336D MHPU Mobile Hydraulic Power Unit Hydraulic System Combined Function Hydraulic System - System 18 Caterpillar

Illustration 1	g01892095
(1) Machine ECM (8) Line for work tool (9) Line for work tool (10) Number two line relief valve (11) Pressure sensor (12) Number one line relief valve (14) Extend solenoid for attachment stem 1 (15) Retract solenoid for the attachment stem 1 (16) Extend solenoid for the attachment stem 2 (17) Retract solenoid for the attachment stem 2 (18) Proportional solenoid valve for negative flow control (19) Relief valve (line) (20) Auxiliary control valve (21) Attachment control valve (23) Main control valve (24) Joystick (right) (25) Joystick (left) (26) Pilot manifold (27) Hydraulic tank (29) Idler pump (30) Drive pump (31) Pilot pump

System 18 is designed to allow complete electronic control over the tool control system. The combined function hydraulic system that is present on excavators that are equipped with a System 18 combines the features of the one-way/two-way flow system with the features of the one pump/two pump flow system.

The one pump flow system allows flow from one pump to power a work tool. All of the load is placed on a single pump. One pump flow is used for work tools that require low flow rates for actuation.

The two pump flow system allows the combined flow from both pumps to power a work tool. Rather than placing all of the load on a single pump, the two pump flow system allows the two pumps to provide flow equally. Two pump flow is used for work tools that require high flow rates for actuation. Two pump flow distributes the load equally for work tools that are used extensively.

Refer to Table 1 for the appropriate work tool and "TOOL#".

Two joystick thumb wheels are used to operate the work tool.

Illustration 2	g01195826
(32) Horn (33) Left joystick (34) Left joystick thumb wheel (35) Right joystick (36) Right joystick thumb wheel (37) Switch for one-way flow (38) One touch low idle

One-Way Flow from One Pump

Illustration 3	g01892284

Description

The default parameter values for one-way hydraulic oil flow from one main pump are shown in Table 1. A typical example is a hammer. Refer to Testing and Adjusting, "System 18: Default Value of Work Tool Parameters" for the Tool Control System.

Use the display monitor or ET in order to set the hydraulic flow to the work tool.

The work tool is operated by switch (37) that is located on the right joystick (35).

Operation

Pilot pump (31) supplies oil to pilot manifold (26). When the hydraulic activation lever is moved to the UNLOCK position, pilot oil flows from pilot manifold (26) to solenoid valves: (14), (15), (16) and (17) .

When switch (37) is pressed, the machine ECM sends a signal to the extend solenoid for attachment control valve (14). Pilot oil flows to attachment control valve (21). The pilot oil will shift the spool in attachment control valve (21) to the DOWNWARD position. This allows oil from drive pump (30) to flow through the valve. The pump oil flows through the line for the work tool (9) to the work tool. Return oil flows through the line for the work tool (8) and back to hydraulic tank (27) .

During operation of the work tool, the machine ECM sends a signal to the proportional solenoid valve for negative flow control (18). Negative flow control pressure in the center bypass passage is blocked when the control valve spools shift DOWNWARD. The machines ECM has the following programmed parameter values: "A1 FLOW", "A1 MULTI ADD FLOW", "A1 NOMINAL PRES" and "COMBINER ENABLE". The parameters control the flow and pressure of the work tool. The machine ECM regulates the negative flow control pressure that will be supplied to the pump regulator. The negative flow control pressure forces the swashplate in the pump to the correct angle to limit the flow and pressure to the work tool.

One-Way Flow from Two Pumps

Illustration 4	g01892288

Description

The default parameter values for one-way hydraulic oil flow from two main pumps are shown in Table 1. A typical example is a hammer. Refer to Testing and Adjusting, "System 18: Default Value of Work Tool Parameters" for the Tool Control System.

Use the display monitor or ET in order to set the hydraulic flow to the work tool.

The work tool is operated by switch (37) that is located on right joystick (35) .

Operation

Pilot pump (31) supplies oil to pilot manifold (26). When the hydraulic activation lever is moved to the UNLOCK position, pilot oil flows from pilot manifold (26) to solenoid valves: (14), (15), (16) and (17) .

When switch (37) on the right joystick is pressed, the machine ECM sends a signal to the extend solenoid for attachment control valve (14) and the extend solenoid for auxiliary control valve (16).

Pilot oil flows to attachment control valve (21) and to auxiliary control valve (20). The pilot oil will shift the control valve spools DOWNWARD. This allows oil from drive pump (30) to flow through attachment control valve (21) and this allows oil from idler pump (29) to flow through auxiliary control valve (20). Hydraulic oil from the two pumps combines after the oil passes through both valves. The pump oil flows through the line for the work tool (9) to the work tool. Return oil flows through the line for the work tool (8) and back to hydraulic tank (27) .

During operation of the work tool, the machine ECM sends a signal to the proportional solenoid valve for negative flow control (18). Negative flow control pressure in the center bypass passage is blocked when the control valve spools shift DOWNWARD. The machines ECM has the following programmed parameter values: "A1 FLOW", "A1 MULTI ADD FLOW", "A1 NOMINAL PRES" and "COMBINER ENABLE". The parameters control the flow and pressure for the work tool. The machine ECM regulates the negative flow control pressure that will be supplied to the pump regulator. The negative flow control pressure forces the swashplate in the pump to the correct angle to limit the flow and pressure to the work tool.

Two-Way Flow from One Pump

Illustration 5	g01892389

Illustration 6	g01892395

Description

The default parameter values for two-way hydraulic oil flow from one main pump are shown in Table 1. A typical example is a pulverizer. Refer to Testing and Adjusting, "System 18: Default Value of Work Tool Parameters" for the Tool Control System.

Use the display monitor or ET in order to set the hydraulic flow to the work tool.

The "TOOL#" determines the control device that operates the work tool. The work tool operates with modulated control from the right joystick thumb wheel. The work tool can be rotated by operating the left joystick thumb wheel.

Operation

When the hydraulic activation lever is moved to the UNLOCK position, pilot pump (31) supplies oil to solenoid valves: (14), (15), (16) and (17). When right joystick thumb wheel (36) is moved FORWARD, the machine ECM sends a signal to the extend solenoid for attachment control valve (14). Pilot oil flows to the top of attachment control valve (21). The pilot oil will shift the spool to the DOWNWARD position. This allows oil from drive pump (30) to flow through attachment control valve (21). The pump oil flows through the line for the work tool (9) to the work tool. Return oil flows through the line for the work tool (8) and back to hydraulic tank (27) .

When right joystick thumb wheel (36) is moved BACKWARD, the machine ECM sends a signal to the retract solenoid for attachment control valve (15). Pilot oil flows to the bottom of attachment control valve (21). The pilot oil will shift the spool to the UPWARD position. This allows oil from drive pump (30) to flow through attachment control valve (21). The pump oil flows through the line for the work tool (8) to the work tool. Return oil flows through the line for the work tool (9) and back to hydraulic tank (27) .

The work tools pressure setting is regulated by relief valve (12) and relief valve (10). The machine ECM sends a signal to the line relief valves. The signal adjusts the pressure according to the set parameter. To view the parameters for the work tool, refer to Testing and Adjusting, "System 18: Default Value of Work Tool Parameters" for the Tool Control System.

During operation of the work tool, the machine ECM sends a signal to the proportional solenoid valve for negative flow control (18). Negative flow control pressure in the center bypass passage is blocked when the control valve spools shift DOWNWARD. The machine ECM has the following programmed parameter values: "A1 FLOW", "A1 MULTI ADD FLOW", "A1 NOMINAL PRES" and "COMBINER ENABLE". The parameters control the flow and pressure for the work tool. The machine ECM regulates the negative flow control pressure that will be supplied to the pump regulator. The negative flow control pressure forces the swashplate in the pump to the correct angle to limit the flow and pressure to the work tool.

Two-Way Flow from Two Pumps

Illustration 7	g01892414

Illustration 8	g01892415

Description

The default parameter values for two-way hydraulic oil flow from two main pumps are shown in Table 1. A typical example is a pulverizer. Refer to Testing and Adjusting, "System 18: Default Value of Work Tool Parameters" for the Tool Control System.

The work tool is operated by right joystick slide control (36) .

Note: Refer to Testing and Adjusting, "System 18: Default Value of Work Tool Parameters" and Testing and Adjusting, "Work Tool Parameter - Program" for the Tool Control System.

Operation

Pilot pump (31) supplies oil to pilot manifold (26). When the hydraulic activation lever is moved to the UNLOCK position, pilot oil flows from pilot manifold (26) to the solenoid valves: (14), (15), (16) and (17) .

When right joystick thumb wheel (36) is moved FORWARD, the machine ECM sends a signal to the extend solenoid for attachment control valve (14) and the extend solenoid for auxiliary control valve (16). The signal is proportional to the forward displacement of the joystick thumb wheel. Pilot oil flows to the top of attachment control valve (21) and auxiliary control valve (20). The pilot oil will shift the spool in each control valve DOWNWARD. This allows oil from drive pump (30) to flow through attachment control valve (21) and this also allows oil from idler pump (29) to flow through auxiliary control valve (20). The hydraulic oil from the two pumps combines after the oil passes through both valves. The pump oil flows through the line for the work tool (9) to the work tool. Return oil flows through the line for the work tool (8) and back to hydraulic tank (27) .

When right joystick thumb wheel (36) is moved BACKWARD, the machine ECM sends a signal to the retract solenoid for attachment control valve (15) and the retract solenoid for auxiliary control valve (17). Pilot oil flows to the bottom of attachment control valve (21) and auxiliary control valve (20). The pilot oil will shift the spool in each control valve UPWARD. This allows oil from drive pump (30) to flow through attachment control valve (21) and this also allows oil from idler pump (29) to flow through auxiliary control valve (20). The hydraulic oil from the two pumps combines after the oil passes through both valves. The pump oil flows through the line for the work tool (8) to the work tool. Return oil flows through the line for the work tool (9) and back to hydraulic tank (27) .

The work tools pressure setting is regulated by relief valve (12) and relief valve (10). The machine ECM sends a signal to the line relief valves. The signal adjusts the pressure according to the set parameter. To view the parameters for the work tool, refer to Testing and Adjusting, "System 18: Default Value of Work Tool Parameters" for the Tool Control System.

During operation of the work tool, the machine ECM sends a signal to the proportional solenoid valve for negative flow control (18). Negative flow control pressure in the center bypass passage is blocked when the control valve spools shift DOWNWARD. The machine ECM has the following programmed parameter values: "A1 FLOW", "A1 MULTI ADD FLOW", "A1 NOMINAL PRES" and "COMBINER ENABLE". The parameters control the flow and pressure for the work tool. The machine ECM regulates the negative flow control pressure that will be supplied to the pump regulator. The negative flow control pressure forces the swashplate in the pump to the correct angle to limit the flow and pressure to the work tool.

Clench Pressure

Some work tools grip objects in order to move the objects. Machines that are equipped with System 18 can grip objects without crushing or dropping the objects when the clench pressure is set correctly. Parameter "F2 DERATE MAX PRES" is used with parameters "F2 SQEZ START PRES", "F2 SQEZ END PRES" and "A1 EXTEND MAX PRES" in order to control the clench pressure.

Parameter "F2 DERATE MAX PRES" is set to a value for the pilot pressure that is less than parameter "A1 EXTEND MAX PRES". Parameter "F2 SQEZ START PRES" is used in order to control the lower limit of the range for the clench pressure. Parameter "F2 SQEZ END PRES" is used in order to control the upper limit for the clench pressure. Parameter "A1 EXTEND MAX PRES" is used in order to control the maximum pilot pressure.

The electronic control system uses a pressure sensor in order to monitor the hydraulic pressure in the head end of the work tool cylinders. When the pressure that is detected by this sensor falls between the upper and lower limits, the electronic control system reduces the pilot pressure that is used to activate the circuit.

Illustration 9	g01296093

When the clench pressure circuit is activated in order to grip an object, the hydraulic pressure for the work tool circuit increases to the line relief setting. As the circuit pressure increases, the electronic control system monitors the head end pressure of the work tool cylinder. When the head end pressure reaches the value of parameter "F2 SQEZ START PRES", the electronic control system begins lowering the pilot pressure. The pilot pressure is reduced to the value of parameter "F2 DERATE MAX PRES" before the hydraulic pressure on the head end of the work tool cylinder reaches the value of parameter "F2 SQEZ END PRES".