994K Wheel Loader Machine Systems Caterpillar

Illustration 1	g03866594
Brake system component locations (1) Brake hydraulic oil tank (2) Parking brake operator switch (3) Service brake control valve (4) Service brake pedal (5) Service brakes (6) Parking brake assembly (7) Engine ECM (8) Transmission ECM (9) Brake pump (10) Parking brake solenoid valve (11) Control manifold (12) Brake relief valve (13) Brake screen (14) Brake accumulators

Illustration 2	g03879075
(1) Brake hydraulic oil tank (3) Service brake control valve (4) Service brake Pedal (5) Service brakes (6) Parking brake assembly (8) Transmission ECM (9) Brake pump (9A) Control valve (part of (9)) (10) Parking brake solenoid valve (11) Control manifold (12) Brake relief valve (13) Brake screen (14) Brake accumulators (15) Manifold (A) Parking brake oil pressure sensor (B) Brake accumulator pressure sensor

Brake System

Brake pump (9) draws oil from brake hydraulic oil tank (1) for the hydraulic brake system. The brake pump is a variable displacement piston pump. Control valve (9A) in the brake pump senses the load requirements of the hydraulic brake system. The control valve maintains the oil pressure to the hydraulic brake system by either upstroking or destroking the brake pump. The oil next flows to brake screen (13), control manifold (11), and brake accumulators (14). Brake relief valve (12) maintains the oil pressure in the brake accumulators. When the pressure of the oil in the brake accumulators equals 16000 ± 345 kPa (2320 ± 50 psi) the pressure compensator valve in the brake pump destrokes the brake pump. A check valve in control manifold (11) prevents the flow of pressure oil back from brake accumulators (14) in the case of a hose failure or loss of oil pressure in the hydraulic brake system supply circuit. Brake accumulator pressure sensor (B) monitors the pressure of the oil in the brake accumulators and signals the Vital Information Management System (VIMS) . The VIMS will display a warning if the pressure is lower than 6890 ± 345 kPa (1000 ± 50 psi).

Pressure oil flows through manifold (15) and to service brake control valve (3). When either service brake pedal (4) is depressed, stop lamps are activated and service brake control valve (3) actuates and pressure oil flows to front and rear service brakes (5). When only the left service brake pedal is depressed, impeller clutch pressure and the amount of power through the drive train is limited. This action provides more engine power for the rest of the hydraulic system. Depressing the left service brake pedal assembly even farther actuates the service brakes at each wheel. When the left service brake pedal is released, service brake control valve (3) and the impeller clutch deactivate. This action allows service brakes (5) to release.

Pressure oil also flows to parking brake solenoid valve (10). When parking brake solenoid valve (10) is in the ENGAGED position, the flow of oil to parking brake assembly (6) is blocked and the pressure oil is released to brake hydraulic oil tank (1). This action enables parking brake assembly (6) to engage. When parking brake solenoid valve (10) is in the DISENGAGED position, pressure oil flows to parking brake oil pressure sensor (A) and parking brake assembly (6). This action causes parking brake assembly (6) to disengage. Refer to System Operation, "Parking Brake" for more details.

Transmission ECM (8) monitors parking brake oil pressure sensor (A). When the pressure is lower than 6890 ± 345 kPa (1000 ± 50 psi), the VIMS will display a warning. This warning indicates that the parking brake is engaged.