992K Wheel Loader Caterpillar

Illustration 1	g06155305
Main hydraulic schematic for the braking system (1) Front service brakes (2) Hydraulic oil temperature sensor for the front service brakes (3) Parking brake (4) Parking brake limit switch (5) Parking brake pressure switch (6) Brake pedals (7) Service brake control valve (8) Parking brake control valve (9) Accumulator for the front service brakes (10) Accumulator for the rear service brakes (11) Pressure switch for the accumulator for the front service brakes and for the accumulator for the rear service brakes (12) Brake accumulator charging valve (13) Oil pressure sensor for the front service brakes (VIMS) (14) Oil pressure sensor for the rear service brakes (VIMS) (15) Check valve for the parking brake release (16) Check valve for the brake pump (17) High-pressure screen (18) Brake manifold (19) Hydraulic oil tank for the steering system and for the braking system (20) Breaker relief valve (21) Relief valve (22) Hydraulic oil temperature sensor for the rear service brakes (23) Rear service brakes (24) Brake pump (A) Pressure port for the front service brakes (B) Pressure port for accumulator (10) ( C) Pressure port for accumulator (9) ( D) Pressure port for the front service brakes (E) Pressure port for the rear service brakes (F) Pressure port for the rear service brakes

Note: To determine the general location of a main brake system component, refer to the section for the appropriate description of the component.

Illustration 2	g02710630
Left side view

Illustration 3	g02710713
(17) High-pressure screen

High-pressure screen (17) (if equipped) is located by the transmission oil filler tube on the left side of the machine. High-pressure screen (17) contains a screen that protects the hydraulic system in a component failure. The high-pressure screen may be removed and cleaned.

Case drain filter is located under the access door in the cab platform. Case drain filter provides additional protection of the hydraulic system against contaminants.

Differential pressure switch is for case drain filter.

Breaker relief valve (20) is part of hydraulic oil tank (19) for the steering system and for the braking system. Breaker relief valve (20) controls the amount of vacuum and the amount of pressure buildup in the hydraulic oil tank (19).

Illustration 4	g01439039
Left side view

Illustration 5	g01435566
(24) Brake pump

Brake pump (24) is a variable displacement piston pump. The brake pump draws oil from hydraulic oil tank (19). A pressure control valve on the pump senses the load requirements of the brake circuit. The pressure control valve then maintains the pressure by upstroking the pump or by destroking the pump.

Check valve (16) is for the brake pump (24). The check valve is located in brake accumulator charging valve (12). This check valve helps to reduce pressure spikes that may be in the brake circuit.

Illustration 6	g02694279
Left side view

Illustration 7	g02694116
(9) Accumulator for the front service brakes (10) Accumulator for the rear service brakes (12) Brake accumulator charging valve

Illustration 8	g02694218
(9) Accumulator for the front service brakes (10) Accumulator for the rear service brakes

The brake accumulator charging valve (12) allows the oil to flow to front accumulator (9) and to rear accumulator (10). The brake accumulator charging valve (12) contains the shuttle valve . This action directs the brake oil supply to the brake accumulator.

If the pressure in one accumulator is less than the pressure oil from brake pump (24), the check valve for that accumulator will allow the pressure oil to charge the accumulator. If pressure output from brake pump (24) decreases, check valve (16) will prevent pressure oil from flowing back to the brake pump from the accumulators. The shuttle valve is located in the brake accumulator charging valve (12). If, the pressure drops the accumulators will still receive oil.

The accumulators store energy for the front service brakes (1) and for the rear service brakes (23). Also, the accumulators supply oil for the front service brakes and for the rear service brakes. Additionally, accumulator (10) stores energy for the parking brake circuit. Accumulator (10) also supplies oil for the parking brake circuit.

Illustration 9	g02712059
Left side view

Illustration 10	g00104382
Location of the service brake control valve (7) Service brake control valve

Illustration 11	g02682768
(6) Brake pedals

The oil then flows to brake manifold (18). Brake manifold routes the oil to service brake control valve (7). When either brake pedal (6) is depressed, the pressure oil flows through service brake control valve (7). When service brake control valve (7) actuates, pressure oil flows to front service brakes (1) and to rear service brakes (23).

Depressing either brake pedal (6) causes spool movement in service brake control valve (7). This action allows oil from the accumulators to flow to front service brakes (1) and to rear service brakes (23).

Illustration 12	g02696556
Left side view

Illustration 13	g02696576
(A) Pressure port for the front service brakes (F) Pressure port for the rear service brakes

There are several pressure taps on this machine. Pressure tap (A) is for the front service brakes. Pressure tap (F) is for the rear service brakes.

Illustration 14	g02711228
Right side view

Illustration 15	g02710717
(13) Oil pressure sensor for the front service brakes (14) Oil pressure sensor for the rear service brakes (15) Check valve for the parking brake release (18) Brake manifold

Illustration 16	g02694279
Left side view

Illustration 17	g02712061
(11) Accumulator pressure switch

Pressure switch (11) is for the accumulator for the front and rear service brakes. The location of the pressure switch (11) is shown above.

If the machine is equipped with the Vital Information Management System (VIMS), two oil pressure sensors will be located on brake manifold (18). Oil pressure sensor (13) is for the front service brakes. Oil pressure sensor (14) is for the rear service brakes.

Illustration 18	g02696897
Left side view

Illustration 19	g02696916
(5) Parking brake pressure switch (8) Parking brake control valve

Parking brake release check valve (15) is in the drain line from the parking brake line. The oil also flows into parking brake control valve (8). Accumulator (10) also provides pressure oil for parking brake control valve (8). Pressure oil also flows to parking brake pressure switch (5).

When parking brake control valve (8) moves to the disengaged position, oil from the accumulator flows through parking brake control valve (8). The oil then flows to the parking brake. This causes parking brake (3) to disengage.

Illustration 20	g01439110
Left side view

Illustration 21	g02712041
Location of parking brake (3) Parking Brake

Parking brake (3) engages automatically when the supply pressure from the accumulators drops below 6890 ± 345 kPa (1000 ± 50 psi). This causes parking brake pressure switch (5) to open.

When the oil pressure increases to approximately 8270 kPa (1200 psi), parking brake pressure switch (5) closes. This action stops the alarm for the Warning Category 3 if the transmission was in a forward speed position or in a reverse speed position. However, if the transmission was in NEUTRAL, the Warning Category 1 would stop.

Parking brake limit switch (4) functions as an override switch for the transmission.

Axle Oil Cooler

Illustration 22	g06155557
Hydraulic schematic for the axle oil cooler (26) Screen group for the front axle (27) Screen group for the rear axle (28) Thermal bypass valve for the rear axle (29) Rear service brakes (30) Rear brake manifold (31) Front brake manifold (32) Front service brakes (33) Axle oil cooler for the rear axle (34) Axle oil cooler for the front axle (35) Thermal bypass valve for the front axle (36) Axle oil cooler pump for the rear axle (37) Axle oil cooler pump for the front axle (38) Steering pilot pump (39) The motor for the axle oil cooler (40) The ON OFF diverter valve for the axle oil cooler (41) The relief valve for the axle oil cooler system (42) Steering pilot relief valve (43) Pilot filter for the steering

Axle oil cooler pumps (36) and (37) circulate the oil which flows through both axle housings. When cooling for the axle oil is needed, flow from steering pilot pump (38) flows through the ON and OFF diverter valve (40) in order to drive the cooling motor (39). The cooling motor for the axle oil is mechanically connected to cooling pumps (36) and (37). Output flow from the motor of the axle oil cooler (39) flows to the pilot filter for steering (43) and relief valve (42).

Rear axle oil cooler pump (36) circulates the oil through screen group (27). When the engine is started and the axle oil is cold, the oil from rear axle oil cooler pump (36) cannot easily flow through axle oil cooler (33). The oil pressure will increase in the rear axle oil cooler (33) and thermal bypass valve (28) will open. The thermal bypass valve (28) limits the maximum oil pressure in rear axle oil cooler (33) to 586 ± 69 kPa (85 ± 10 psi). When the temperature of the oil increases, the pressure of the oil decreases. When the spring force is greater than the force of the oil pressure, thermal bypass valve (28) will close. The axle oil flows through axle oil cooler (33). From rear axle oil cooler (33), oil circulates through the rear brake manifold (30) and through the brake housing of rear axle (29).

Front axle oil cooler pump (37) circulates the oil through screen group (26). When the engine is started and the axle oil is cold, the oil from front axle oil cooler pump (37) cannot easily flow through screen group (26). The oil pressure will increase in the front axle oil cooler (34) and thermal bypass valve (35) will open. The thermal bypass valve (35) limits the maximum oil pressure in the front axle oil cooler (34) to 586 ± 69 kPa (85 ± 10 psi). When the temperature of the oil increases, the pressure of the oil decreases. When the spring force is greater than the force of the oil pressure, thermal bypass valve (35) will close. The front axle oil flows through axle oil cooler (34). From front axle oil cooler (34), oil circulates through the front brake manifold (31) and through the brake housing of front axle (32).

Illustration 23	g02693538
(2) Hydraulic oil temperature sensor for the front service brakes

Illustration 24	g02693542
(22) Hydraulic oil temperature sensor for the rear service brakes

Hydraulic oil temperature sensor (2) for the front service brakes is located on the front axle housing. Hydraulic oil temperature sensor (22) for the rear service brakes is located on the rear axle housing.

The hydraulic oil temperature sensors activate a warning in the cab when the temperature of the oil reaches approximately 90°C (194°F). When the temperature of the oil cools to approximately 85°C (185°F), the warning stops.