Common Rail Systems Chapter 30

1. Common Rail SystemsChapter 30 DSL - 131

2. OBJECTIVES • Identify common rail (CR) diesel fuel systems. • Identify some of the diesel engines currently using common rail diesel fuel injection. • Outline the fuel subsystems in a typical CR system. • Trace fuel flow routing from tank to injector on common rail, diesel-fueled engines. • Describe the electronic management circuit components used in common rail fuel systems. • Describe the operation of the inline and radial piston pumps used to achieve sufficient flow to produce rail and injection pressures in a typical CR system. • Understand how rail pressures are managed in electronically managed, common rail diesel fuel systems. • Outline the operation of an electrohydraulic injector. • Identify some of the characteristics of different OEM common rail diesel fuel-injection systems.

3. INTRODUCTION • Electronically controlled, common rail (CR) diesel fuel injection systems were introduced on small-bore and automobile diesel engines in the late 1990s. • These systems were manufactured by Robert Bosch and Delphi Lucas, and both had similar operating principles. • Early systems had about 20,000 psi rail pressure. • Newer versions may exceed 35,000 psi. • According to the EPA, by 2010 nearly all major diesel OEMs is using a CR system on at least one of their engine families to meet emission/performance standards.

4. What is CR? • CR only refers to systems where fuel injection pressure is maintained at the fuel rail that directly feeds the injectors. • Beginning in 2008, second generation CR systems were developed where rail pressures are amplified at the injector prior to injection were introduced. • CRs and/or amplified CRs do not use oil pressure or mechanical action to amplify the injection pressure (see chapter 31).

5. Function of the Rail • During this presentation the term rail describes the supply manifold or gallery that directly feeds all of the fuel injectors. • Similar to gasoline fuel injection. • Major differences: • CR operates at higher pressures (in some cases above 35,000 psi) • CR precisely manages rail pressure within a wide range of values. • Similarities • Managing and switching injectors. • Injector units are similar, especially when considering DI (gasoline Direct Injection).

6. CAUTION • Do not confuse post-2007 and post-2010 engines with their earlier versions, even if they are nominally the same series. • In most cases, the fuel system, engine displacement, and emissions control apparatus are completely different.

7. ADVANTAGES OF CRDIESEL FUEL SYSTEMS • CR systems are simpler mechanically than earlier systems leading to higher reliability. • Electronics have much more control over fueling for better combustion control. • Specific improvements: • Lower emissions • Improved fuel economy • Lower engine noise levels • Optimization of cylinder pressures • Made possible by: • Improved metallurgy • Development of electrohydraulic injectors w/faster opening/closing events at nozzle.

8. CR SUBSYSTEMS AND COMPONENTS • Fuel subsystem • Stores and supplies fuel to the high-pressure rail pump. • High-pressure pump • Engine driven pump capable of producing pressures of up to 35,000 psi or more. • May be of either radial piston or multiple cylinder inline design. • ECM-controlled rail pressure control valve • A linear proportioning solenoid with built in spool valve • Is an ECM output.

9. CR SUBSYSTEMS ANDCOMPONENTS (Cont.) • A V-Ref supplied rail pressure sensor • Signals “actual rail pressure to the ECM continuously. • Enables “closed loop” capabilities. • CR • Stores fuel at injection pressure. • AKA high pressure accumulator. • EHIs (Electronic Hydraulic Injector) • Act as ECM switched hydraulic valves. • Injects fuel at close to rail pressure values

10. CR Special Features • Reasons for CR acceptance: • Ability to achieve high injection pressures independent of engine speed. • Ability to control droplet size for best performance under all conditions. • Ability to switch EHIs at high speed. • Currently up to 7 “events” during a single power stroke. • Overall better management of fuel for: • Improvedfuel economy. • Reduced emissions • Improved response to power change requests. • Improved cold starting. • Finely atomized fuel at cranking and cold idle conditions.

11. CR Management Electronics • CR is a full authority system. • Fuel quantity determined by ECM • ECM monitors: • Ambient conditions • Chassis conditions • Engine conditions • ECM can determine electronic and hydromechanical faults. • ECM may initiate: • Torque limitation • Power de-rate • Limp home mode • ECM can interface with other chassis and powertrain components.

12. CR MANAGEMENT ELECTRONICS • Input Circuit • Sensor circuit inputs to the ECM to include: • Electronic signal transducers • Electronic signal amplifiers • Fluid pressure transducers. • Analog Inputs • Include • Mass airflow • Engine fluid and intake air temps • Battery voltage • Converted to digital values by the A/D converter in the ECM • Some analog signals are converted to digital by the sensor.

13. CR MANAGEMENT ELECTRONICS • Digital Inputs • Includes • On-off switching signals • Digital sensor signals (RPM and component position) • Bypass the A/D unit • Signal Conditioning • Reduce voltage to a specific range • Filter out spikes and lows • Amplify to system signal levels. • Reduces noise.

14. CR MANAGEMENT ELECTRONICS • Processing Cycle • Compares input signals to operational maps (algorithms) • Limited editing may be available to OEM or technician. • May include: • Failure strategies • Calibration data • Power trim/derate programming • Post 2008 • Log faults to EEPROM • Communicate with J1939 data bus (allows communication with chassis electronic systems.

15. CR MANAGEMENT ELECTRONICS • Fueling Algorithm • Primary function is closed loop cycle between desired fuel pressure and actual fuel pressure. • Desired fuel pressure – what the ECM computes that it needs. • Actual fuel pressure – what the transducer actually measures at the fuel rail. • Fueling concerns. • Minimizing emissions • After 2010 may include: • EGR – exhaust gas recirculation • Catalytic converters • DPF - diesel particulate filters • SCR – selective catalytic reduction systems

16. CR MANAGEMENT ELECTRONICS • Output Circuit • Rail Pressure Management Control (RPMC) • PWN (pulse width modulated) output to control valve • Fuel directed to fuel rail or return as necessary to control pressure. • NOTE: This valve is spring loaded and will default to the bypass condition in the event of electrical failure, shutting down the engine. • Injector Drivers • PWM signal to EHIs • Usually spiked to 100vdc for solenoid injectors, sometimes less to piezoelectric units. • Current draw usually lower to piezoelectric units.

17. CR FUEL ROUTING CIRCUIT • The CR fuel routing system is modular so, for purposes of study, we can divide it up as follows: • Fuel subsystem • Items 1-5 • Transfer or Presupply pump may be • Electric and located in fuel tank • Mechanical on the engine • Supplies fuel to high pressure pump. • Fuel filter • OEM responsibility • Nominally 8 microns. • Should have water separator

18. CR FUEL ROUTING CIRCUIT • High-pressure pump • Item 6 • May be 3 cylinder radial pump (Bosch & Denso) • May be inline piston as used by Caterpillar. • All pumps are capable of maintaining injection pressure at rated engine speed and load. • Unneeded fuel is returned to the tank via rail pressure control valve.

19. Radial Piston, High-Pressure Pump

20. Caterpillar CR System High-pressurePump

21. CR Fuel Routing Circuit. • Rail pressure control valve. • Solenoid is electrical • Slow response to maintain/increase pressure • Spring return is mechanical • Quickly compensate for pressure fluctuations/reduce pressure.

22. Caterpillar CR High-Pressure Pump and the Solenoids that Act as Rail Pressure Control Valves • Similar in operation to the Bosch unit. • When energized, closes the valve pressurizing the rail. • When de-energized spring pressure opens valve sending fuel to the low pressure return circuit.

23. CR FUEL ROUTING CIRCUIT • Pressure accumulator or rail • Item 8 • Acts as an accumulator and dampens pulses.

24. Bosch Common Rail

25. CR FUEL ROUTING CIRCUIT • Electrohydraulic injectors • Item 9

26. CAUTION • Never attempt to prime a CR fuel system equipped with an inline gear pump using shop air pressures applied anywhere in the fuel subsystem: Pressurized air can blow out the transfer pump seals. • If the transfer pump seals fail, the pump must be replaced.

27. Rail Pressure Sensor • May be • Piezoelectric (most common) • Capacitance • Wheatstone bridge. • Uses a 5 vdc reference. • Analog output

28. Flow Limiter • In the event an injector is stuck open, the valve will close stopping fuel flow to the injector.

29. Location of Quill Tube Recess on a Cylindrical Caterpillar EHI

30. Rail, High-Pressure Pipe, and Quill Tube Disassembled and Assembled on the Engine

31. WARNING • Never crack the high-pressure pipe nuts attempting to bleed them. It could prove to be dangerous and most OEMs prefer CR high-pressure lines to be single-use devices. (They yield to deform on initial torque to form a better seal.) • CR fuel systems are designed to self-prime.

32. ELECTROHYDRAULIC INJECTORS • Two general types of Electrohydraulic injectors (EHIs) are used, differentiated by the type of actuator used: • First generation EHIs used a solenoid control valve • Some more recent types use piezoelectric actuators.

33. ELECTROHYDRAULIC INJECTORS (Cont.) • We use a Bosch EHI for purposes of the description here. • An EHI can be subdivided as follows: • Nozzle assembly • Hydraulic servo-system • Actuator valve

34. https://www.youtube.com/watch?v=zbOzX_OFDIg • https://www.youtube.com/watch?v=cIkMtnd3LGQ

35. CAUTION • Never attempt to locate an engine miss by cracking open the high-pressure lines that feed the EHIs. • Use OEM technical literature to troubleshoot engine as well as fuel system malfunctions.

36. Denso EHI Five-Phase Multipulse Injection Cycle Represented Graphically

37. https://www.youtube.com/watch?v=ftchx1TDNJo • http://www.dailymotion.com/video/xkxog1_diesel-piezo-injector-pulse-n-pressure_auto

38. PHASES OF INJECTION • On common rail systems, multiple injection events can occur during one power stroke. • Pilot injection • Small amount of fuel injected just prior to main injection. • Improves combustion efficiency • Reduces noise • More even torque production (smoother pressure curve) • Main injection • Multiple pulses into the established flame front. • Essentially nibbles at power stroke rather than gulp. • Dosing • AKA afterburn. • Small amount of fuel injected after combustion has ended. • Does not burn in the combustion chamber/cylinder. • Provides temporary rich mixture to rhodium catalyst to reduce NOx emissions. • Some fuel may be transmitted back to the intake via the EGR system to provide some “pilot” injection effect.

39. CR INJECTOR CALIBRATION PROGRAMMING • Most CR fuel systems require their ECMs to be programmed with a fuel flow code specific to each EHI. • The fuel flow code is the injection quantity calibration data. • Caterpillar uses the term E-trim, and Denso uses the term quick response (QR) code. • Matches fuel flow characteristics so that all function similarly.

40. CAUTION • Injection quantity calibration data or E-trim must be programmed to the ECM every time an EHI is changed out. • This may require entering a numeric code, located on the injector, into the injector calibration field using an electronic service tool (EST). • Alternatively, it may require connection to the OEM data hub to download a calibration file to the engine ECM. • Failure to reprogram E-trim can result in unbalanced engine fueling.

41. ADAPTIVE TRIM • Most CR management electronics complement injector quantity calibration with adaptive trim. • Evaluates EHI performance at hourly intervals and “corrects” fuel flow programming. • AKA “a-trim”

42. Location of the QR Code on a Denso EHIUsed on a Hino Engine • Codes are used to calibrate the ECM to evenly match cylinder performance.

43. Caterpillar High-Pressure Pump TimingPin Locked into Position • Some systems require the high pressure pump to be timed to the engine. • This is to make sure that the pressure pulses align with the operating pulses of the injector units and maintain smooth pressure cycles at the rail.

44. Diagnosing CR System Problems • Until fairly recently, troubleshooting EHIs was usually a matter of using OEM software to identify a malfunctioning component, then replacing the defective unit. • The number of CR fuel systems in service has resulted in an extensive repair infrastructure.

45. Diagnostic Routines • It should be emphasized that the three requirements of accurately diagnosing CR problems are: • Data bus connection hardware • OEM diagnostic software • Access to the OEM service information system (SIS) • As of 2013, the introduction of mandatory HD-OBD may provide some generic testing codes.

46. Bosch EHI Being Prepped for Testing

47. Easy to Access Location of the EHIs on a Post-2010 Cummins ISB Engine

48. WARNING • When working with CR fuel systems, never crack the high-pressure pipe nuts attempting to bleed or troubleshoot problems. • It could prove to be dangerous and result in costly system malfunctions. • Note that most (but not all) OEMs prefer CR high-pressure lines to be single-use devices. • (They yield to deform to shape on initial torque.) • CR fuel systems are designed to self-prime, so there is no reason to crack the pipe nuts after initial torque.

49. SUMMARY • Common rail (CR) diesel fuel systems are currently used on a wide range of engines that extend from small- to large-bore highway diesels. • CR diesel fuel systems have full authority engine management capability and are networked to J1939 data buses. • The fuel subsystems that supply CR fuel systems have few functional differences when compared with other current fuel supply circuits. • The electronic controls on a typical CR system consist of an input circuit, processing hardware, and actuator circuit. • The primary outputs that manage fueling on a CR system are the rail pressure control valve and the switching of the EHI actuators. • Bosch CR systems use either radial piston high-pressure pumps or inline piston pumps.

50. SUMMARY (Cont.) • The Caterpillar CR system on C7 and C9 engines uses an inline piston, high-pressure pump. • Rail pressures on CR diesel fuel systems are managed by the ECM using a rail pressure control valve. This applies flow restriction to fuel discharged by the high-pressure pump and options it either to the rail or to the return circuit. • The rail pressure control valve is a linear proportioning solenoid with an integral spool valve. It options fuel from the high-pressure pump outlet either to the rail or to the fuel return circuit. • Actual rail pressures are signaled to the ECM by the rail pressure sensor. • Rail pressure sensors use a piezo-resistive operating principle.