Steering System

Reference: For Specifications with illustrations, refer to the Specifications for the CB-534 Steering System, Form No. KENR2418. If the Specifications in Form No. KENR2418 are not the same as listed in the Systems Operation and the Testing And Adjusting, look at the print date on the back cover of each book. Use the Specifications listed in the book with the latest date.

Steering System Schematic
(1) Hydraulic tank. (2) Filter. (3) Return line. (4) Right turn line. (5) Steering cylinders. (6) Suction line. (7) Steering pump. (8) Steering control unit (SCU). (9) Left turn line.

The steering system is a hydrostatic system. The steering is controlled completely through hydraulics. The main components of the steering system are hydraulic tank (1), steering pump (7), steering control unit (8) and steering cylinders (5).

Hydraulic Tank Location
(1) Hydraulic tank. (2) Filter. (6) Suction line.

Hydraulic tank (1) provides oil for the steering, propulsion and vibration systems. Oil in the tank is cleaned by filter (2). The filter is mounted to the hydraulic tank and is connected to suction line (6).

Oil from hydraulic tank (1) is sent into the steering circuit by gear-type pump (7). The steering pump drive, which is part of the engine front timing gear group, drives the steering pump.

Steering Control Unit Location
(8) Steering control unit. (10) Steering column base support.

Steering control unit (SCU) (8) is located at the bottom of the steering column just under base support (10).

The SCU is an open center, no reaction type. When the steering wheel is not turned the open center ensures a free passage of oil between pump (7) and tank (1).

The right and left turn ports do not sense each other's oil flow. This will give an absence of reaction on the steering wheel. This will maintain the original turn position of the drums.

SCU Schematic (Steering Wheel Not Turned)
(L) Left turn line. (P) Inlet line from pump. (R) Right turn line. (T) Return line to tank.

SCU (8) will give manual steering if the oil flow from the pump fails. The SCU automatically functions as a handpump and emergency steering of the compactor is maintained.

Steering Cylinder Location
(5) Steering cylinders (left side shown).

When the steering wheel is turned, two double acting hydraulic cylinders (5), receive oil from SCU (8) so that the compactor can make the desired turn. When the steering wheel is not being turned, oil goes through SCU (8) and back to tank (1).

Steering Pump

Steering Pump
(1) Splined sleeve. (2) Drive gear shaft. (3) Drive gear. (4) Body. (5) Rear cover. (6) Drive shaft. (7) Front cover. (8) Passage. (9) Front wear plate. (10) Driven gear. (11) Rear wear plate. (12) Driven gear shaft.

The steering pump is a gear-type pump driven by a drive that is part of the engine front timing gear group. The pump turns clockwise when the engine is running.

Oil is drawn into the pump through suction port (15) by gears (3) and (10).

Oil circulates around the gears and is sent out through discharge port (13) towards the SCU.

Oil Flow Through Pump
(13) Discharge port. (14) Pressure zone. (15) Suction port. (16) Passage.

Oil from the discharge line feeds pressure zone (14). The purpose of this high pressure is to push the wear plates against the gears thus eliminating axial play.

Internal leakage is returned to suction port (15) through passage (8).

Steering Control Unit (SCU)

Steering Control Unit (SCU) (Top View)
(1) Inlet port. (2) Right turn port. (3) Outlet port. (4) Left turn port.

Steering Control Unit (SCU-Side View)
(1) Inlet port. (3) Outlet port. (5) Passage. (6) Passage. (7) Spool. (8) Centering springs. (9) Drive shaft. (10) Cross pin. (11) Gerotor. (12) Gear rim. (13) Passage. (14) Sleeve. (15) Housing. (A) Control section. (B) Pump section.

The steering control unit (SCU) has two main sections. They are control section (A) and pump section (B). These two sections work together to send oil to the steering cylinders.

The direction and the speed of a turn are controlled by the SCU. As the steering wheel is turned faster, there is an increase in the flow of oil to the steering cylinders. This increased flow causes the cylinders to move farther and faster, which turns the machine faster.

Neutral Position

SCU In Neutral Position
(16) Steering cylinders. (17) Relief valve. (18) Suction valve. (19) Steering pump. (A) Control section. (B) Pump section.

When the steering wheel is not being turned, the steering control unit is in the NEUTRAL position. Oil from the pump enters the SCU through inlet (1) and passage (6). Since the SCU is open-centered, a passage is open through sleeve (14) and spool (7) which allows the oil flow to go through to outlet port (3) and back to the tank.

Right Turn

SCU In Right And Left Turn Positions
(16) Steering cylinders. (17) Relief valve. (18) Suction valve. (19) Steering pump. (A) Control section. (B) Pump section.

When the steering wheel is turned for a right turn, oil from pump (19) flows into the SCU through inlet (1) and passage (6). From passage (6) it goes into the gerotor through passage (13). With the steering wheel turning, gerotor (11) is turning and pumping oil. The oil flow comes out through passage (5), where it is directed to the steering cylinders through right turn port (2)

Spool And Sleeve
(7) Spool. (14) Sleeve. (20) Slots for springs. (21) Holes for pin. (22) Small holes for oil flow. (23) Grooves for oil flow.

When the steering wheel starts to turn, spool (7), pin (10) and drive shaft (9) also start to turn. Sleeve (14) does not start to turn at the same time as the spool because the diameter of holes (21) in the sleeve are slightly larger than the diameter of pin (10). This allows spool (7) to turn inside of sleeve (14) enough to put small hole (22) in sleeve (14) in line with grooves (23) in spool (7). The alignment of these holes and grooves provides the path for oil flow to gerotor (11) and to the steering cylinders. Centering springs (8) are compressed when the spool moves in relation to the sleeve. When the steering wheel is no longer turning, the springs will bring the spool and sleeve back to a neutral position.

This means that the drums will stay in the position they were in when the steering effort stopped. The steering wheel must be turned in the opposite direction to bring the drums back to straight ahead, or to make a left turn. As the oil goes out to the cylinders through port (2) for a right turn, return oil from the cylinders is coming back into the SCU through left turn port (4). This oil is sent back to the tank through outlet port (3).

Left Turn

When the steering wheel is turned to the left, the same components move that do for a right turn, only in the opposite direction. The oil flow through the SCU is also in the opposite direction to that of a right turn. Oil still comes in at inlet port (1) and passage (6) but then goes to gerotor (11) through passage (5). From gerotor (11) the oil leaves through passage (13) and goes through the sleeve and spool to left turn port (4). From port (4) the oil goes to the steering cylinders.

The oil volume supplied to the cylinders is proportional to the angular rotation of the steering wheel.

Steering Control Unit (SCU) Valves

Steering System Circuit
(16) Steering cylinders. (17) Relief valve. (18) Suction valve. (19) Steering pump. (24) Suction line. (25) Filter. (26) Tank. (27) Left turn line. (28) Steering control unit (SCU). (29) Passage. (30) Shock valves. (31) Passage. (32) Tank return line. (33) Right turn line. (34) Anti-cavitation valves.

Shock Valve
(35) Plug. (36) Setting screw. (37) Spring. (38) Valve cone. (39) Ball.

The SCU has its own built-in valve groups. Two direct acting type shock valves (30), calibrated at 20 000 kPa (2900 psi), cushion sudden high pressure increases caused by shocks on the steered drums. They protect the working lines and prevent damage to the steering system. The valves, which are hydraulically piloted, react very quickly. This allows oil which has been submitted to a sudden shock in working lines (27) and (33) to pass through valves (30). The oil then flows into the SCU and out through outlet port (3) and to the tank.

Anti-Cavitation Valve
(40) Ball. (41) Screw.

Two anti-cavitation valves make sure there is oil suction to the chambers of the steering cylinders. Without these valves, cavitation could occur during poor steering conditions.

These valves work in conjunction with the shock valves. Whenever one working line is submitted to a sudden shock, the corresponding anti-cavitation valve on the same line will be closed. At the same time, the anti-cavitation valve on the opposed working line will open due to the displacement of the hydraulic cylinder piston. Suction created by the movement of the cylinder piston will cause ball (40) to move. Oil will be drawn into the SCU from the tank return line through passage (31) and out into the working line through passage (29) thus preventing cavitation.

Pressure Relief Valve
(42) Valve seat. (43) Piston. (44) Spring. (45) Setting screw. (46) Plug.

Pressure relief valve (17) limits the maximum pressure drop across the SCU to protect the steering system. In addition the valve makes sure there is bypass oil from the delivery line into the tank return line when the steering cylinders are at their stops. The valve is set at 14 000 kPa (2050 psi).

Inlet Port Check Valve And Suction Valve
(1) Inlet port. (3) Outlet port. (47) Inlet port check valve. (48) Screw. (49) Guide bushing. (50) Ball.

Check valve (47) in inlet port (1) prevents oil from returning through the SCU when pressure on the cylinder side is greater than pressure on the pump side. This prevents sudden movement of the steering wheel when the machine is first started. The check valve opens at a minimum pressure of 110 kPa (16 psi).

If there is an operating fault before the SCU, such as a broken oil line, pump or engine failure, a suction valve allows the SCU to automatically convert to a manual emergency pump.

When the steering wheel is turned for a right or left hand turn, the SCU will draw oil from the tank return line through port (3). This will cause valve ball (50) to move and allow oil to pass into feed line passage (6). Oil is then sent through the SCU and out to the cylinders.