Cfm56 7 b hydromechanical unit

CFMI Proprietary InformationGEK-112940

PRELIMINARY ISSUE

CFM56-7B Hydromechanical UnitTraining Manual

Customer Training ServicesAugust 2000

CFM56-7BHYDROMECHANICAL UNIT

TRAINING MANUAL

Document: GEK-112940Revised: Aug. 2000Published by CFMI

CFMI Customer Training CenterGE Aircraft EnginesCustomer Technical Education Center123 Merchant StreetMail Drop Y2Cincinnati, Ohio 45246USA

CFMI Customer Training Center SNECMA (RXEF)Direction de l’Après-Vente CivileMELUN-MONTEREAUAérodrome de Villaroche B.P. 193677019 - MELUN-MONTEREAU CedexFRANCE

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EFFECTIVITYB737-600, -700, -800, -900, -BBJ, COMBI, C40A/ALL

CFMI PROPRIETARY INFORMATION

CFM56-7B TRAINING MANUAL

THIS PAGE INTENTIONALLY LEFT BLANK

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This CFMI publication is for Training Purposes Only . The information is accurate at the time of compilation; however, no update service will be furnished to maintain accuracy. For authorized maintenance practices and specifications, consult pertinent maintenance publications.

The information (including technical data) contained in this document is the property of CFM International (GE and SNECMA). It is disclosed in confidence, and the technical data therein is exported under a U.S. Government license. Therefore, None of the information may be disclosed to other than the recipient.

In addition, the technical data therein and the direct product of those data, may not be diverted, transferred, re-exported or disclosed in any manner not provided for by the license without prior written approval of both the U.S. Government and CFM International.

COPYRIGHT 2000 CFM INTERNATIONAL

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Table of ContentsTopic Revision Page Numbers

Table of Contents Aug. 2000 5Acronyms and Abbreviations Aug. 2000 7-12Hydromechanical Unit Course Objectives Aug. 2000 13

- HMU External Views Aug. 2000 14-23

- Pressurizing and Shutoff Valve Aug. 2000 24-25

- Electro-Hydraulic Servo Valves (EHSV’S) Aug. 2000 26-33

- Shutoff Shutter Valve Aug. 2000 34-35

- Head Sensor Aug. 2000 36-37

- Bypass Valve Aug. 2000 38-39

- Pressure Regulators (Pc and Pcr) Aug. 2000 40-41

- Overspeed Governor Aug. 2000 42-45

- Burner Staging Valve (BSV) Aug. 2000 46-47

- Airframe Shutoff Valve Aug. 2000 48-49

- Fuel Metering Valve and System Schematic Aug. 2000 50-51

- HMU System Schematics Aug. 2000 52-60

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ABBREVIATIONS & ACRONYMS

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Aac Alternating CurrentA/C AircraftACARS Aircraft Communication Addressing and

Reporting SystemADEPT Airline Data Engine Performance TrendADIRU Air Data and Inertial Reference UnitAGB Accessory GearboxALF Aft Looking ForwardALTN AlternateAOG Aircraft On GroundA/P AirplaneAPU Auxiliary Power UnitARINC Aeronautical Radio IncorporatedASM Autothrottle Servo-motorATA Air Transport AssociationA/T Autothrottle

BBITE Built In Test EquipmentBSI Borescope InspectionBSV Burner Staging Valve (SAC)BSV Burner Selection Valve (DAC)

CC Celsius/Centigrade (° degrees)CCDL Cross Channel Data LinkCCW Counter Clockwise

CDP Compressor Discharge Pressure (Ps3) CDS Common Display SystemCDU Control Display UnitCFMI Commercial Fan Motor InternationalCIP Compressor Inlet PressureCIT Compressor Inlet Temperaturecm.g Centimeter GramsCONT ContinuousCSD Constant Speed DriveCSI Cycles Since InstallationCTEC Customer Technical Education CenterCW Clockwise

DDAC Double Annular CombustorDEU Display Electronics UnitDMD Demand

EEAU Engine Accessory UnitEBU Engine Buildup Unit ECU Electronic Control Unit (or EEC)EE Electronic EquipmentEEC Electronic Engine Control (or ECU)EGT Exhaust Gas Temperature (T49.5) EHSV Electro-Hydraulic Servo Valve

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EESN Engine Serial Number

FF Fahrenheit (° Degrees)F/I Flight IdleFAA Federal Aviation AdministrationFADEC Full Authority Digital Electronic ControlFF Fuel FlowFIM Fault Isolation ManualFIT Fan Inlet TemperatureFLA Forward Looking Aft FMC Flight Management ComputerFMV Fuel Metering ValveFQIS Fuel Quantity Indicating System

Gg.in gram inchesG/I Ground IdleGEAE General Electric Aircraft EnginesGPH Gallons Per HourGPM Gallons Per MinuteGRD GroundGSE Ground Support Equipment

HHMU Hydromechanical Unit

HP High PressureHPC High Pressure Compressor HPCR High Pressure Compressor RotorHPT High Pressure Turbine HPTACC High Pressure Turbine Active Clearance

ControlHPTACCV High Pressure Turbine Active Clearance

Control ValveHPSOV High Pressure Shutoff ValveHz Hertz

IID Inside DiameterIDG Integrated Drive GeneratorIFSD In-flight Shutdown IGN IgnitionIGV Inlet Guide Vane in. inchesIPB Illustrated Parts BreakdownIPC Illustrated Parts Catalogips Inches Per Second

J

K°K Kelvin (Degrees)KIAS Indicated Air Speed in KnotsKV KilovoltsKPH Kilos Per Hour

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LL Leftlbs. Pounds, WeightL/H Left HandLP Low PressureLPC Low Pressure CompressorLPT Low Pressure Turbine LPTACC Low Pressure Turbine Active Clearance

Control LPTN Low Pressure Turbine NozzleLPTR Low Pressure Turbine RotorLRU Line Replaceable UnitLVDT Linear Variable Differential Transformer

Mma Milliamperes (Current)MCD Magnetic Chip DetectorMCL Maximum ClimbMCR Maximum CruiseMCT Maximum Continuousmm MillimetersMo Mach NumberMPA Maximum Power AssurancemV MillivoltsmVDC Millivolts Direct Current

NN1 Actual Fan SpeedN2 Actual Core Speed

OOAT Outside Air TemperatureOD Outside DiameterOSG Overspeed GovernorOVBD Overboard

PPb Bypass Pressure (5-265 psi)PBPB Regulated Body Pressure-Bypass

Pressure DifferentialPc Regulated Servo Pressure (290-310 psi)Pcb Regulated Body Pressure

(5-15 psi above Pb)Pcr Regulated Reference Pressure

(140-160 psi)Ps HMU Fuel Inlet PressurePsf Filtered Servo Supply Pressure

(0-15 psi below P1)Pso Metering Valve Shutoff PressurePt Pressure TapPx Modulated Servo PressureP1 Metering Valve Inlet Pressure

(1150-1204 psi)P2 Metering Valve Outlet Pressure

(50-60 psi below P1)P22 HMU Discharge Pressure (0-1000 psi)P2P Metered Flow Reference Pressure






PPo Pressure AmbientPPH Pounds Per HourPRSOV Pressure Regulating Shutoff ValvePs Pump Supply PressurePs13 Fan Outlet Static Air PressurePs3 Compressor Discharge Pressurepsi Pounds Per Square Inchpsia Pounds Per Square Inch Absolutepsid Pounds Per Square Inch DifferentialPT Pressure TotalPT25 High Pressure Compressor Total Inlet Air

Pressure

QQAD Quick Attach DetachQEC Quick Engine ChangeQty. Quantity

RR/H Right HandRPM Revolutions Per MinuteRTO Refuse TakeoffRVDT Rotary Variable Differential Transducer

SSAC Single Annular combustorsfc Specific Fuel Consumption

SLS Sea Level StandardSLSD Sea Level Standard DaySN Serial NumberSNECMA Societe d’Etude et de Construction de

Moteurs d’AviationSOV Shutoff Valve Control PressureSOVX Shutoff Valve Modulated PressureSTP Standard Temperature and PressureSW Switch

TTAI Thermal Anti IceTBV Transient Bleed ValveT/E Trailing EdgeT/O TakeoffT/R Thrust ReverserT12 Fan Inlet Total Air TemperatureT25 HPC Air Inlet TemperatureT49.5 Exhaust Gas TemperatureTAI Thermal Anti-IceTAT Total Air TemperatureTBC Thermal Barrier CoatingTBO Time Between OverhaulTCCV Turbine Clearance Control ValveTGB Transfer GearboxTLA Thrust Lever AngleTM Torque MotorTR Thrust ReverserTR Transformer Rectifier TRA Thrust Resolver AngleTRF Turbine Rear FrameTSI Time Since Installation






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HYDROMECHANICAL UNIT (HMU)

OBJECTIVES:Given an objective exercise the student will identify:...the HMU external ports. (1.B.a)...the HMU external electrical connections. (1.B.a)...the six EHSV's names. (1.B.a)...the HMU servo pressure regulators. (1.B.a)...the fuel metering valve components. (1.B.a)

Given an objective exercise the student will select the purpose:...of the HMU used on the CFM56-7 engine. (3.B.b)...of the shutoff shuttle valve. (3.B.b)...of the head sensor. (3.B.b)...of the HMU servo pressure regulators. (3.B.b)...of the overspeed governor. (3.B.b)...of the burner staging valve. (3.B.b)...of the airframe shutoff solenoid valve. (3.B.b)...of the fuel metering valve. (3.B.b)

Given an objective exercise the student will describe the operation:...of the HMU systems used on the CFM56-7 engine . (4.C.c)

Given an objective exercise the student will describe the function:...of the pressurizing and shutoff valve. (4.C.c)...of the selected EHSV's. (4.C.c)...of the bypass valve. (4.C.c)...of the overspeed governor. (4.C.c)

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HYDROMECHANICAL UNIT (HMU) – External View

Purpose (3.B.b)The purpose of the HMU is to control the fuel metering valve which supplies metered fuel to the combustion chamber and the servo systems.

The hydromechanical unit (HMU) receives fuel metering electrical signals from the EEC to control the various engine systems. The EEC control command signals are sent to the HMU and the HMU controls the hydraulic signals for engine servo system operation.

An internal fuel metering valve (FMV) in the HMU controls fuel flow to the combustion chamber.

The high pressure shutoff valve (HPSOV) when closed stops fuel in the HMU for the FMV and servo systems operation.

LocationThe hydromechanical unit (HMU) is at the 8:00 position, aft of the fuel pump. The fuel pump attaches to the aft side of the AGB. The HMU attaches to the aft side of the fuel pump assembly. To access the HMU open the left fan cowl.

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HMU EXTERNAL VIEW

OVERBOARD DRAINPCR

BSV

VBV OPEN

VBV CLOSED

AIRFRAME SHUTOFFVALVE SOLENOID

(HPSOV)

VSV ROD

VSV HEAD

HPTACCLPTACC

TBV

CH B

CH A

AIRFRAME SHUTOFF INDICATORSWITCH CONNECTOR

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HYDROMECHANICAL UNIT

Identification (1.B.a.)These are some of the hydromechanical unit (HMU) fuel and electrical connections and ports:

- EEC channel A electrical- EEC channel B electrical- Airframe shutoff indication shutoff switch connection- EHSV's cover- BSV port- VBV open port- VBV closed port- PCR port- Drain line.

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OVERBOARDDRAIN PORT

CHANNEL BAIRFRAME SHUTOFF INDICATOR SWITCH CHANNEL A

PCR PORT

BSV PORT

VBV OPENPORT

VBV CLOSEDPORT

EHSV’S COVER

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HMU External View

Identification (1.B.a.)These are the hydromechanical unit (HMU) fuel and electrical connections and ports:

- LPTACC port- HPTACC port- Servo supply port- Heated servo- P1 port- P2 port- Discharge port- PC regulator- Bypass Valve- Bypass discharge- Head sensor

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P2 PORT DISCHARGE PORT

P1 PORT HEAD SENSOR BYPASS DISCHARGE

LPT PORT

HPT PORT

SERVOSUPPLYPORT

BYPASS VALVE

HEATEDSERVO

PC REGULATOR

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HMU External View

Identification (1.B.a.)These are the hydromechanical unit (HMU) fuel and electrical connections and ports:

- EEC channel A electrical connection- EEC channel B electrical connection- Airframe shutoff indication switch connection- EHSV's cover- several components under HMU cover- TBV open port- PCR port- Overboard drain port.

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AFSO REED SWITCH (HPSOV) METERING VALVE UNDER COVER

TBV PORT

AIRFRAME INDICATORSHUTOFF SWITCHCONNECTOR

CHANNEL ACHANNEL B

OVERBOARDDRAIN PORT

INTERGRATOR VALVEUNDER COVER

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HMU External View

0perational OverviewThe CFM56-7B engine, is controlled by a Full Authority Digital Electronic Control system called FADEC, which includes the airplane interfaces.

The engine control system side of the FADEC system, is composed of two major engine components:

- An Electronic Engine Control Unit (EEC) or ECU- A Hydromechanical fuel control Unit (HMU)

The EEC receives electrical feedback signals from various remotely mounted engine sensors and after processing the signals, the EEC transmits electronic command signals to the HMU.

The HMU then converts the computed electronic command signals into hydraulic command signals for controlling various engine servo systems.

The EEC and the HMU control the high pressure fuel to the actuators for the positioning of the Variable Stator Vanes (VSV) and the Variable Bleed Valves (VBV).The Burner Staging Valve (BSV) is also controlled by the HMU, as well as regulating fuel pressure to the valves for the clearance control systems and the transient bleed air system:

- TBV- HPTACC- LPTACC

Other features include the control of the fuel flow to the engine for combustion, a system for engine shut-down and pump unloading.

In addition, the HMU provides a compensated isochronous mechanical overspeed protection governor that operates independently of the EEC. Should the EEC fail to control the engine at 106% N2 overspeed condition, the HMU overspeed governor would.

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PCR PORTPCR PORT BSV PORT

OVERSPEEDGOVERNOR

PC REGULATOR

LPT PORT HPT PORT

VSV HEADPORT

VSV RODPORT

SHUTTLESHUTOFF

AIRFRAME SHUTOFFVALVE SOLENOID(HPSOV)AND ELECTRICALCONNECTOR

PSF PORT (DAC)

PCB PORT (DAC)

VBVCLOSEDPORT

VBV OPENPORT

TBV PORT

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PRESSURIZING AND SHUTOFF VALVE

Functional Description (4.C.c)The pressurizing and shutoff valve performs two functions;1. Assure that servo operating pressures are in regulation during engine starting.2. During low flow conditions act as the fuel delivery shutoff valve during engine shutdown.

The HPSOV solenoid receives it's signal from the flight compartment. It is used to start or stop metered fuel to the fuel nozzles. The HPSOV solenoid is an integrated assembly that provides aircraft and control of fuel flow to activate the pressurizing and shutoff valve hydraulically.

The pressurizing and shutoff valve has two functions;1. To assure servo pressures are correct before

engine starts and low flow conditions.2. To assure positive fuel shutoff during engine

shutdown.

During engine operation, the pressurizing valve establishes a minimum Psf pressure to ensure proper operation of Pc and Pcr regulators, and adequate piston force margins. During engine shut-down, the pressurizing valve closes to stop fuel flow to the engine fuel nozzles. The pressurizing valve is composed of:

- A piston- A preloaded spring- Two position switches

Under normal operation, a Pcb pressure combined with a preloaded spring force is applied on the back while the FMV downstream pressure is applied to the face of the piston.

A minimum FMV downstream pressure is required to displace the valve piston far enough to open a port in the sleeve.

The preloaded spring force is adjusted high enough to guarantee enough Psf to operate Pc, Pcr and Delta P regulator system, as well as providing adequate force margins for all piston and actuators.

Under engine shut-down conditions, the shut-off system exchanges the Pcb pressure for a Psf pressure resulting in a closed valve position.

The fuel supply to the nozzles is stopped, then the engine shuts-off. The pressurizing valve is provided with a shut-down position indicator which signals to the EEC that the pressurization valve is in the shut-down position which is displayed in the flight comparton the engine valve closed light. The magnet in the pressurizing valve closes the reed switch in the AFSO switch.

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PRESSURIZING AND SHUTOFF VALVE

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ELECTRO-HYDRAULIC SERVO VALVES

Identification (1.B.a)There are six EHSV'S:

- The fuel metering valve (FMV) EHSV- The transient bleed valve (TBV)EHSV- The high pressure turbine clearance control

(HPTACC)EHSV- The low pressure turbine clearance control

(LPTACC)EHSV- The variable bleed valves (VBV) EHSV- The variable stator vanes (VSV) EHSV

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ELECTRO-HYDRAULIC SERVO VALVES

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ELECTRO-HYDRAULIC SERVO VALVE LOCATION

Identification (1.B.a)There are six EHSV'S:

- The fuel metering valve (FMV) EHSV- The transient bleed valve (TBV)EHSV- The high pressure turbine active clearance control

(HPTACC)EHSV- The low pressure turbine active clearance control

(LPTACC)EHSV- The variable bleed valves (VBV) EHSV- The variable stator vanes (VSV) EHSV

The external connections are:- Channel A- Channel A- Airframe shutoff indication connector- HMU Ports:

TBVVBV OpenVBV ClosedBSVPCROverboard Drain

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ELECTRO-HYDRAULIC SERVO VALVE

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ELECTRO-HYDRAULIC SERVO VALVE

Functional DescriptionThe EEC command signals are sent to the HMU EHSV's that change the electrical inputs to hydraulic outputs to the servo systems. The servo systems then operate the valve or actuator to the correct position schedule. The positioning is verified by the EEC, through feedback signals from the component LVDT, RVDT, or resolvers that give actual positioning.

The operation of the EHSV is done by the use of a torque motor that converts the electrical signal inputs from the EEC to modulate a hydraulic servo output through a spool valve.

One four way EHSV controls the fuel metering valve.The three way EHSV's control the other 5 servo systems.

Each EHSV is a two stage valve operated by a torque motor armature that controls the fluidic amplifier. The first stage of the EHSV is a fluidic amplifier and the second stage is a spool valve. The first stage fluidic amplifier operates the second stage spool valve in response to input from the torque motor which receives command signals from the EEC.

Fluidic AmplifierThe fluidic amplifier directs high pressure fuel to ports that deliver the fuel to either side of the spool valve. In the null position the spool valve is not sending out command signals.

A feedback spring holds the spool valve in the neutral position.

The spool valve directs the servo pressures to control the actuator positioning of the VBV's and the VSV's. The other valves are either closed or opened to the correct schedules, the HPTACC and LPTACC valves, the TBV, and the FMV.

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THREE AND FOUR WAY ELECTRO-HYDRAULIC SERVO VALVE

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FLUIDIC AMPLIFIER

Purpose (3.B.b)The nozzle can go left or right from the null position. The fuel pressure will flow equally at this position.

When the EEC command signal commands the torque motor to reposition the fluidic amplifier. This is done by the deflection of the armature in the torque motor that repositions the fluidic amplifier . This will cause the nozzle to go either side of the spool valve and the fuel flow will redirect the spool valve which causes a servo output change.

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FLUIDIC AMPLIFIER

HIGHPRESSUREFUEL

HIGHPRESSUREFUEL

NOZZLE NOZZLE

NULLPOSITION

A BB A

MOVEMENT FROM THE NULL POSTION

AT THE NULL POSITIONFUEL FLOWS ARE EQUAL

NOZZLE MOVED FROM THENULL POSITION CHANGESTHE FUEL FLOW, HERE BFUEL FLOW IS GREATERTHAN ANOTE: THE EEC SIGNAL CHANGES TORQUE MOTOR

CURRENT AND THE TORQUE MOTOR CAUSES THENOZZLE DEFLECTION.

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SHUTOFF SHUTTLE VALVE

Purpose (3.B.b)The shutoff shuttle valve is a two position valve that directs P2 or SOVX flow to the head sensor bellows.

PCB is supplied to the rod end of the valve and through a restrictor and an adjustable bleed in the valve bore to the head end of the valve used for the HMU shutoff circuit.

During normal engine operation both ends of the valve have PCB. Spring force against the piston end of the valve positions the valve to direct P2 to the head sensor bellows. The P2 flow path is from downstream of the metering valve orifice, to the groove in the shutoff shuttle valve, to the head sensor bellows.

During engine shutdown the PCB at the spring end of the valve is replaced by P1/PSF. The bleed in the shutoff valve bore allows the buildup of the P1/PSF at the head end of the valve. The increase pressure moves the shuttle valve against the PCB and spring force to position the valve at the shutoff position.

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SHUTOFF SHUTTER VALVE

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HEAD SENSOR

Purpose (4.B.b)The head sensor and bypass valve work together to maintain the metering valve P1-P2 pressure differential. Both systems operate on the fuel stream between the fuel inlet and the metering valve.

Functional Description (4.C.c)The head sensor and bypass valve operationally are described together to maintain the fuel metering valve P1-P2 pressure differential. Both valve actions return fuel that is excess back to Pb or the engine fuel LP stage pump outlet.

The head sensor positions the bypass valve to establish control of the amount of excess bypass fuel return or Pb. The amount of Pb is determined by P1- P2 metering head and spring force acting on the head sensor servo valve to control the orifice area. When P1 is equal to P2P and the spring force on the servo valve then a null condition exists.

If P2P is too high the servo orifice closes to increase servo system operational pressure. If P1 is too high the servo orifice opens to reduce servo system operational pressure.

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HEAD SENSOR

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BYPASS VALVE

Functional Description (4.C.c)The bypass circuit is composed of a bypass valve that works with the head sensor and overspeed governor to control fuel unmetered that exceeds the metered fuel requirements of the FMV. This excess fuel is routed back to the outlet side of the LP pump.

P1 or Ps goes to one side of the bypass valve while P2P and spring force act opposite to P1 to position the bypass valve. The P1-P2P differential is maintained at 50-65 psid. A proportional bypass valve moves the integrator bypass valve bore until forces on both sides of the proportional valve are balanced. The P1 to Pb bypass flow orifice is now established. The integrator bypass valve orifice is variable yet does not fully close or open during operation of the HMU. This allows for the quick response to pressure changes in P1 and P2 head fluctuations.

Engine shutdownWhen the fuel metering valve closes there is decrease in P2. P1 then goes to the airframe shutoff solenoid valve and the pressurizing and shutoff valve. P1 positions the shutoff shuttle valve to the shutoff position which closes the P2 supply to the head sensor. P2P decreases on the head sensor side to the shutoff shuttle valve intermediate pressure SOVX. Servo pressure on the spring side of the bypass valve is reduced. P1 moves the bypass valve to the open position and P1 is vented to Pb.

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BYPASS VALVE

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SERVO PRESSURE REGULATORS

Purpose (3.B.b.)The pressure regulation system purpose is to provide the HMU with working fuel pressures. The servo pressure regulators establish the correct fuel pressures needed for PC, PB, PCR and PCB. Primary working fuel pressures are used by the HMU for internal systems and to actuate servo-mechanisms. To perform different required functions, the HMU divides and regulates the fuel supplied by the engine fuel pump into different internal system components. (Refer to the HMU CMM for more details.)

Identification (1.B.b)Pc Servo Pressure Regulator = (PCB + 300 psig)PC is referenced to regulated body pressure PCB and is maintained at a constant level of 300 psid above PCB. The regulator controls Psf or dumps Pc to Pb in order to maintain a constant pressure differential throughout the range of flow demanded downstream and to compensate for varying Pb pressures. Pc fuel pressure is distributed to these components:

- PCR servo pressure regulator- Fuel metering valve EHSV - LPTACC EHSV- HPTACC EHSV - BSV solenoid- Speed servo valve

Pcr Servo Pressure Regulator = (PCB + 150 psig)Pcr pressure is regulated by the Pcr pressure regulator at a constant value above Pcb.

The Pcr regulator functions identically to the Pc regulator,however the preload spring is calibrated to 150 psid.

Pcr fuel pressure is distributed to these components:- Head end of the integrator piston- LPTACC valve- HPTACC valve- TBV- BSV solenoid

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PC - PCR SERVO PRESSURE REGULATORS

PC SERVO PRESSURE REGULATOR PCR SERVO PRESSURE REGULATOR

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OVERSPEED GOVERNOR (OSG)

Purpose (3.B.b.)The purpose of the overspeed governor in the HMU, is a mechanical backup for the EEC in the event of an overspeed condition at 106% N2.

Functional Description (4.C.c)During start the OSG is tested to ensure it's operation is good. At 38-48% N2 and a signal is sent to the EEC that the OSG test has been done and the OSG is in a standby condition until needed. Spinning flyweights position a spool valve, which is established by the speed of the N2 system. The flyweight force is balanced by reference springs. At 106% N2 the flyweight force will overcome the spring force and the spool valve moves. P2P then goes to PCB, reducing the P2P pressure on the head sensor and bypass valve. This opens the bypass valve which reduces the P1-P2 drop across the FMV and the metered fuel to the fuel nozzles is reduced. The overspeed condition is maintained at 106% N2.

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OVERSPEED GOVERNOR

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OVERSPEED GOVERNOR INTEGRATOR VAVLE

Purpose (3.B.b)The purpose of the overspeed governor integrator valve in the HMU is to work with the overspeed governor, head sensor and bypass valve to control fuel flow when N2 is at 106%. Normally the EEC controls N2 speed, but the OSG is a backup system for the EEC.

During start the OSG is tested to ensure its operation is normal. Between 38-485 N2% the OSG position switch opens and the EEC now knows the OSG system operates.

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OVERSPEED GOVERNOR INTEGRATOR VALVE

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BURNER STAGING VALVE

Purpose (3.B.b)The purpose of the burner staging valve, that is interfaced with the EEC, is to provide the schedule logic of the EEC and operate the BSV for fuel nozzle scheduling. The solenoid is electrically operated by the EEC. Normal operation called unstaged, allows 20 fuel nozzles and another mode staged allows 10 nozzle operation.

The BSV is a two position solenoid operated valve inside the HMU. During engine operation the BSV receives a command signal from the EEC to allow the staging of the fuel nozzles. PC and PCR are being supplied to the BSV, which gives the hydraulic of to the burner staging valve on the engine for the fuel nozzle staging control.

Note: Later models of CFM56-7B engines do not have the BSV installed for the SAC version, the DAC remains the same.

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BURNER STAGING VALVE

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Airframe Shutoff Solenoid Valve

Purpose (3.B.b)The airframe shutoff solenoid is activated by 28 VDC from a switch from the flight compartment. This interface for the HMU gives you a manual shutdown which the purpose of the valve. If power is interrupted to the system, the solenoid willremained latched, this prevents repositioning of the valve.This system is provided to ensure:

-Engine shut-down-Fuel metered fuel flow stops.

Two operations to be considered:-EEC automatic engine shut-down during enhancedstarting sequence by the FMV.-Engine manual shut-down from the start levers or fire switches.

During a shut-down command, a shut-off hydraulic signal is generated.

The SOV signal activates a shut-off shuttle valve which:-Closes the pressurizing valve to stop fuel nozzles supply.

-Opens the bypass valve to return to the fuel pump.

The pilot shut-down command is done by the start levers or fire switches, which energizes the airframe shut-off solenoid located on the HMU to the fuel cutoff position.

The EEC automatic shut-down command is provided from the EEC fuel metering valve control logic, which can stop fuel flow in the enhanced start mode by positioning the FMV to the shutoff position.

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AIRFRAME SHUTOFF SOLENOID VALVE

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FUEL METERING VALVE

Purpose (3.C.c)The purpose of the fuel metering valve is to control metered fuel. The FMV is controlled by the EEC through a FMV EHSV. The correct metered fuel is then sent to the fuel nozzles.

Resolvers receive mechanical feedback and transmits the position feedback as electrical signals to the EEC that determines actual positioning of the FMV. Through the FMV control logic, the EEC orders the FMV to move so as to modify the metered fuel flow. There are two resolvers, one for channel A and the other for channel B of the EEC. The FMV resolvers provide the EEC an electrical feedback signal proportional to the FMV position to achieve closed loop control for channels A and B. EEC logic then controls the metered fuel flow for engine operation.

The bypass valve ensures that FMV fuel flow is proportional to the FMV area by maintaining a constant pressure drop of 55-60 psi above P2 in the FMV. If both FMV resolvers fail in flight the EEC will use the fuel flow meter to maintain engine operation. This will effect the acceleration schedule, but the engine will continue to operate.

Identification (1.B.b)The HMU fuel metering system consists of:- Fuel Metering Valve (FMV)- Fuel Metering Valve Resolvers- EEC Control System Logic- Bypass Regulating System- Electro-Hydraulic Servo Valve (EHSV).

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FUEL METERING VALVE

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HYDROMECHANICAL UNIT SYSTEMS

Operational Description (4.C.c)The engine control system made up of two major engine components:- Electronic Control Unit (ECU) or

Electronic Engine Control (EEC)- A Hydromechanical fuel control Unit (HMU)

The EEC receives electrical feedback signals from various remotely mounted engine sensors and after processing the signals, the EEC transmits electronic signals to the HMU. The HMU then converts the computed electronic signals into hydraulic signals for controlling various engine systems. When coupled to the EEC, the HMU controls the high pressure fuel to the actuators for the positioning of the Variable Stator Vanes (VSV) and the Variable Bleed Valves (VBV). The Burner Staging Valve (BSV) is also scheduled by the EEC/HMU. Other features include the control of the fuel flow to the engine for combustion, a system for engine shut-down and pump unloading. In addition, the HMU provides a compensated isochronous overspeed protection feature that operates independently of the EEC command.

The HMU is interfaced with the EEC that provides the logic for the operation of the EHSV'S, which in turn controls engine system operation.

The HMU is the muscle for the electronic brain called the EEC. It provides the exchange of electrical inputs to hydraulic or mechanical outputs. The EEC then monitors feedback from various systems to ensure proper scheduling or positioning of that system.

A mechanical OSG provides backup protection for the EEC in the event of a malfunction of the EEC in an overspeed condition of the engine.

The HMU regulates various pressure operations that are used in the servo circuits.

The HMU is also interfaced with the airplane to allow the pilot manual engine shutdown capability.

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HMU SYSTEMS

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HMU Operational Description (cont.)The hydromechanical unit (HMU) controls the six servo systems. The EEC and the HMU controls these six electro-hydraulic servo valves (EHSV):

- Fuel metering valve (FMV) EHSV-Transient bleed valve (TBV) EHSV- High pressure turbine active clearance control valve

(HPTACC) EHSV- Low pressure turbine active clearance control valve

(LPTACC) EHSV- Variable bleed valves (VBV) EHSV- Variable stator vanes (VSV) EHSV.

The hydromechanical unit (HMU) uses two solenoids to control shutoff high pressure fuel flow and to operate the burner staging valve (BSV). These are the two solenoids:

- Engine high pressure fuel shutoff valve (HPSOV) solenoid

- Burner staging valve (BSV) solenoid.

The EEC commands the the HPSOV to open when the EEC receives the start lever open signal. The HPSOV close position is by EEC command close signal at start or a direct command close signal from the start levers. When you raise the fire switch the HPSOV closes to stop fuel flow. On the P5-2 panel the ENGINE VALVE CLOSED light will come on when the HPSOV closes.

Metered Fuel ControlFuel from the fuel pump goes to the HMU. A fuel metering valve (FMV) controls how much fuel goes to the fuel nozzles for combustion. The EEC controls the FMV EHSV on the HMU that controls the FMV position. The FMV resolver sends actual position of the FMV to the EEC.

Overspeed ProtectionThe EEC controls primary N2 overspeed protection for the engine. The HMU uses a secondary mechanical overspeed governor for N2 overspeed protection (106% N2). The accessory gearbox turns the HMU drive shaft through the fuel pump assembly.

High Pressure Fuel Shutoff Valve (HPSOV)The engine high pressure fuel shutoff valve control permits or stops the fuel flow to the engine fuel nozzles.

HMU Servo System ControlThe HMU uses the EEC electrical command signals to change them to hydraulic servo fuel pressure signals.The EEC and the HMU control these six servo system components:- Fuel metering valve - Transient bleed valve- High pressure turbine active clearance control valve- Low pressure turbine active clearance control valve - Variable bleed valves actuators - Variable stator vanes actuators.

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CFM56-7 HMU SCHEMATIC

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HMU Operational Description (cont.)

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HMU Operational Description (cont.)

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