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Systems Operation 994D Wheel Loader Braking System

General Information SMCS - 4250

Media Number - RENR2511-01 Publication Date - 1999/06/01 Date Updated - 2001/10/09

Illustration 1

Braking System Schematic

(1) Oil cooler for the steering and brake systems

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(2) Check valve for the oil cooler bypass

(3) Neutralizer valve for the torque converter

(5) Check valve

(6) Brake cooling screen

(7) Fluid sampling valve

(8) Filter for the steering and brake oil cooler "STRG COOL FLTR"

(9) Pressure switch for the oil filter

(10) Left pedal

(11) Service brake valve

(12) Service brakes

(13) Parking brake

(14) Brake accumulators

(15) Gear pump for the steering and brake oil cooler

(16) Pressure switch for the brake accumulators "BRK ACUM PRES"

(17) Service brake pedal

(18) Parking brake control valve

(19) Check valve

(20) Brake pump

(21) Pressure compensator valve

(22) Check valve for the oil cooler bypass

(23) Pressure switch for the parking brake "PARKBRK SW"

(24) Oil cooler for the brake cooling circuit

(25) Gear pump for the brake cooling circuit

(26) Hydraulic tank for the steering and brake systems

(27) Hydraulic tank for the brake cooling circuit

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Illustration 2

(1) Oil cooler for the steering and brake systems

(2) Check valve for the oil cooler bypass

(3) Neutralizer valve for the torque converter

(5) Check valve

(6) Brake cooling screen

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Brake System Brake pump (20) draws oil from hydraulic tank (26) for the steering and brake systems. The brake pump is a variable displacement piston pump. Pressure compensator valve (21) senses the load requirements of the brake system. The pressure compensator valve maintains the oil pressure to the brake system by either upstroking or destroking the brake pump.

The oil then flows through check valve (19) to brake accumulators (14). The pressure oil from the brake pump 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 destrokes the brake pump. Check valve (19) prevents the flow of pressure oil to the brake pump from the brake

(7) Fluid sampling valve

(8) Filter for the steering and brake oil cooler "STRG COOL FLTR"

(10) Left pedal

(11) Service brake valve

(12) Service brakes

(13) Parking brake

(14) Brake accumulators

(15) Gear pump for the steering and brake oil cooler

(16) Pressure switch for the brake accumulators "BRK ACUM PRES"

(17) Service brake pedal

(18) Parking brake control valve

(19) Check valve

(20) Brake pump

(21) Pressure compensator valve

(22) Check valve for the oil cooler bypass

(23) Pressure switch for the parking brake "PARKBRK SW"

(24) Oil cooler for the brake cooling circuit

(25) Gear pump for the brake cooling circuit

(26) Hydraulic tank for the steering and brake systems

(27) Hydraulic tank for the brake cooling circuit

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accumulators.

The brake accumulators provide pressure oil to the following components: service brake valve (11), neutralizer valve (3) and parking brake control valve (18) .

The oil then flows to pressure switch (16) and service brake valve (11). Pressure switch (16) monitors the pressure of the oil from the brake accumulators. The Vital Information Management System (VIMS) monitors pressure switch (16). The VIMS will display a warning if the pressure is lower than 6890 ± 345 kPa (1000 ± 50 psi).

When service brake pedal (17) is depressed, service brake valve (11) directs pressure oil from the brake accumulators to service brakes (12). The pressure oil activates the service brakes. When the pedal is released, the service brakes are also released.

There is a limit switch that is mounted behind the service brake pedal. The limit switch is monitored by the Engine Electronic Control Module (ECM). This signals the Engine ECM that the service brake pedal is depressed. This also signals the ECM for the power train that the service brake pedal is depressed.

Left pedal (10) is connected to a bellcrank assembly by the service brake control. The left pedal controls neutralizer valve (3) as well as service brake valve (11) through the bellcrank assembly.

Note: For additional information on adjusting the bellcrank assembly, refer to the following manual: Specifications, RENR2510, "994D Wheel Loader Braking System", "Brake Control".

When the left pedal is depressed, there is a small initial deadband. After this deadband, the bellcrank actuates the neutralizer valve. This allows pressure oil from the brake accumulators to enter the neutralizer valve.

As the left pedal is depressed further, the bellcrank assembly actuates the service brake valve. This allows pressure oil to flow to the service brakes. This pressure oil activates the service brakes.

When the left pedal is released, the service brake valve and the neutralizer valve deactivate. This allows the service brakes to release.

Pressure oil also flows to parking brake control valve (18). When the parking brake control valve is in the ENGAGED position, the flow of oil to parking brake (13) is blocked. This causes the parking brake to remain engaged. When the parking brake valve is in the DISENGAGED position, pressure oil flows to pressure switch (23) and parking brake (13). This causes the parking brake to release.

The ECM for the power train monitors pressure switch (23). 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.

Note: The ECM for the power train is also called the Transmission Electronic Control.

Cooling Circuit for the Steering and Brake Systems Gear pump (15) draws hydraulic oil from hydraulic tank (26). The oil then passes through filter (8). The filter removes any debris that is in the hydraulic oil. This prevents contamination of the oil that is in the

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hydraulic tank for the steering and brake systems.

A bypass valve in the filter allows the hydraulic oil to bypass the oil filter. This occurs when the flow of oil through the filter is restricted and an adequate oil flow cannot be maintained. This also occurs in cold start-up conditions when the hydraulic oil is cold. Pressure switch (9) actuates when the flow of oil through the filter is restricted. Pressure switch (9) is monitored by the VIMS. The VIMS will display a warning when the flow of oil through the filter is restricted.

The hydraulic oil then flows to oil cooler (1) for the steering and brake systems. Check valve (2) for the oil cooler bypass allows the hydraulic oil to bypass the oil cooler. This occurs when the hydraulic oil is cold. The hydraulic oil then flows to hydraulic tank (26) for the steering and brake systems.

Fluid sampling valve (7) is available for scheduled oil sampling analysis (S·O·S analysis). The fluid sampling valve is mounted to gear pump (15) for the cooling circuit.

Note: For additional information on the VIMS, refer to Service Manual, SENR6059, "Vital Information Management System (VIMS)".

Brake Cooling Circuit The heat that is generated by the application of service brakes (12) is removed by a separate flow of hydraulic oil.

Gear pump (25) for the brake cooling circuit draws oil from hydraulic tank (27). The oil then flows through oil cooler (24). Check valve (22) for the oil cooler bypass allows the hydraulic oil to bypass the oil cooler. This occurs when the hydraulic oil is cold.

The oil then flows to service brakes (12). Then, the oil flows between the discs and the plates that are within the service brakes in order to absorb the heat that is generated by the friction. The oil then flows out of the service brakes and through brake cooling screens (6). The brake cooling screens remove any debris that is in the hydraulic oil. This prevents contamination of the oil that is in the cooling circuit.

The cooling oil then flows through check valves (5) to hydraulic tank (27). Check valves (5) prevent oil from flowing back through the brake cooling screens.

Location of the Brake System Components

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Brake pump (20) is located in the compartment that is in front of the engine compartment. The brake pump is mounted on the back of the rear pump drive on the right side. Pressure compensator valve (21) is mounted on the brake pump. Access is gained by removing the panel on the right side of the engine end frame.

The following items are located in the compartment above the rear pump drive: filter (8) for the steering and brake systems, hydraulic tank (26) for the steering and brake systems and hydraulic tank (27) for the brake cooling circuit. Pressure switch (9) is installed in the base of filter (8) .

Brake accumulators (14) are located in the compartment behind the operator compartment. The brake

Illustration 3 View of the Brake Pump

(20) Brake pump. (21) Pressure compensator valve.

Illustration 4 View of the Hydraulic Tanks

(8) Filter for the steering and brake systems. (26) Hydraulic tank for the steering and brake systems. (27) Hydraulic tank for the brake cooling circuit.

The VIMS refers to the filter for the steering and brake systems as "STRG COOL FLTR".

Illustration 5 View of the Brake Accumulators

(14) Brake accumulators. (19) Check valve.

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accumulators are mounted on the right side of the engine end frame.

The brake control is located in the compartment behind the operator compartment. The brake control is mounted on the left side of the engine end frame.

Illustration 6 View of the Brake Control

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The following components are mounted on the brake control: neutralizer valve (3), service brake valve (11), pressure switch (16) for the brake accumulators, parking brake control valve (18), pressure switch (23) for the parking brake and bellcrank assembly (28) .

Parking brake control knob (29) is located on the dash panel that is in the operator compartment.

Illustration 7 Brake Control

(3) Neutralizer valve for the torque converter

(11) Service brake valve

(16) Pressure switch for the brake accumulators "BRK ACUM PRES"

(18) Parking brake control valve

(23) Pressure switch for the parking brake "PRKBRK SW"

(28) Bellcrank assembly

Illustration 8 View of the Pedals

(10) Left pedal. (17) Service brake pedal. (29) Parking brake control knob.

Illustration 9

Location of the Limit Switch for the Service Brake Pedal

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The limit switch for the service brake pedal is located behind the lower panel.

Parking brake (13) is mounted on the non-engine end frame. The parking brake is connected to the front drive shaft.

Gear pump (15) is located in the compartment that is in front of the engine compartment. The gear pump is mounted on the back side of the rear pump drive on the left side. Access is gained by removing the panel on the left side of the engine end frame. Fluid sampling valve (7) is located under the gear pump.

The VIMS refers to the limit switch for the service brake pedal as "SVC BRK PDL SW".

Illustration 10 View of the Parking Brake

(13) Parking brake.

Illustration 11 View of the Gear Pump for the Cooling Circuit

(7) Fluid sampling valve. (15) Gear pump.

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Oil cooler (1) for the steering and brake systems is located between the cooling fan and the radiator assembly.

Gear pump (25) for the brake cooling circuit is located in the compartment behind the operator compartment. The gear pump is mounted on left steering pump (30). The steering pump is mounted on the front side of the rear pump drive.

Illustration 12 View of the Oil Cooler for the Steering and Brake Systems

(1) Oil cooler.

Illustration 13 View of the Gear Pump for the Brake Cooling Circuit

(25) Gear pump. (30) Left steering pump.

Illustration 14

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Bypass check valve (22) and oil cooler (24) are located on the left side of the engine end frame. The oil cooler is mounted above the rear axle assembly.

Brake cooling screens (6) are mounted on the sides of the front axle assembly and the rear axle assembly.

Check valves (5) are mounted on the top of the front axle assembly and the rear axle assembly.

View of the Oil Cooler for the Brake Cooling Circuit

(22) Check valve for the oil cooler bypass. (24) Oil cooler for the brake cooling circuit.

Illustration 15 View of a Brake Cooling Screen

(6) Brake cooling screen.

Illustration 16 View of a Check Valve for the Brake Cooling Circuit

(5) Check valve.

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