down, oil is ported through brake valve (4) to hose (9). Oil flows through hose (9) to the hydraulic oil tank. This causes brake caliper (7) to remain in the spring-applied position, stopping the machine or holding it in place. A lamp, located in brake switch (5), will light. This indicates that the brake is applied, and the machine should not be moved.
When the operator pulls brake switch (5) up, oil enters brake valve (4) and is routed to brake caliper (7), pressure switch (3), and to the accumulator. If hydraulic oil pressure is high enough, the accumulator is charged and the brake caliper is released. Pressure switch (3) opens, causing oil to be routed through brake valve (4) to hose (8). Oil flows through hose (8) to an oil cooler and hydraulic return filter, and is routed to the hydraulic oil tank. The lamp in brake switch (5) will be dark. This indicates that the brake is released and the machine may be moved.
Reference: For information on the oil cooler and hydraulic return filter, see Steering Systems Operation Testing and Adjusting, Form No. KEBR2249.
Cooling and Test Manifold (1)
Hydraulic oil to the brake caliper is also routed to cooling and test manifold (1). Test port X4 on the cooling and test manifold can be used to measure the pressure of the oil to the brake caliper.
Electrical System
Electrical Schematic of Secondary/Parking Brake System
(1) Brake switch. (2) Contact. (3) Button. (4) Contact. (5) Lamp. (6) Contact. (7) Pressure switch. (8) Contact. (9) Contact. (10) Pressure solenoid. (11) Brake solenoid.
Introduction
Oil flow through the brake valve is electrically controlled by brake switch (1) and pressure switch (7). The operator sets the position of brake switch (1) by pushing button (3) down, or pulling it up. The position of pressure switch (7) is determined by the pressure of the hydraulic oil in the system.
The positions of brake switch (1) and pressure switch (7) determine whether electrical current is sent to pressure solenoid (10) and brake solenoid (11). These two solenoid valves (10) and (11) determine whether hydraulic oil is sent to release the brake caliper.
Brake Applied
Electrical current enters brake switch (1) at contact (2). When the operator pushes button (3) down, contacts (2) and (4) are open, as illustrated. No current is sent to brake solenoid (11). Hydraulic oil is ported through the normally-open brake solenoid (11) to the hydraulic oil tank. Oil pressure in the brake valve is too low to release the brake. Pressure switch (7) is in its normally-closed position.
Electrical current at contact (2) is routed to contact (8) of pressure switch (7). Because the pressure switch is closed, a circuit is made from contact (8) to contact (9). Current flows through pressure switch (7) to pressure solenoid (10) and to contact (6) of brake switch (1). Pressure solenoid (10) is energized (closed). This makes the brake valve ready to send oil to the brake caliper when the operator lifts button (3). Current at contact (6) lights lamp (5), illuminating button (3) on operator's console. This indicates to the operator that the brake is applied.
Brake Released
When the operator pulls button (3) up, contacts (2) and (4) close. Electrical current enters brake switch (1) at contact (2). This current is routed through contact (4) to brake solenoid (11), and through contact (2) to pressure switch (7).
Current from contact (4) energizes brake solenoid (11). Current from contact (2) passes through the closed pressure switch (7), energizing pressure solenoid (10) and lighting lamp (5). Both solenoid valves (10) and (11) are closed.
Hydraulic oil entering the brake valve is routed to the accumulator, the brake caliper, and the pressure switch. The pressure of this oil charges the accumulator, releases the brake caliper, then opens the pressure switch (7). When pressure switch (7) opens, the circuit from contact (8) to contact (9) is broken. Pressure solenoid (10) is de-energized and lamp (5) becomes dark. This indicates to the operator that the brake is released and the machine may be moved. Brake solenoid (11) remains energized (closed) as long as the brake is released.
Hydraulic oil is ported through pressure solenoid (10) to an oil cooler and a hydraulic return filter. A check valve, located in the brake valve body, prevents pressure at the brake caliper from flowing back through the system. Hydraulic oil stored in the accumulator keeps the brake released by making up for small amounts of leakage.
If hydraulic pressure decreases below the setting of pressure switch (7), the pressure switch will close. Pressure solenoid (10) will energize and lamp (5) will flash on for a moment while the system recharges.
Brake Valve Operation
Brake Applied
Brake Valve (Brake Applied)
(1) Pressure solenoid. (2) Pressure port. (3) Aluminum body. (4) Relief valve. (5) Return port. (6) Check valve. (7) Tank port. (8) Brake solenoid. (9) Pressure switch port. (10) Brake port. (11) Accumulator.
Hydraulic oil from the secondary outlet of the steer pump enters brake valve at pressure port (2). This oil is ported to relief valve (4), pressure solenoid (1), and check valve (6). Relief valve (4) protects the system from high-pressure spikes. If the pressure of the oil in the system reaches approximately 13 100 kPa (1900 psi), the relief valve will open. Oil will flow through the relief valve and exit the brake valve through port (5).
Because the brake switch (on operator's console) is pushed down, pressure solenoid (1) is energized (closed). Oil flows past pressure solenoid (1) to check valve (6). Oil opens the check valve and is ported to brake solenoid (8).
Brake solenoid (8) is de-energized (open). Oil is ported through brake solenoid (8) to tank port (7). Oil exits the brake valve through tank port (7) and is routed directly to the hydraulic oil tank.
Oil also flows past brake solenoid (8) to pressure switch port (9), brake port (10), and accumulator (11). Oil exits the brake valve through ports (9) and (10), and is routed to the pressure switch and the brake caliper. The pressure of this oil will be approximately 1030 kPa (150 psi). This pressure is too low to release the brake or open the pressure switch.
Brake Charging
Brake Valve (Brake Charging)
(1) Pressure solenoid. (2) Pressure port. (3) Aluminum body. (4) Relief valve. (5) Return port. (6) Check valve. (7) Tank port. (8) Brake solenoid. (9) Pressure switch port. (10) Brake port. (11) Accumulator.
When the operator pulls brake switch up, pressure solenoid (1) and brake solenoid (8) are both energized. Hydraulic oil from the secondary outlet of the steer pump enters the brake valve at pressure port (2). This oil is ported to relief valve (4), pressure solenoid (1), and check valve (6).
Relief valve (4) protects the system from high-pressure spikes. If the pressure of the oil in the system reaches approximately 13 100 kPa (1900 psi), the relief valve will open. Oil will flow through the relief valve and exit the brake valve through port (5).
Oil flows past the energized (closed) pressure solenoid (1) to check valve (6). Oil opens the check valve and is ported to brake solenoid (8). Oil flows past the energized (closed) brake solenoid (8), to pressure switch port (9), brake port (10), and accumulator (11).
The pressure of this oil charges accumulator (11). As the accumulator charges, pressure of the oil increases. When the oil pressure reaches 10 000 kPa (1450 psi), brake caliper releases. When the oil pressure reaches 10 340 kPa (1500 psi), pressure switch opens, de-energizing pressure solenoid (1). The brake is now released.
Brake Released
Brake Valve (Brake Released)
(1) Pressure solenoid. (2) Pressure port. (3) Aluminum body. (4) Relief valve. (5) Return port. (6) Check valve. (7) Tank port. (8) Brake solenoid. (9) Pressure switch port. (10) Brake port. (11) Accumulator.
When the brake is charging, oil pressure in the brake valve charges the accumulator, releases the brake caliper, and opens the pressure switch. When the pressure switch opens, pressure solenoid (1) is de-energized.
Hydraulic oil from the secondary outlet of the steer pump enters the brake valve at pressure port (2). This oil is ported through pressure solenoid (1) to port (5). Oil exits the brake valve through port (5), and is routed through an oil cooler and hydraulic return filter, to the hydraulic oil tank.
Reference: For information on the oil cooler and hydraulic return filter, see Steering Systems Operation Testing and Adjusting, Form No. KEBR2249.
Check valve (6) is closed. This prevents high-pressure oil from flowing backward through the brake valve. Brake solenoid (8) is energized. This prevents high-pressure oil from flowing out through tank port (7).
Accumulator (11) acts as a source of high-pressure oil to pressure switch port (9) and brake port (10). This makes up for small amounts of oil leakage, and keeps the brake released and the pressure switch open.
If accumulator (11) becomes discharged, oil pressure may drop below 10 340 kPa (1500 psi). If this occurs, the pressure switch will open and the brake valve will return to the Brake Charging state.
Brake Caliper
Brake Caliper
(1) Pads. (2) Piston. (3) Port. (4) Chamber. (5) Springs.
The brake caliper is a spring-applied hydraulically released brake. The brake caliper is mounted on the right side of the vibratory drum. The fixed disc is mounted to the drum support assembly, and fits between the two brake pads (1).
When the brake is applied, springs (5) move piston (2) to the left. The fixed disc is held between the two pads (1). This prevents the drum from rotating, stopping the machine or holding it in place.
When the brake is released, hydraulic oil enters the brake caliper through port (3). The pressure of the oil moves piston (2) to the right, compressing springs (5). This creates a space between the fixed disc and the pads (1), allowing the drum to rotate freely.