PLATE 3650720 - Caterpillar

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 Engaged
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 engaged.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