789D Off-Highway Truck: Metering Pump (Steering)

Location of steering metering pump

The steering metering pump is located on the base of the steering column under a cover at the front of the cab. The resilient mounting of the metering pump will prevent vibration damage and noise.

Steering metering pump NEUTRAL position (1) Inner spool (2) Drain outlet to tank (3) Left turn port (4) Outer sleeve (5) Right turn port (6) Inlet (7) Passage (8) Stator (9) Rotor (10) Passage (11) Drive (12) Pin (13) Centering springs (A) Control section(B) Metering section

The steering metering pump is made up of the following two sections:

• Control section (A)
• Metering section (B)

The two sections are connected by hydraulics and by mechanics.

Pump oil from the steering control valve goes through inlet (6) into control section (A). When the steering wheel is turned, control section (A) sends oil to metering section (B). Metering section (B) produces a specific amount of oil flow. Metered oil from metering section (B) is then directed by control section (A) to either left turn port (3) or right turn port (5). This oil becomes pilot oil for the steering control valve. As the steering wheel is turned faster, there is an increase in the flow of pilot oil. The steering cylinders will move farther with increased speed.

Oil Flow

Control section (A) of the steering metering pump is a closed center type. When the steering wheel is in the NO STEER position, there is no alignment between the holes in sleeve (4) and the passages in spool (1). However, a small amount of pump oil from inlet (6) is allowed to flow through the center position of the steering metering pump. This small amount of oil flow (thermal bleed) keeps the steering metering pump full. This will give a response time that is quick to steering demands. The thermal bleed also helps keep the pilot oil lines to the steering control valve and the steering metering pump warmed during cold weather operations.

Right Turn

Steering metering pump Right turn (1) Inner spool (4) Outer sleeve (5) Right turn port (6) Inlet (7) Passage (8) Stator (9) Rotor (10) Passage (11) Drive (12) Pin (13) Centering springs (A) Control section(B) Metering section

Spool and sleeve (1) Inner spool (4) Outer sleeve (14) Holes for pin (12) (15) Small holes for oil flow (16) Grooves for oil flow(17) Slots for centering springs

When the steering wheel is turned clockwise, spool (1), pin (12) and drive (11) start to turn. Sleeve (4) will not turn because spool (1) will turn inside sleeve (4). Small holes (15) in sleeve (4) will be in line with grooves (16) in spool (1). The thermal bleed is blocked when spool (1) and sleeve (4) rotate.

Pump oil from inlet (6) goes through small holes (15) in sleeve (4) into grooves (16) in spool (1). The oil in grooves (16) goes out through other small holes (15) in sleeve (4) and into passage (10). Oil flows through passage (10) into metering section (B). Then, the oil is directed into a space between stator (8) and rotor (9) .

Rotor (9) is splined to drive (11). As drive (11) turns, rotor (9) pumps oil through passage (7). The metered oil flows back into sleeve (4) through small holes (15) and into other grooves (16) in spool (1). This oil then leaves sleeve (4) through small holes (15). Then, the oil flows into right turn port (5). Pilot oil from port (5) goes to the directional spool in the steering control valve.

When the steering wheel is not turned, spool (1), pin (12), drive (11) and rotor (9) will not turn. Centering springs (13) will bring spool (1) and sleeve (4) back to the NEUTRAL position. Small holes (15) in sleeve (4) are not in alignment with grooves (16) in spool (1). Metered oil to right turn port (5) stops. This causes the wheels to stay in the current position.

Left Turn

Steering metering pump Left turn (1) Inner spool (3) Left turn port (4) Outer sleeve (6) Inlet (7) Passage (8) Stator (9) Rotor (10) Passage (11) Drive (12) Pin (13) Centering springs (A) Control section(B) Metering section

The operation is in the opposite direction. When the steering wheel is turned counterclockwise for a left hand turn, spool (1), pin (12) and drive (11) start to turn. Oil comes in inlet (6). Since spool (1) and sleeve (4) are turned, a different set of holes and grooves will line up. Oil flows through spool (1) and sleeve (4) into passage (7) and metering section (B). Metered oil flows through passage (10), spool (1) and sleeve (4), and out left turn port (3). Pilot oil goes to the steering control valve.

Pump gears in metering section (B) (8) Stator (9) Rotor (11) Drive(12) Pin

If the steering metering pump is disassembled, assemble the steering metering pump with the proper relationship between rotor (9) and pin (12). Use Illustration 6 for reference. Erratic steering will result if Illustration 6 is not used as a guide.

Load Sensing

The steering metering pump has a load sensing port. The load sensing port is connected to inlet (6) through an orifice. Oil pressure in inlet (6) is felt in the load sensing line. This signal pressure is communicated to the priority spool in the steering control valve. Refer to Systems Operation, "Steering Control Valve" for a more complete explanation on the operation of the steering metering pump and the steering control valve.

MARYGAR

789D Off-Highway Truck: Metering Pump (Steering) 2012-12-12T19:28:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown