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Systems Operation769D & 771D TRUCKS STEERING SYSTEM

Systems Operation

SMCS - 7566

Introduction

NOTE: For Specifications with illustrations, make reference to the Specifications For 769D & 771DTruck, Steering System, SENR8613. If the Specifications in SENR8613 are different than in theSystems Operation, Testing & Adjusting, look at the printing date on the front cover of each module.Use the Specifications given in the module with the latest date.

Steering Hydraulic Schematic

Schematic Of Steering Hydraulic System

Shutdown

Previous Screen

Product: QUARRY TRUCK

Model: 769D QUARRY TRUCK 5TR

Configuration: 769D Truck 5TR00505-UP (MACHINE) POWERED BY 3408EEngine

Media Number -SENR8614-00 Publication Date -31/01/1996 Date Updated -12/10/2001

Pgina 1 de 12769D Truck 5TR00505-UP (MACHINE) POWERED BY 3408E Engine(SEBP275...

23/02/2006https://fsalima31/sisweb/sisweb/techdoc/techdoc_print_page.jsp?returnurl=/sisweb/sis...

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(1) Oil [at pump pressure]. (2) Oil [blocked]. (3) Oil [at tank pressure]. (4) Hand Metering Unit [HMU]. (5) Rightcylinder. (6) Hydraulic tank. (7) Supplemental electric motor. (8) Relief valve [for cylinders]. (9) Oil filter. (10)Manual/auto panel switch. (11) Magnetic switch. (12) Electronic control module. (13) Check valve. (14) Relief valve [inflow control valve]. (15) Supplemental pump [two-section brake and steering]. (16) Pump [steering]. (17) Flow controlvalve. (18) Left cylinder. (19) Flow switch.

Steering Oil Lines

Top View(5) Right cylinder. (6) Hydraulic tank. (8) Relief valve [for cylinders]. (9) Oil filter. (13) Check valve. (16) Pump[steering]. (17) Flow control valve. (18) Left cylinder.



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Side View(4) Hand Metering Unit [HMU]. (6) Hydraulic tank. (8) Relief valve [for cylinders]. (9) Oil filter. (13) Check valve. (14)Relief valve [in flow control valve]. (16) Pump [steering]. (17) Flow control valve. (18) Left cylinder.

Supplemental Steering Lines



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Top View

(6) Hydraulic tank. (7) Supplemental electric motor. (9) Oil filter. (15) Supplemental pump [two-section brake andsteering]. (16) Pump [steering]. (17) Flow control valve.

General Information

The steering system is all hydraulic. There is no mechanical connection between the steering wheeland cylinder (5) and cylinder (18) that move the front wheels to turn the machine. The majorcomponents of the steering system are pump (16), Hand Metering Unit [HMU] (4), hydraulic tank(6), relief valve (8) for cylinders, flow control valve (17), cylinder (5) and cylinder (18). The steeringsystem is independent of all other hydraulic systems.



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(16) Pump [steering]. (20) Pump [hoist]. (21) Pump [transmission]. (22) Oil pump drive.

Oil pump drive (22) with three hydraulic pumps, is connected to the engine by a drive shaft. Theengine must be operating for pump (16) to operate the hydraulic steering system. If the engine stopswhile the truck is moving, supplemental electric motor (7) is automatically activated. When thesteering wheel is moved, the supplemental pump (15) sends a limited amount of oil to cylinder (5)and cylinder (18) to turn the truck.

Pump (16) is a one-section gear pump. The steering pump (16), hoist pump (20) and transmissionpump (21) are all on oil pump drive (22) connected to the engine by a U-joint. The oil pump drive islocated between the frame and engine, on the left side, at the rear of the engine.

Flow Control Valve(13) Check valve. (14) Relief valve. (17) Flow control valve.

Pump (16) gets oil from hydraulic tank (6). Pump (16) moves the oil through flow control valve (17),where the flow of oil from the pump is divided. Some of the oil flows back through oil filter (9) andinto hydraulic tank (6).

If the steering wheel is not turned, the oil in Hand Metering Unit [HMU] (4) flows through and back

to flow control valve (17). In this case, all of the oil from pump (16) flows through oil filter (9) andback into hydraulic tank (6).

When the steering wheel is turned in a counterclockwise direction to turn the truck to the left, thepump oil in HMU (4) flows to the head end of right cylinder (5) and to the rod end of left cylinder(18). The action of the oil on the pistons and rods in cylinder (5) and cylinder (18) turn the frontwheels of the truck to make a left turn. The oil from the rod end of right cylinder (5) and the headend of left cylinder (18) flows back through HMU (4), flow control valve (17) and through oil filter(9) into hydraulic tank (6).

The amount of oil flow from HMU (4) is in relation to the speed the steering wheel is turned. Turn

the steering wheel slow and the front wheels change direction slowly, turn it fast and the frontwheels change direction faster.



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The oil from pump (16) is limited to a maximum pressure of approximately 15 100 kPa (2190 psi) byrelief valve (14) in flow control valve (17).

The blocked oil in cylinder (5) and cylinder (18) and in the lines between the cylinders and HMU(4), prevents a change in direction of the wheels when the steering wheel is not turned.

If a front wheel would strike against a large object that can not move, the pressure of the oilincreases in one end of each cylinder and in the oil lines connected to those ends. If the increase inoil pressure gets to approximately 18 270 kPa (2650 psi), relief valve (8) for the cylinders opens. Oilcan then flow between the head ends and rod ends of the cylinders.

The supplemental pump (15) provides oil to steer the front wheels if the normal flow is lost frompump (16) or engine failure. The location of supplemental pump (15) is under the frame, behind theengine and directly above the torque converter.

Instrument Panel(10) Manual/Automatic panel switch [for supplemental steering]. (23) Caterpillar Electronic Monitoring System [CEMS]action light. (24) Supplemental steering indicator light. (25) Steering alert indicator light.

Supplemental pump (15) operates according to the position of manual/automatic panel switch (10).During normal machine operation, manual/automatic panel switch (10) is put in the "AUTO"

position. When the engine is started, electric control module (12) turns on supplemental electricmotor (7) which operates supplemental pump (15) for a three second period of time. Supplemental

steering indicator light (24) also comes on during that time.

The Caterpillar Electronic Monitoring System [CEMS] is designed to alert the operator of animmediate or impending problem in the steering or other machine systems.

If the engine stops while there is movement of the machine, flow switch (19) activates electroniccontrol module (12). Electronic control module (12) turns on magnetic switch (11), which turns onsupplemental electric motor (7) that operates supplemental pump (15). Electronic control module(12) also causes steering alert indicator light (25) and CEMS action light (23) to FLASH and theaction alarm to sound. Supplemental steering indicator light (24) activates when the supplementalsteering system is activated.

Manual/automatic panel switch (10) is moved to the "MANUAL" position only when the machine istowed (pulled). This switch activates supplemental pump (15) and supplemental steering indicator



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light (24).

Electric power for supplemental pump (15) comes from the truck's batteries. When supplementalpump (15) is operating, oil is drawn from hydraulic tank (6). This oil moves through flow controlvalve (17), check valve (13) and into HMU (4). Because of the small flow of oil from supplemental

pump (15), truck steering is slow.

Hand Metering Unit [HMU]

Hand Metering Unit [HMU] Components(1) Input shaft. (2) Ball. (3) Valve spool. (4) Housing. (5) Gear [outside gear of gerotor]. (6) Manifold. (7) Torsion bar.(8) Drive link. (9) Gear [inside gear of gerotor]. (10) Commutator.

Hand Metering Unit [HMU](11) Shaft [from steering wheel]. (12) Oil lines [to cylinders]. (13) Pump oil line. (14) Oil line [to tank].

Shaft (11) from the steering wheel is connected to input shaft (1) in the Hand Metering Unit [HMU].

A pin through input shaft (1) and torsion bar (7) connects the shafts. Torsion bar (7) has a pin drivein the other end that fits into the grooves in drive link (8). The splines on one end of drive link (8)are in the splines in the center of gear (9). Splines on the other end of drive link (8) are in the splines



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in valve spool (3). Drive link (8) also is the drive for commutator (10). Shaft (11), input shaft (1),valve spool (3), torsion bar (7), drive link (8), gear (9) and commutator (10) turn with the steeringwheel.

Ball (2) is in a hole in valve spool (3) and is also in the helical groove around input shaft (1). Wheninput shaft (1) is turned, ball (2) moves in the helical groove and moves (but does not turn) valvespool (3) a short distance. The splines connected to drive link (8) prevent valve spool (3) fromrotating at this point. The movement of valve spool (3) is either toward gear (5) when the steeringwheel is turned clockwise or toward the steering wheel when it is turned counterclockwise. Whenvalve spool (3) is moved to the end of its travel, holes and grooves in the valve spool align withholes and grooves in housing (4).

After valve spool (3) aligns with housing (4), one of oil lines (12) to the cylinders is an outlet for thepump oil to the cylinders. The other oil line (12) is an inlet for the return oil.

When valve spool (3) is moved to the other end of its travel, the opening that was an inlet for thereturn oil is now an outlet for the pump oil to the cylinders and the opening that was an outlet to thecylinders is now an inlet for the return oil.

When valve spool (3) is in the center of its travel, no holes and grooves are in alignment to theopening in housing (4). This blocks the oil in oil lines (12) and the oil in the cylinders. The oil thencirculates through the HMU, flows through the flow control valve and returns to the hydraulic tank.

When the steering wheel turns shaft (11) and input shaft (1), torsion bar (7) can not easily turn drivelink (8) and gear (9) because of the hydraulic oil block in oil lines (12) and the cylinders. The oil

blockage causes resistance to movement of commutator (10), gear (9) and drive link (8) until valvespool (3) moves to allow oil flow. The splines on drive link (8) in valve spool (3) also keep the valvespool from rotating.

When input shaft (1) is rotated, torsion bar (7) gets twisted because it cannot turn drive link (8). Therotation of input shaft (1) also causes ball (2) to move valve spool (3). When valve spool (3) movesto the position that opens the outlet and inlet passages in housing (4) to oil lines (12), torsion bar (7)turns drive link (8). Drive link (8) turns gear (9), commutator (10) and valve spool (3).

As gear (9) turns in gear (5), oil is moved from pump oil line (13) through manifold (6). Then,commutator (10) moves the pump oil to oil lines (12) to the cylinders. Gear (9) rotates with and atthe same speed as the steering wheel. The speed of gear (9) is in relation to the amount of oil itmoves to the cylinders. Turn the steering wheel slowly and the truck is slow to change direction orturn the steering wheel fast and the truck changes direction fast.

Stop turning the steering wheel, and the twisted torsion bar (7) will rotate drive link (8) in theopposite direction of the original steering wheel rotation until the torsion bar is no longer twisted. Asdrive link (8) rotates, it moves valve spool (3) and ball (2) reverses its path around the helical groovein input shaft (1). This moves valve spool (3) to the center position where the holes and grooves aremisaligned. This causes a hydraulic oil block in oil lines (12) and in the cylinders and the frontwheels stop their change in direction.

Timing Of Hand Metering Unit [HMU] Drive



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(1) Pin. (2) Drive. (3) Timing mark. (4) Gerotor star valleys. (A), (B), and (C) are reference lines.

If the Hand Metering Unit [HMU] is disassembled for any reason, it must be put back together withthe relationship between gerotor star valleys (4) and pin (1) as shown. Otherwise, erratic steeringwill result. To assemble correctly, use timing mark (3) located on drive (2).

Timing mark (3) on drive (2) must fall on the parallel line between any two gerotor star valleys (4).Note parallel relationships of reference lines (A), (B), and (C).

Flow Control Valve And Relief Valve



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Flow Control Valve(1) Orifice. (2) Opening [to the Hand Metering Unit (HMU)]. (3) Relief valve. (4) Adjustment screw. (5) Opening [fromthe HMU]. (6) Check valve. (7) Opening [from the supplemental pump]. (8) Opening [from the pump]. (9) Check valve.(10) Flow switch. (11) Opening [to hydraulic tank]. (12) Screen assembly. (13) Check valve.

The flow of oil from the pump flows into opening (8) of the flow control valve. When the enginespeed is between 1050 and 2000 rpm, relief valve (3) and orifice (1) allow approximately 132.5L/min (35 U.S. gpm) of the pump oil to flow through screen assembly (12) to opening (2). This oilflows through check valve (13) into the Hand Metering Unit [HMU]. The pump oil that does notflow to the HMU flows out through opening (11) to the hydraulic tank.

The oil returning from the HMU flows into opening (5) and adds to the pump oil that flows throughopening (11) to the hydraulic tank.

Check valve (13) mounted in opening (2) prevents a reverse flow of oil, which is created by thecylinders during a turn, from returning to the flow control valve from the HMU. Check valve (6)

stops any pump oil flow through opening (7) to the supplemental pump. Check valve (9) mounted inopening (8) prevents a reverse flow of oil to the steering pump.

If the pressure of the pump oil to the HMU reaches approximately 15 100 150 kPa (2190 22 psi),



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relief valve (3) opens. Turn adjustment screw (4) counterclockwise (CCW) if relief valve (3)pressure setting is too high or clockwise (CW) if the pressure setting is too low.

When normal flow loss is sensed by flow switch (10), the supplemental pump begins operating. Theoil from the supplemental pump flows through opening (7), check valve (6), orifice (1), opening (2)and check valve (13) to the HMU. Check valve (9) closes and prevents any oil from flowing throughopening (8) to the pump.

Relief Valve For Cylinders

Relief Valve(A) Port. (B) Port. (1) Valve. (2) Valve.

The relief valve is used to prevent damage from high pressure oil in the cylinder circuit. This occurswhen an outside force on a front wheel suddenly moves a cylinder rod farther in or out of a cylinderthan necessary when the steering wheel is stationary.

When a front wheel strikes against a large object that can not be moved, while the steering wheel is

stationary, the pressure of the oil increases in one end of each cylinder and in the oil lines connectedbetween those ends. This oil pressure increase is also felt through Port A or Port B by valve (1) orvalve (2). If the oil pressure increases to approximately 18 270 kPa (2650 psi), valve (1) or valve (2)will open and allow oil flow to the head ends and rod ends of the low pressure side of the cylinders.



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