TECHNICAL PRESENTATION
320D336D HYDRAULIC EXCAVATORS
-TIER III ENGINES
PILOT HYDRAULIC SYSTEM
Service Training Meeting Guide
(STMG)
TIER III ENGINES
PILOT HYDRAULIC SYSTEM
AUDIENCE
Level II - Service personnel who understand the principles of machine systems operation, diagnostic equipment, and procedures for testing and adjusting.
CONTENT
This presentation provides an introduction and describes the components and systems operation of the 320D-336D pilot hydraulic system. Additional presentations will cover the machine walkaround, engines, pumps and controls, main control valve group, swing system, travel system, and tool control systems in more detail. This presentation may be used for self-paced and self-directed training.
OBJECTIVES
After learning the information in this presentation, the technician will be able to: 1. identify the components and explain the operation of the 320D-336D hydraulic
excavators pilot system, and
2. diagnose problems in the pilot system.
REFERENCES
320D Hydraulic Excavator Specalog AEHQ5856
324D Hydraulic Excavator Specalog AEHQ5663
325D Hydraulic Excavator Specalog AEHQ5665
328D Hydraulic Excavator Specalog AEHQ5706
330D Hydraulic Excavator Specalog AEHQ5667
Machine Monitoring System - Systems Operation RENR8068
Self-study "300D Series Hydraulic Excavators, 345C Hydraulic Excavator,
and 365C & 385C Large Hydraulic Excavators SERV7032
iTIM " '300C' Series Hydraulic Excavators-Electronic Control Systems" SERV2693 iTIM "325C Hydraulic Excavators-Hydraulic Systems" SERV2701
325D Hydraulic Schematic KENR6157
Estimated Time: 45 minutes Illustrations: 19
Form: SERV1852-02 Date: August 2008 © 2008 Caterpillar
TABLE OF CONTENTS
INTRODUCTION ...5
Pilot Manifold ...9
Hydraulic Activation Lever ...14
Pilot Controls and Valves ...16
PREREQUISITES
"Fundamentals of Mobile Hydraulics Self Study Course" TEMV3002 "Fundamentals of Power Train Self Study Course" TEMV3003 "Fundamentals of Electrical Systems Self Study Course" TEMV3004
"Fundamentals of Engines Self Study Course" TEMV3001
NOTES
Nomenclature Change: During the fourth quarter of 2008, the 325D and 330D
nomenclature changed. The 325D became the 329D and the 330D became the 336D for most arrangements.
The exceptions are as follows:
- The nomenclature for the 325D MH and 330D MH did not change. - The nomenclature for the 325D FM and 330D FM did not change.
- The 325D HD HW did not change into 329D HD HW. This model is being discontinued. However, the 330D HD HW changed to the 336D HD HW.
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INTRODUCTION
The oil delivered from the pilot pump performs the following main functions:
- Provides pilot oil pressure to the pilot control valves for implements, swing, and travel in order to perform machine operations.
- Provides pilot pressure oil in order to control the output flows of the main pumps. - Provides pilot pressure oil in order to automatically operate the control devices. The pilot circuit is classified into the following circuits and each circuit performs one of the above functions:
- pilot control valve circuit - power shift pressure system - pressure switch circuits - straight travel valve circuit
- swing parking brake - boom priority
- swing priority - automatic travel speed change
- heavy lift setting of the main relief valve
Stick Cylinder
Bucket Cylinder Boom Cylinders Swing Motor Travel Motors
Pilot Control Valves Priority Valves Main Hydraulic Pumps M Pilot Pump Fan Motor Pilot Manifold
Main Control Valve Group
Fan Pump Tank
The Fan Motor and Pump are only used on the 330D and 336E
This section of the presentation will cover the focus on the pilot manifold, the implement joysticks (pilot valves), and the travel pilot valves.
NOTE: In the fourth quarter of 2008, the 325D and 330D nomenclature changed. The
A gear-type pilot pump (1) provides oil flow to the pilot system. The pilot pump is mechanically connected to the drive pump.
The oil delivery from the pilot pump flows through the pilot oil filter (2) and into the components in the pilot system.
Pilot relief valve (3) is located on the mounting base for the pilot oil filter. The pilot relief valve limits the pressure in the pilot system. The pilot relief valve setting is adjustable. Pilot system pressure can be checked at the test port (4) on the right side of the filter base. Next to the pilot pressure test port is the hydraulic system S•O•S port (5).
2 1 2 3 4 5
3
The filter element in the pilot oil filter removes contaminants from the pilot oil.
If the pilot oil is extremely cold or if the flow of pilot oil through filter element becomes restricted by contaminants, the oil bypasses the filter element through the bypass relief valve. The bypass relief valve is built into the pilot oil filter base.
The pilot oil flows from the pilot pump to inlet port. When the pressure in the pilot oil system reaches the pressure setting of the pilot relief valve, part of the pilot oil flow is returned to the hydraulic tank. The pressure of the pilot system oil in outlet lines is equal to the pressure setting of the pilot relief valve.
Pilot System Relief Valve Pilot System Filter Pilot Filter Relief Valve Pilot System Relief Valve Pilot System Filter Pilot Filter Relief Valve PILOT SYSTEM FILTER
FILTER RELIEF VALVE AND
PILOT SYSTEM RELIEF VALVE
Pilot Manifold
The pilot manifold is the same as the "300C" pilot manifold. The pilot manifold is accessible by removing the cover plate under the machine, behind the swing bearing. The manifold is located directly below the main control valve.
The hydraulic activation valve (1) and solenoid (2) are located in the pilot manifold along with the swing brake solenoid (3) and the two-speed travel solenoid (4).
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1
2 3 4
5
Oil from the pilot pump enters the pilot manifold to be distributed to the various components of the machine. Some of the pilot oil flow is directed to the swing priority valve, to the two speed travel solenoid valve, and to the straight travel solenoid valve. The rest of the pilot oil flows through the check valve.
Two Speed Travel Solenoid Valve: The two speed travel solenoid valve controls oil flow to
the two-speed travel motors. In the illustration above the solenoid is energized. Pilot oil is directed to the travel motors to shift the two displacement change valves (not shown). When the displacement change valves shift, the motors will destroke for higher speed.
Check Valve: The pilot manifold also has a check valve. The check valve maintains pilot
accumulator pressure in the pilot circuit when the engine is not running. By maintaining the pilot pressure (for a limited time) when the engine is stopped, the implements can be lowered safely to the ground.
Swing Priority Valve Swing Brake Solenoid Implement Hydraulic Lockout Solenoid Swing Brake Heavy Lift
Solenoid ValvesPilot
Two Speed Travel Solenoid Hydraulic Activation Valve Pilot Pump Straight Travel Solenoid Travel Motors Check Valve PILOT MANIFOLD
LOCKED - HIGH SPEED TRAVEL
SWING BRAKE ENGAGED Tank
Hydraulic Activation Valve Pilot Pump Hydraulic Activation Valve
Pilot Accumulator: The pilot accumulator is used to release the swing brake and for lowering
the boom and stick in the event of a loss of pilot system pressure or a dead engine. The pilot accumulator also helps to dampen pressure spikes in the pilot system, which enhances the stability of the machine control systems.
The accumulator stores pilot pressure oil for use at the main control valves. During some operations, the pilot system needs more oil because there is insufficient flow from the pilot pump.
Implement Hydraulic Lockout Solenoid Valve and Hydraulic Activation Valve: These two
valves work together to either prevent the implement control valves and the motors from being activated or to allow them to be activated. In the de-energized position, no pilot oil is available to operate the implements. Pilot oil is blocked at both valves.
When the hydraulic lockout control lever in the cab is in or moved to the LOCKED position, the plunger of the limit switch is NOT depressed by the control lever. The limit switch is in the OFF position.
When hydraulic activation control lever is in the LOCKED position, the hydraulic activation solenoid is NOT energized.
The spool is held up by a spring. The spool blocks the pilot supply oil from going to the pilot valves. The spool also opens a passage to drain from the pilot valves to the tank.
In the locked position, if the joysticks are moved, the cylinders and the motors cannot be activated.
Swing Brake Solenoid Valve: The swing brake solenoid valve energizes to release the spring
applied, hydraulically-released, wet disc swing brake. The swing brake is automatically released when any joystick function is performed by the operator.
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When the hydraulic lockout control lever in the cab is placed in the UNLOCKED position, the limit switch closes the circuit path to the lockout solenoid valve. The lockout solenoid valve is energized.
When the implement hydraulic lockout solenoid valve is energized, pilot oil is directed to move the hydraulic activation valve down. Pilot oil flows through the hydraulic activation valve to the swing brake solenoid valve, the left and right joysticks (pilot valves), and the travel pilot valves. The hydraulic activation valve also supplies pilot oil for the heavy lift solenoid valve. When an implement is activated the swing brake solenoid is energized by the Machine ECM. Pilot oil is directed through the swing brake solenoid valve to release the swing park brake in the swing motor group.
Swing Priority Valve Swing Brake Solenoid Implement Hydraulic Lockout Solenoid Swing Brake Heavy Lift Solenoid ValvesPilot Two Speed Travel Solenoid Hydraulic Activation Valve Pilot Pump Straight Travel Solenoid Travel Motors Check Valve PILOT MANIFOLD
UNLOCKED - SWING BRAKE RELEASED Tank
Hydraulic Activation Valve Pilot Pump Hydraulic Activation Valve Implement Hydraulic Lockout Solenoid
The pilot accumulator (arrow) provides pressure oil to the pilot system when the pilot pump flow is low or the pilot pump has stopped.
Low pilot oil flow to the pilot system may be caused by the following two reasons:
- Implements are lowered while the engine is stopped and oil supply to the main control valves is stopped.
- Combined implement, swing, and travel operations.
Hydraulic Activation Lever
The hydraulic lockout lever (arrow) is shown in the LOCKED position.
The engine will not start unless the hydraulic activation lever (3) is in the LOCKED position. Raise the lever activation lever to the UNLOCKED position to energize the implement
hydraulic lockout solenoid valve to allow the operator to move the implements.
If the machine is running, the operator can lockout the implement controls by returning the lever to the LOCKED position.
HYDRAULIC ACTIVATION LEVER Limit Switch Plunger Lever Hydraulic Activation Lever
A limit switch and plunger are located on a bracket with the hydraulic lockout lever. When the hydraulic activation control lever is moved forward, the lever pushes the plunger down to activate the limit switch.
When the hydraulic lockout control lever is shifted to the rear to the LOCKED position, the implement lockout solenoid valve is NOT energized, so the hydraulic activation valve does NOT shift to direct pilot oil to the pilot control valves.
The joysticks and/or travel pedals can NOT shift a control valve in the main control valve group when the hydraulic activation lever is in the LOCKED position.
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Pilot Controls and Valves
Pilot controls in the cab include: - left (1) and right (2) travel pedals - left (3) and right (4) travel levers - auxiliary foot switch (5) (attachment) - straight travel (6) (attachment)
- left joystick (7) to control the swing and stick (SAE excavator pattern) - right joystick (8) to control the bucket and boom (SAE excavator pattern) - foot rest (9 and 10)
The joysticks shown above are equipped with full electronic control for the tool control system.
NOTE: The switch for one touch low idle is on the right joystick. If the machine is
equipped with a magnet, the trigger switch on the front of the right joystick turns the magnet on, while the trigger switch on the front of the left joystick turns the magnet off.
1 2 3 4 5 6 7 8 9 10
The resolver block (1) is located under the cab. The resolver block provides a junction between the pilot lines to the joysticks and the pilot lines to the main control valve group as well as sensing when an an implement or the swing is activated.
The resolver network in the block, directs the pilot signal pressure to the swing/implement pressure switch (2) for Automatic Engine Control (AEC).
Two travel pressure switches (not shown) and the swing/implement pressure switch (2) are activated by pilot pressure oil. The switches close at 490 ± 49 kPa (71 ± 7 psi) and open at 290 ± 0 kPa (42 ± 0 psi).
The pressure switches are inputs to the Machine ECM. The Machine ECM uses these inputs to determine when a hydraulic function has been activated.
If Automatic Engine Control (AEC)/one touch low idle is activated and the machine is at low idle the Machine ECM and will increase the engine speed to the current speed dial setting. When only the swing/implement pressure switch is activated, the Machine ECM will release the swing brake. When all three pressure switches are activated at the same time, the Machine ECM will energize the straight travel solenoid.
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1
12
When one or more of the joysticks are shifted, resolvers in the block direct the highest pilot oil pressure to the the swing/implement pressure switch.
The Machine ECM will cause the engine to increase rpm to match the speed dial position.
Bucket Boom Stick Swing
OUT IN R L OPEN CLOSE DOWN UP
bR3 bR4 aR4 aR3 bL3 bL2 bL4 aL2
IMPLEMENT PILOT
JOYSTICKS
Resolver Block Swing/Implement Pressure SwitchTravel Pilot Valves Travel Pilot Valves
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When the pilot joystick lever is shifted, the joystick contacts the plunger and pushes the plunger down against its spring. The plunger will contact the spool and move the spool down against its spring. Depending on how far the joystick lever is moved, determines how far the spool moves.
As the spool moves down, the spool will close off the drain passage for the oil to the control valve and meter pilot pressure oil to the control valve to cause the control spool (not shown) to shift. The greater the pilot oil flow to the control spool, the greater the control spool travel. As pressure increases in the pilot line to the control valve, the pressure moves the spool up to a balance position against the spool and metering springs to maintain a constant pilot pressure in the pilot line. This action will maintain the control spool position in the control valve until the joystick is moved.
In summary, once the pilot joystick is shifted, the pilot valve becomes a pressure reducing valve which maintains a downstream pressure equal to the spring forces above the spool.
When the joystick is released, the joystick will return to the NEUTRAL position due to the force of the return spring moving the spool up. When this action occurs, the pilot oil is blocked by the spool from flowing to the control valve to shift the control spool. Pilot oil at the control spool is drained to the tank past the spool.
Joystick Plunger Return Spring Seat Return Chamber SECTION A-A Plate Supply Pilot Oil Port A Port B Metering Spring Spool A A Pilot Manifold Pilot Manifold Port A Port B
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The travel pilot control valve operates similar as the implement pilot valves.
Depending on how far the the travel pedal or lever is moved, will determine the amount of pilot oil directed to the respective travel control valve.
A dampening function is built into the travel pilot control valve which allows the operational speed of the travel lever/pedal to respond only to intended movements of the operators foot. The dampening function also prevents vibration or harshness when releasing the travel pedal. When the travel lever/pedal is moved suddenly from the NEUTRAL position, the rod is pushed downward. The rod moves the dampening piston downward. The hydraulic oil below the dampening piston is pressurized.
An orifice check valve allows the trapped hydraulic oil below the dampening piston to gradually flow into into the metering spring chamber, which is open to the tank. The gradual flow of oil through the orifice check valve provides the dampening function.
aL1 bL1 bR1 aR1 Pilot Supply Dampening
Piston
Travel Pressure
Switch (AEC) Resolver
TRAVEL PILOT CONTROL VALVE
Pedal
Pilot Supply
Travel
Valve Travel Valve
Rod Spool Metering Spring Tank Dampening
Piston Orifice Check Valve
Return Spring
REV FWD FWD REV
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The attachment circuits are controlled by proportional solenoids valves. These valves are also called proportional reducing valve or PRV. The valves receive PWM signals from the Machine ECM to shift energize the solenoid. The amount of current sent from the Machine ECM will determine how far the solenoid spool shifts.
As the solenoid spool shifts, pilot oil is metered from one of the energized solenoid valves to the attachment circuit to control the position of the control spool for the attachment.
When the solenoid is de-energized the solenoid spool shifts to block the pilot oil. The pilot supply passage to the control spool is open to the tank.
NOTE: The solenoid valves also act as variable pressure reducing valves. Instead of
using a spring to control the downstream pressure, the current is varied to the solenoid to control the downstream pressure to the control spool. For a fixed current the pilot pressure to the spool is maintained as it was for the joysticks.
Solenoid Spring
Pilot Oil Tank Control Spool
PWM SIGNAL INCREASE PWM SIGNAL DECREASE
Spring Pilot Oil Tank Plunger Control Spool PWM SOLENOID VALVE
When the joysticks are operated, the pilot control valves send pilot pump oil through the pilot lines to the pilot ports (arrows) at the main control valve group in order to shift the spools in the main control valve.
Additional pilot lines are located below the main control to shift the control spools in the opposite direction.
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Pilot oil enters a control valve from either end to shift the main control spool.
The control spool will shift in proportion to the amount of pilot oil sent to the control spool from the a pilot valve or solenoid.
For some circuits, proportional solenoid valves are used to direct pilot oil to shift the control spool. Center Bypass Passage Parallel Feeder Passage Load Check Valve
CONTROL VALVE
FULL SHIFT Port A Port B Pilot Valve or Solenoid Passage to Next Valve Line Relief andCONCLUSION
This presentation has provided information for the Caterpillar 320D-336D Hydraulic Excavators.
This presentation covered the pilot control system and pilot control valves. Additional presentations are available for each system used on these machines.
When used in conjunction with the service manual, the information in this package should permit the technician to do a thorough job of analyzing a problem in these systems. For service repairs, adjustments, and maintenance, always refer to the Operation and Maintenance Manual, Service Manuals, and other related service publications.
