Mechanical-142-196 Student Text PDF

G c G G c G C c G G c c G c C c c Air Intake & Exhaust Systems c G C introduction G In this chapter we will.Jok at the two types of air intake systems, roots blowers, 6 and turbochargers, with the...

G c G G c G C c G G c c G c C c c Air Intake & Exhaust Systems c G C introduction G In this chapter we will.Jok at the two types of air intake systems, roots blowers, 6 and turbochargers, with their related exhaust components. c Turbochargers G G The turbocharger assembly, Fig. 7-1, is primarily used to increase engine horsepower and provide better fuel economy through the utilization of exhaust gases. G As shown in cross-section, the turbocharger has a single stage turbine with a connecting gear train. G c The connecting gear train is necessary for engine starting, light load operation, and rapid acceleration. Under these conditions, there is insufficient exhaust heat energy to c drive the turbine fast enough to supply the necessary air for combustion, and the engine is actually driving the turbocharger through the gear train assisted by exhaust gas energy. e. p>v c When the engine approaches full load, the heat energy in the exhaust, which reaches temperatures approaching 1000°F (538OC),is sufficient to drive the turbo- G charger without any help from the engine. At this point, an overrunning clutch in the drive train disengages and the turbocharger drive is mechanically disconnected from the G engine gear train. c G c ITS LocomotiveTraining Series -Student Text 7-1 c A  3 COMPONENT FAMILIARIZATION The next section is designed for familiarization with the major turbocharger components. These include the doweling assembly, the turbine wheel, the gear- drive assembly, etc. Minor pa& such as hardware, brackets, etc. will not be covered unless these items perform some special function. Figure 7-1 Turbocharger Turbocharger Nameplate I G --- ELECTRO-MOTIVE La Grange, Illinois, U S A. @ Figure 7-2 Turbocharger Nameplate -SERIAL NO. IDENTIFICATION CODE @ Part Number The part number specifies exactly what model the turbo is; i.e., 16 cylinder 3 marine turbo, etc. An EMD parts catalog such as #300 will provide a turbo applica-. tion list on Parts List #174. This chart will indicate specifically what turbo is re-. u quired on each engine. 3 14 4d AJ ICJ) 7-2 ElectrcMotive Model 567,645 & 710 Series Diesel Engines L) A L A C c c c c Serial Number G The serial number indicates the date, production sequence number, and assembly G location of the turbo. For example: G C e Year Month * Type * Plant * Sequence * (1988) c (Jan) (New) (LaGrange) (#5) c * Month: A = January, B = February, etc. The letter “I” is not used, so a Decem- C ber built turbo carries an “M” designation. G * Type: A “1 ” indicates a new unit. A “2” indicates a repaired and returned machine. A “3” indicates a Unit Exchange (UTEX) turbo. c c * Plant: There are three plants involved in the assembly of turbochargers. 1 = LaGrange, 11. 5 = Halethorp, Md. 6 = Commerce, Ca. G * Sequence: The last three digits of the serial number indicate the sequence number c; of turbos built at a specific plant each month. The “005” in the exam- ple indicates that the turbo was the 5th one built at the LaGrange G plant during the month of January, 1988. G c Identification Code G The identification code indicates the turbo model, gear ratio, and most recent significant change or revision from the original design which was in effect at the time G that the turbo was assembled. For example: c 3E 17.9 R G Model Ratio Revision G Model: E = 645 Engine Turbo; T = 567 Engines; G = 710 Engines C G Ratio: The gear ratio of the turbo with respect to engine crankshaft speed. An 18 indicates that the turbo runs at 18 times the crankshaft speed. 16.8:l c and 17.9:l are also common gear ratios. G Revision: There have been several revisions or improvements incorporated into the turbo since its inception. The letter code designates the latest revision G which was applied to the turbo. G 0 0 G c - ITS Locomotive Training Series Student Text 7-3 I c,  03 Doweling Assembly 3 The doweling assembly forms the backbone or casing for all the turbo’s internal components. The assembly is comprised of 6 iron castings, which are 3 aligned to one another by dowels and held together by various threaded fasteners. d The alignment of these parts is critical, and the bore through which the turbine wheel passes is held to a maximum of.0005 t.i.r. Consequently, during manufac- kJ ture, the six pieces are aligned and then doweled to maintain that alignment. Next, they receive stamped “doweling numbers” which identify them as a matched set. lu) In the event that one of these components becomes damaged during the life of the turbo, a new part must be aligned to the remaining set components. This new part will then receive a matching doweling number to identify it as part of the original set. Figure 7-3 Turbocharger Doweling Assembly The doweling assembly is comprised of the following: 1. COmpressor Scroll - Forms the scroll through which compressor air flows from the turbine wheel to the engine. 2. Compressor Bearing Support - Provides a location point for the turbine wheel compressor-end support bearing. (Also forms the rear half of the air scroll.) m 7-4 Electro-Motive Model 567.645 & 710 Series Diesel Engines rl(L G c1....... ,.,. __... c‘ c/ ci 3. Turbine Bearing Support - Provides a location for the rotating assembly c turbine-end support bearing. (Also contains the planetary gear system on all turbos and the overrunning clutch on 567 and 645 turbos.) c c1 4. Main Housing - The central component to which the others attach. c 5. Idler Gear Support - Attaches to the “back of the turbo and contains various threaded holes for the attachment of the external gears which 6 connect the rotating assembly to the engine gear train. c 6. Carrier Bearing Support - Provides a location for the roller bearing G which is used to support the planetary gear carrier shaft. c c;; c c G c c G c 0 cI/ c 0 c 6; 5 c c c c cd c, G c ITS Locomotive Training Series - Student Text ~~~ --m c=. Ir-  Main Housing “Cradle”Gasket Area The gasketed surface between the main housing and compressor bearing support (which is known as the “cradle”) was changed from its original 3-piece conventional gasket design to incorporate improved sealing technology. The area which requires sealing is an oval-shaped oil drainage passage at the. bottom of the “cradle”. The original configuration utilized a paper-type gasket at the bottom one-third of the cradle sealing the opening. O n each side of the paper gasket was another made of metal shim stock. These 2 metal gaskets were not required for sealing purposes, but rather were necessary in that their thickness matched the compressed paper gasket thickness. Consequently, the metal gaskets served to maintain parallelism between the two doweling components when the paper gasket was installed. Due to the unfavorable environment in which the cradle gasket was located (heat and vibration), a more durable seal was desired. In the late 1970’s a revised sealing arrangement was released. The turbo main housing oil drain hole was changed from an oval shape to a double round hole configuration with counterbores for O-rings. The 0- ring type turbos required no gaskets between the main housing and compressor bearing support. In order to improve the seal on older castings which were made with oval-shaped openings, a new seal was developed. This seal, known as the “Parker Seal”, is equipped with an oval-shaped O-ring on each side of a metal plate. The seal is retained by two of the doweling assembly through bolts. These improved seals can be applied to most turbos utilizing the oval oil drain configuration by simply machining a relief in the cradle flange of the turbo main housing during overhaul. Figure 7-4 Original 3-Piece Cradle Gasket Figure 7-5 Parker Seal (Model Code Designations Prior to “R”) (,” Model Code Designations) I7-6 Electro-Motive Model 567,645 & 710 Serles Diesel Engines C c , :..--. :...:..,....:Pr..... I ,. '.? , , '. G €4 c c c; c; c c c c; c Figure 7-6 Double 0-Ring Application G ("Wand Later Designations) c; Turbine Wheel c The turbine wheel or rotating assembly as it is sometimes called, is the heart G of any turbocharger. It is comprised of a shaft, on which both the turbine blades c (exhaust fan) and the impeller (air compressor fan) are located. The shaft is sup- ported near each end by 2 support bearings. The bearing nearest the impeller is CJ called the compressor bearing, and the one nearest the turbine blades is known as the turbine bearing. O n the EMD turbo, a small gear is located on the extreme end c of the shaft near the turbine blades. This gear, in conjunction with a series of others, c provides the connection of the turbine wheel to the engine crankshaft as previously discussed. T h e balance of the rotating assembly is extreme+ critical in order to G ensure that vibrations which might occur at the high rotational speeds are mini- mized. G Beginning at the impeller-end, the components of the rotating assembly are c as follows: G 1. Impeller Retaining Nut - Plastic insert type. e 2. Retaining Washer - Secures impeller on shaft. ci c 3. Compressor Impeller - An aluminum castings (forging on 710 model) which contains the blades used to pump air. Blade quantities: G 567 & 645E/EB Models - 16 Blades G 645EC & 645FB Models - 22Blades G 7 10-G Models - 34Blades c (c; 0 G c; c ITS LocomotiveTraining Series -Student Text 7-7 I G A I m  Figure 7-7 lmpeller Design Comparisons 4. Impeller Spacer - A machined washer which acts as a portion of one of the 3 air seals along the rotating assembly shaft. 5. Compressor Bearing Journal - The finished surface on the compressor portion of the shaft which corresponds to the compressor bearing. 6. Heat-Dam Washer - A large washerldisc featuring lands on the surface which contact the turbine wheel to minimize metal to metal contact, thus reducing heat transfer from the turbine wheel to the bearing surface. 7. Compressor Seal - A machined surface on the turbine wheel which acts as a portion of the‘second air seal along the rotating assembly shaft. 8. Turbine Wheel - The central hub of the rotating assembly, on which all the turbine blades are located. 9. Turbine Blades - The blades which collect the exhaust gas flow and cause the rotating assembly to turn. Numbers of blades: 567 & 645 All Models - 47Blades 710-B Models - 53 Blades 10. Sun Gear Shaft - The rotating assembly shaft is actually split into two parts. The turbine wheel forms the “front” end, containing the impeller and turbine blades, while the sun gear shaft forms the “rear” end. The sun gear shaft comprises 3 distinct components. a. Turbine Seal: A machined surface on the shaft which acts as a portion of the third air seal along the rotating assembly shaft. b. Turbine Bearing Journal: The finished surface on the turbine- end of the shaft which corresponds to the turbine bearing. c. Sun Gear: A gear which is a part of the sun gear shaft, and acts as the central gear in the planetary geardrive system. 7-8 ElectrMotive Model 567, 645 & 710 Series Diesel Engines G c c G c c G G c G Impeller Nut ' /' Heat Dam ii Washer G I I / '\ 1 G G G ' I Sun Gear Shaft G I G Turbine Wheel Assembly Lr (Including Turbine Blades c. And Blade Retainers) G Figure 7-8 Rotating Assembly c G G G C G c G c c G G G G G F v 7-9 Rotating AssembZy G G G 0  Turbocharger Bearings As previously discussed, the rotating assembly is supported by two bearings which are located in the doweling assembly. Due to the high speeds and temperature levels that the turbine wheel is exposed to, the design and construction of these bearings is rather unusual. Both the compressor journal bearing and the turbine journal bearing are designed with cylindrical tapers which form oil wedges that develop powerful radially oriented hydraulic forces to center the rotating journals. Thus, rather than using a concentric bore on the inside diameter of the bearings, oil “ramps” are utilized. The hydraulic forces developed in the journal bearings and thrust bearing far exceed the engine lube oil pressure. Also, because these forces are generated by the rotating journals, the hy- draulic forces increase as rotor speed increases. There may be 3,4, or 5 ramps on the inner surface of the rotating assembly support bearings. Each ramp begins at an oil “channel” or groove. The distance from the surface of the bearing to the journal is greatest at this point. As the ramp extends around the inside of the bearing, its height increases and the clearance between the bearing and the journal decreases. The difference in ramp “height” from the low-end at the oil channel and the high-end is approximately.003-,004”. The lubricating oil which is pumped into the bearings is drawn along the oil ramps by the rotation of the turbine wheel. As this oil flows along the ramp, the bearing clearance decreases, which increases the centering force exerted on the journal. This is known as a “hydra-dynamic” bearing design. 1. Compressor Bearing: The hydra-dynamic bearing through which passes the impeller-end of the rotating assembly. The compressor bearing supports the compressor portion of the rotating assembly shaft. The inboard end of the compressor bearing is flared and manufactured with a convex surface to form a part of the thrust bearing assembly. The compressor bearing is located in the compressor bearing support, and is retained by an interference fit. 2. Thrust Bearing: A disc-shaped bearing through which the turbine wheel shaft also passes. One side is concave to correspond with the flared end on the com- pressor bearing. These curved surfaces permit a self-aligning feature. The opposite side of the thrust bearing appears flat, but actually consists of a series of tapered pads on the thrust face which form oil wedges that develop hydraulic pressure to separate the bearing from the rotating heat dam thrust washer. 6 4 s The thrust forces found in the rotating assembly are caused by the pitch of the impeller blades. These blades are shaped to pull air through, similarly to the propeller on an airplane. Unlike the airplane, which uses this concept to pull the machine through the air, a turbocharger impeller must remain stationary to pump the air through its compressor section. 21 7-10 ElectrcMotive Model 557.645 & 710 S w k s Diegel Engine8 G c u -....- -. c.. __.I......,. G (;I It is the function of the thrust bearing to control the tendency of the turbine c wheel to move forward. Exhaust pressure against the wheel also contributes to the load the thrust bearing must control. The thrust bearing is located c between the flared edge of the compressor bearing and the heat dam washer c on the turbine wheel. c 3. Turbine Bearing: This bearing supports the 2un gear end of the rotating assembly. Its construction is similar to that of the compressor bearing, G except that it does not have the flared edge. The turbine bearing is located c in the “clutch support”, which in turn is located in the turbine bearing support. c 4. Planet Gear Bearings: A set consisting of three identical bearings, one for c each of the 3 planetary gears. These bearings differ from those previously discussed in that the oil ramp is on the outside diameter of the bearing. G One bearing is installed in the bore of each planet gear, and the gears rotate c on the stational? bearings. e; c Pin Hole G c; G PLANET GEAR BEARING G Pin Engagement Notch c c COMPRESSOR BEARING c c G c THRUST BEARING TURBINE BEARING Figure 7-10 Turbocharger Bearings G G Turbocharger Labyrinth SeaIs I 6: The seals usedin the turbo utilize air pressure as the a c b d seal. No physical G contact between the turbine wheel shaft and the seal occurs. Instead, pressurized air from the compressor scroll is ported to three “labyrinth” seals through a “bleed” air c duct. Once in the seals, the air emits from a small hole in the bore through the center of the seal. This bore, through which the rotating assembly passes, contains G several grooves or “labyrinths”.The air flows around the seal in these grooves, G effectively sealing the area. C G - ITS Locomotive Training Series Student Text 7-11 0 I l r.  3 3 anet iaring 4d Planet 3 Carrier 1 Assembly 3 GEAR DRIVE SECTION 3 3 Figure 7-1 1 Turbocharger Bearings 6.Labyrinth Seals 3 3 These seals are effective at separating the lubricating oil from the exhaust gases. 3 However, improperly filtered air can form dirt deposits within the air passages, which kJ l will restrict the air flow and reduce the effectiveness of the seals. There are 3 labyrinth seals in the EMD turbo. CrJO 1. Impeller Seal: Located directly behind the impeller, this seal prevents oil in u the compressor bearing area from being drawn out into the compressor air 3 scroll by the suction created as the impeller spins. lr3 2. Compressor Seal: This seal is located between the turbine blades and the compressor bearing. Its function is to prevent oil from migrating into the 3 exhaust section from the compressor bearing. 19 3. Turbine Seal: The turbine seal is located between the turbine blades and 3 the turbine bearing. It prevents oil from migrating into the exhaust duct from the turbine bearing..Irs -)d 7-12 ElectroMotive Model 567,645 & 710 Series Diesel Engines Ls - a W l c.... ,.... G ci c c c G G c c c c TURBINE SEAL G c c G c G c G G COMPRESSOR SEAL G G C c G G G c G IMPELLER SEAL Figure 7-12 Turbocharger Labyrtnth Seals C G G G G ITS Locomotive Training Series - Student Text 7-13 I & 1  Turbine Inlet Scroll The high-energy exhaust gas is deliverecl to the single-stage turbine by the exhaust inlet scroll. This component is a welded assembly made from “chrome- moly” plate which is formed so that the incoming gas flow is smoothly and evenly distributed with a minimum of turbulence. t-xA p;ff ’ Figure 7-13 Turbine Inlet Scroll 6 Nozzle Ring Nozzle Ring The nozzle ring is located in the exhaust portion or turbine section of the machine. The nozzle ring consists of a series of stationary vanes through which the exhaust gas from the engine must pass in order to reach the turbine blades. Each passage between the vanes is called a nozzle. The nozzle ring is therefore simply a ring of individual nozzles which are mounted on a common ring. The gas is throt- tled and directed by the nozzles into the turbine wheel blades. The size of the nozzle openings must be matched to the amount of exhaust gas generated by the particular engine that the turbo is designed for. Larger passages are found on nozzle rings for larger engines, etc. This is due to the fact that larger engines flow a higher exhaust gas volume than do small ones. Consequently, a small nozzle ring would choke a large engine’s exhaust gas flow. Conversely, a large nozzle on a small engine would not provide enough restriction for the gas flow to develop the correct amount of velocity as it flows through the passages. rd..y*..L. r The principle may be more easily understood if compared to a garden hose %I 7.1’ 19 nozzle. As the nozzle opening is decreased more energy or force is obtained from the flow of the water. In the turbocharger, the optimum nozzle opening is just 3 enough to allow an engine’s maximum exhaust gas volume to pass without creating a back-pressure. If the gas cannot flow through the nozzle quickly enough, it will 3 begin to “back-up” in the exhaust system and the turbo will eventual1 “sur e”. The 5+ term surge refers to a reversal of the gas flow through the turbo. The mac ine actually “burps” exhaust back through the engine due to a greater pressure within ‘cr) ) 3 the engine or exhaust system than that of the incoming air supply. 3 7-14 Electro-MotiveModel 567,645 & 710 Series Diesel Engines us c3i __ C c.... G G G Turbine Shroud and Retaining Clamp G The turbine shroud is a metal band which encircles the turbine blades. Because c the turbo’s power is generated by the exhaust gas between the blades, high efficiency is obtained by minimizing leakage around the c blades. Consequently the turbine shroud is c formed around the blade tips on the turbine wheel. The shroud’s function is to ensure c that the exhaust gas flow across the turbine blades is maximized by reducing gas leakage c around the blade tips. G The blade tip to shroud clearance c must be small enough to minimize gas leakage, but large enough to prevent contact c with the blade tips as they enlarge through thermal growth. For this reason, the inside c diameter of the EMD turbine shroud is Figure 7-14 Turbine Nozzle Ring G sprayed with a “soft metal” abrasable coating. The blades can actually establish their own e path in this coating as their temperatures normalize, creating a custom-fitting shroud for each individual turbo. c c The shroud is retained (in most turbo models) by a clamping ring known as the “Marmon Clamp”. This clamp consists of a metal band, to which 4 channel segments c are spot-welded. The channels engage a flange on the edge of the turbine shroud, securing it within the turbo. A “T-bolt” and nut are used to apply clamping load to.the c assembly. G An improvement was made to the Marmon clamp in the early 1980’s. Prior to this G improvement, the strap to which the T-bolt is attached was spot welded to the clamp. Tests in the field indicated that the clamp could suffer from metal fatigue in the area c adjacent to these welds after repeated thermal cycling. An improved clamp was released which utilizes rivets to secure the T-bolt strap. This clamp has proven more durable in c severe service applications. c G G G c e c G Figure 7-15 Turbine Shroud and Retainer G c c - ITS Locomotive Training Series Student Text 7-15 a G  Exhaust Diffuser The exhaust diffuser is another aerodynamic device located in the turbine section of the turbo. The diffuser is basically an arrangement of 3 or 4 vanes (stationaryfins) which are placed directly behind the turbine blades. As the exhaust gas flows through the turbine blades, it next must enter the turbo’s exhaust duct. In order to direct this flow of gas from the blades smoothly into the duct, the diffuser vanes provide a smooth transition path for the gas to follow, thereby eliminating turbulence. Figure 7-16 Turbine Shroud Retainer, Exhaust Exhaust Duct D u d and Exhaust Difiser The exhaust duct acts as the outlet for the engine’s exhaust gas after it has passed through the turbine blades. The duct “floats” to allow for thermal expansion and is mounted with bolted spring washers located along a mounting “foot” on each side where it rests on the main housing. The duct is sealed to the turbo by means of a half-lap joint and retainer ring on the compressor bearing support side and two spring-tensioned seal rings at the inlet scroll end. There are two basic exhaust ducts which are applied to the EMD turbo, The “standard” duct is attached to the turbo main housing by 3 spring washer sets on each mounting foot. This duct was used on most applications until the late 1970’s.The other basic duct, known as the “big-foot” duct, is two inches shorter than the standard duct, and is attached to the turbo by 5 spring washer sets on each mounting foot. This duct was designed for the application of an exhaust silencer atop the turbo duct, and is therefore made shorter and is heavily reinforced to support the added weight. A built-in aspirator tube provision in both ducts allows for the installation of an “eductor tube”, which produces a suction that is applied to the engine crankcase for ventilation. As exhaust gas flows upward and out of the duct, a negative pressure is established behind the beveled end of the tube. The outboard, flanged end of the tube is connected tewarfidter which contains a screen called the lube oil separator. - The suction applied above the screen in the separator draws vapors from the engine crankcase, while the screen prevents lube oil from being drawn out. Locomotive applications which utilize an exhaust silencer, as well as most marine and industrial applications, use an “ejector‘ arrangement. This system uses compressor discharge air directed through a venturi and combined with the eductor tube suction to aspirate the crankcases of these engines which have inhibited ex- haust gas flow due to restrictions such as silencers or long runs of exhaust ductwork. 7-16 ElectroMotive Model 567.645 81710 Series Diesel Engines G c - -.......... ~.... G G G A drain opening is provided near the bottom of the duct to allow for the drainage G of rdinwater which may enter the duct while the engine is shut-down. This drain hole location corresponds with a small tube that passes through the compressor bearing G support from the impeller side. The drain hole is of a larger diameter than that of the tube. When the impeller is spinning, pressurized air is blown through the tube, and into G the duct drain. This pressure, being greater than the exhaust gas pressure in the duct, G effectively prohibits gas leakage through the drain. However, when the impeller is not in operation, no air pressure flows through the tube. In this case, the drain hole in the duct Ifi will allow any fluids which have collected in the exhaust duct to drain into the turbo main housing, which has a corresponding hole near the bottom for further drainage out (5 of the entire turbo. G G c G c d, c CI c L G G G Low Profile Duct Tall Duct G 6/ Figure 7-17 Exhuust Duct c C G. Gi c G @ G G c ITS Locomotive Training Series - Student Text 7-17 I 0  3 3 e) COMPRESSOR DIFFUSER The compressor diffuser consists of a row of fins or (‘vanes’’which are attached to a mounting ring and positioned around the circumference of the 3 impeller. The vanes direct the flow of compressed air which is discharged from the impeller and provide a smooth air delivery which is free of turbulence. The 3 compressor diffusers are manufactured with specifically sized “throat passages” 3 between the vanes. The size of these passages controls the air flow so that the compressor power requirements are balanced with the power generated in the 3 turbine by the exhaust gas energy at full load. For this reason, the compressor diffuser throat area must be “matched” to the turbine nozzle ring area during u turbo assembly. d These throat passage sizes also 3 correspond to the volume of air that the turbo supplies. For example, a turbo for a 3 16 cylinder engine contains a diffuser with larger throat passages than one designed for use on a 12 cylinder application. Figure 7-18 Compressor Diffusers Figure 7-19 Compressor Diffusers m 7-18 Electrdvlotive Model 567,645 81710 Series Diesel Engines G c G c Q PLANET GEARS G The sun gear which is machined onto the end of the turbine wheel meshes with G 3 planet gears. These gears engage with the sun gear at 120 degrees intervals, and are located by a planetary gear carrier shaft. The carrier shaft is basically a disc, from the face G of which extends 3 pins. Each pin passes through the center of a planet gear. O n the c opposite side of this disc, the carrier shaft itself is splined. G There are two basic planet gear designs: the original or “standard” 32 tooth gear and the “high-capacity” 47 tooth gear. It is a fact that all gears transmit a vibration as their c, teeth mesh. The level of vibration varies with such things as wear, roughness, and tooth c profile. The original configuration planet gear set performed satisfactorily in the rail applications for which it was designed, but when EMD turbocharged engines began to c see service in high gear-loading applications such as generating set installations, a more durable gear design was desired. c Generating sets, for example, are subjected to constant high rpm regardless of the c amount of load on the system. This constant speed is necessary in order to maintain the G electrical “line frequency”. Such engines often run at less than full rated load. Conse- quently, exhaust gas energy levels are lower than normal, which means that the turbo c gear drive must make-up for the less powerful exhaust. The end result of continued operation in this mode is accelerated planet gear wear. c Worn planet gears can cause seriously increased gear vibration levels. The in- G creased vibrations in the planet system cause the turbine wheel to vibrate. This vibratory c input results in turbine blade fatigue fractures in worst-case situations, and rapid clutch wear in many cases. The solution to the problem is to reduce the vibration level gener- c ated by the gear mesh by increasing the tooth to distribute loading over a larger area. c These “high-contact” or “high capacity” gears significantly reduced the light-load vibra- tory levels, and tooth wear was nearly eliminated under high gear train loading condi- ci tions. C Usage of the high-capacity gear train has spread over the years from marine drilling applications only to marine propulsion, industrial generator sets, and rail engines as well. c Turbos utilizing the standard gear design carry 18:l or 19.7:l gear ratio designa- G tions.Those which contain the high-capacity gears utilize ratios of 16.7,16.8,or 17.9:l. G In any case the ratio designation refers to the speed differential between the turbocharger impeller and the engine crankshaft. c, G &. G G c G G ii IlS Locomotive Training Series -Student Text 7-19 I  RING GEAR AND CLUTCH HOUSING The third element in the planetary gear tralli is the ring gear. The ring gear surrounds the 3 planet gears, and is manufactured with internally cut teeth on the inside diameter. Consequently, each planet gear’s teeth are actually engaged to 2 gears simultaneously: 1) the sun gear on the turbine wheel shaft 2) the ring gear which surrounds them. T h e ring gear is attached to a housing which encases the turbo clutch. The means of this attachment are bolts, so the ring gear is locked to the clutch housing. This clutch housing is located within the turbine bearing support (part of the doweling assembly), and rotates on the outside diameter or the clutch support (where the turbine bearing is located). Bronze thrust washers and bushings are used as bearing surfaces between the clutch support and the clutch housing. Figure 7-20 Ring Gear and Clutch Housing 7-20 Electro-MotiveModel 567,645 & 710 Series Diesel Engines c c G e c CLUTCH CAMPLATE AND ROLLERS c The overrunning clutch design allows rotation in one direction, and engagement 6 or “lock-up” in the other. This is accomplished through the use of a center hub called the support, a set of cylindrical rollers, and a surrounding ring called the camplate, c which utilizes a series of wedge-shaped pockets in which the rollers are located. c The 12 pockets in the camplate are designed with an angled ramp in each. Thus, c the distance from the outside diameter of the support to the ramp varies depending on where the measurement is taken. This pocket depth at one end of the ramp is greater c than the diameter of the roller. However, at the opposite end of the ramp, the pocket c depth is less than the roller’s diameter. Consequently, when the roller approaches this end, it becomes wedged between the support and the camplate ramp, locking the c two parts. c c c c c c c c c r I..........-... ‘t- -. 7” \ I c Figure 7-22 Clutch Camplate c; C On the example below, note that if the camplate were rotated in a clockwise direction, the rollers would move into the large ends of the camplate ramps, allowing the G camplate to rotate free of the support. However, if the camplate were turned counter- clockwise, the rollers would travel to the small ends of the ramps and effectively lock the c camplate to the stationary clutch support. c The camplate is located in the clutch housing, on the end of which is also found c the ring gear. The camplate is attached to the clutch housing by means of 6 “drive pins” or dowels. As a result, the camplate and ring gear operate as one unit, each one being c attached to the clutch housing at opposite ends. c Since the clutch support is stationary in’the turbo (being bolted to the turbine G bearing support), when the camplate locks to the support, the clutch housing and ring gear also become locked. G c c c ITS Locomotive Training Series -Student Text 7-21 I G  T I W ’ GEAR DRIVE SYSTEM The splined-end of the carrier shaft extends through the idler gear support, which is the plate at the back of the turbo. Two bearings are used to support the carrier shaft: 1) a ball bearing located in the idler gear support; and, 2) a roller bearing which is in the carrier bearing support. O n the splines of the shaft, a carrier drive gear is mounted. This gear is actually externally mounted on the turbo, although most of it is obscured from view by the carrier bearing support. Located on a small stub-shaft attached to the idler gear support below the carrier gear is the turbo idler gear. The idler gear is engaged with the carrier drive gear at the top, and with the engine’s gear train at the bottom. The idler gear is mounted on a special, barrel-faced roller bearing. This bearing has a self-aligning feature due to the barrel-shaped rollers. As a result, the gear can actually be “wob bled” on its stubshaft if force is applied.. : Carriar Shaft Spacer 9. Idler Gear Roller Bearing 2. Set Of 3 Matched Planet Gears 10. Idler Shaft 3. Planet Gear Shafts 11. Carrier Drive Gear 4. Planet Gear Bearings 12. Carrier Shaft 5. Carrier Shaft Retainer Plate 6. Carrier Shaft 13. Carrier Gear Ball Bearin Roller Bearing 7. Idler Gear #upport 14. Lube Oil Jumper 8. Idler Geer Assepbly 16. Carrier Bearing Support Figure 7-23 Gear Drive Section m 7-22 Electro-MotiveModel 567,645 & 710 Series Diesel Engines v I G c G c c GEAR-DRIVE SYSTEM c Right-Hand Drive Applications: G Some marine propulsion applications of EMD engines employ two counter- c rotating engines. In such installations, a pair of engines, one left-hand rotating (standard) and one right-hand rotating share a common hull. Since the gear train of the right-hand c rotation engine turns in the opposite direction from that of the standard engine, a special c turbocharger is required. The turbo for use on these right-hand rotation engines utilizes two turbo idler gears rather than the single gear on more common models. In this way, c even though the engine gears turn in the opposite rotation, the turbine wheel is driven in the same direction on all EMD turbochargers. c C c c c e G G LEFT HAND ROTATION RIGHT HAND ROTATION c GEAR TRAIN Figure 7-24 Gear Drive Systems GEAR TRAIN c LUBE OIL SYSTEM c The turbocharger’s lubrication system is actually an extension of the engine oil c system. Following is a description of flow: G 1. As oil travels through the main oil gallery in the crankcase towards the rear c of the engine, it enters the stubshaft bracket assembly on the end sheet of the engine. c 2. An oil passage or groove in this bracket directs the oil to an oil manifold G which is also attached to the end-sheet. The oil flows through the manifold c and is delivered to the turbo oil filter mounted on the engine. c 3. Oil flows through this filter, which carries the same rating as the filters in the main filter tank. G 4. Provided the filter is not plugged, oil leaves the filter and flows back G through the lower leg of the oil manifold. Note: If the filter is plugged, no G oil will flow through the small oil pressure sensing line which connects the engine governor to the downstream side of the turbo filter. G 5. Oil flows through another grooved passage in the engine stubshaft bracket c; and is admitted to the upper idler stub. G c ITS Locomotive Training Series - Student Text 7-23 c  3 6. Oil flows through a passage in the center of the stubshaft into the 4- inch bore in the turbo main housing. 7. A vertical passage in the turbo main housing called the “main oil kib supply” directs the oil upwards. 3 8. The main oil passage emits oil at the top for the clutch and planetary gears. A branch line from the main passage passes through the main housing carrying oil to the auxiliary generator drive and also intercon nects to the compressor and turbine bearing lines. cr) SOAK-BACK SYSTEM 03 Due to the fact that the turbo is dependent upon the engine main oil system, u an additional lubrication system is required to protect the turbo during those periods 3 when main oil system flow is unavailable. ti4 The main oil system is driven by a gear train connected to the crankshaft. 3 Consequently, oil flow is present only when the crankshaft turns. During an engine shutdown, the crankshaft continues to turn for 5-10 seconds after the shutdown is 3 triggered. However, due to the high speed at which the turbine wheel operates, the momentum of the mass causes the turbine to “run down” for periods as long as 35- 40 seconds. Consequently, no lubrication is provided to the turbo’s bearings by the I main oil system during this time. UJD 3 As a result, an electrically-driven oil pump called the “soakback Pump’’ is mounted on the engine to provide lubrication to the turbo during this rundown 3 period. As the engine shutdown cycle occurs, the pump is energized and begins to supply the turbo with oil. After the engine stops, the soak-back pump continues to 3. heat operate for 30-35 minutes. During this time, the flow of lube oil is used to carry 3 from the turbo’s seals and bearings(hence the name “soakback"). The soakback pump is also energized during the engine start sequence. In this instance, the bearings in the turbo are supplied with oil even before the oil flow from the main system can reach them. In this way the soakback pump serves to pre- lubricate the bearings. 7-24 EiectroMotive Model 567,645 & 710 Series Diesel Engines C c..-....... c G c c G c c t c c G c L c c 55011 c c c c G Figure 7-25 Turbo Lube Oil System G c PLANETARY SYSTEM OIL DRAINAGE SCREEN G Lube oil drainage from the planetary system of the turbo passes through openings G in the idler gear support. In the event of a planetary system failure, metal fragments and G broken gear teeth may be carried-off with oil drainage. To prevent these metal fragments from entering the engine oil sump or passing through the diesel engine's rear gear train, c a screen is installed in the idler gear support. c The original screen was located in a small triangular-shaped opening in the idler c gear support. Most planetary system drain oil flows through this area. However, turbos which are equipped with the highcapacity type planet gears have a higher oil flow rate c which requires an increased oil drainage provision. The idler gear support on such turbos utilizes three slotted passages on the face of the support in addition to the triangu- G lar opening. Drain oil flows through all four of these passages. Consequently, it is neces- $1) + _i. sary to provide increased protection in the way of a larger screen. G G In the mid-l980's, an improved screen was released for retrofit in the high-capac- ity turbos. The screen is installed on the inboard side of the idler gear support, and oil G must pass through it as it flows through any of the four possible drainage paths. Turbos so-equipped do not utilize the previous triangular screen. G c c ITS Locomotive Training Series - Student Text 7-25 a c  GEAR TRAIN OPERATION The EMD turbocharger utilizes a geardrive system which takes energy from the engine’s crankshaft and transmits it to the turbine wheel at the sun gear. This planetary gear drive system is used when exhaust gas energy levels are not sufficient to drive the turbine wheel, such as during engine starting and low speedflight load periods of operation. Dependency on the gear drive system decreases as exhaust energy levels increase, until eventually no mechanical assist is required. It is the function of the overrunning clutch to “disengage”the gear drive. This is accom- plished by allowing the rotating assembly to overspeed the driving gear train while the gears remain engaged. This power take-off originates at the upper idler gear in the engine’s camshaft drive gear train. This upper idler gear is equipped with a shock damping device which uses packs of coil springs to absorb torsion shocks in the engine’s gear train. Attached to this damping device is a turbo drive gear. The turbo drive gear, which serves as the power take-off for the turbo’s gear train, is isolated from the inherent engine torsional vibrations which can be detrimental to the turbo’s longevity. Figure 7-26 Spring Drive Gear The next gear in the turbo gear train is mounted on the “rear” of the turbo at the idler gear support. This gear is appr0priate.j named the turbo idler gear. The idler gear drives a turbo-mounted carrier shaft drive gear. This gear is located on the end of the planetary gear carrier shaft. The carrier shaft extends through the rear “bulkhead” of the turbo and carries the 3 planetary gears. The planet gears are engaged to both the sun gear on the end of the turbine wheel, and to a ring gear. The 3 planet gears surround the central sun gear, Obeing meshed with the sun at 120 degree intervals. These planet gears are also surrounded by a ring gear. The ring gear is manufactured with internal teeth, so that a “track” is formed on which the 3 planet gears can travel. The ring gear is attached to the clutch camplate, and the two components operate together as one. If the camplate rotates, so does the ring gear. Conversely, if the camplate is locked, the ring gear cannot move.. T I To understand how the engine gear train drives the turbine wheel, a simu- lated engine start-up sequence follows: 1. As the starter motor pinions engage the flywheel, the crankshaft is rotated. II 7-26 Electro-MotiveModel 567,645 & 710 Serbs Diesel Engines e c G c c 2. The lower idler gear in the camshaft gear train is turned by the force G transmitted from the gear teeth on the crank gear to those on the lower idler. c 3. The lower idler gear teeth transmit force to the upper idler gear teeth G which they engage with, turning the upper idlerhpring-drive gear ass G embly. c 4. The turbo drive gear (on the spring-drive gear) assembly transmits force to the teeth of the turbo idler gear. G c 5. The turbo idler gear teeth turn the carrier shaft drive gear. c 6. The carrier drive gear turns the entire carrier shaft assembly. e 7. The 3 planet gears located in the rotating carrier shaft pass the torque on c to both the sun gear and the ring gear. c 8. The torque input to the ring gear turns it (and the clutch housing) in the opposite direction. However, after a very short travel the camplate locks c to the clutch support due to the rollers which have become wedged in the ramps. c 9. With the ring gear held stationary, gear train torque is transmitted C through the planet gears to the sun gear. This causes the sun gear to c drive the turbine wheel (in a counterclockwise direction as viewed from the impeller). Due to the speed-increasing nature of a planetary gear C system, the sun gear’s rotational speed is significantly higher than that of the carrier shaft assembly which drives it. G c 10. As the impeller is rotated, air drawn through the engine filters increases in velocity while passing through the compressor di&ser and air scroll c with a minimum of turbulence. The size of the passages in the compres sor d i h s e r controls the air flow so that the compressor power require C ments are balanced with the power generated in the turbine by exhaust gas energy at full rated load. (It is for this reason that the compressor G diffuser throat area must be “matched” to the turbine nozzle area when e the turbo is assembled.)’ c 11. As air is pumped into the engine, the combustion process begins. As the c engine runs, the exhaust gases from the individual cylinders are directed through the turbine section of the turbocharger. The energy extracted c from these gases is applied to the turbine blades, and this force aids the engine gear train in turning the rotating assembly. c 12. Two sources of torque are fed into the planetary gear system. The torque G developed by the turbine is fed through the sun gear, and the torque c transmitted by the gear train is fed through the carrier shaft to the planet gears. Thus, the torque transmitted to the ring gear is the difference G between the levels of the two torque inputs. c c ITS Locomotive Training Series - Student Text 7-27 C... : I. I -... r 3 ,..--. -.. 13. When the turbine does not develop sufficient power to turn the rotor at the enginedetermined driving speed, the torque input through the planet gears continues to hold the ring gear and camplate in the “locked”direction as previously described. However, when the power developed in the turbine is capable of driving the rotor faster than the speed dictated by the turbo gear ratio, the increased torque from the sun gear is fed through the planet gears to rotate the ring gear and camplate in the “unlocked”direction. The clutch housing now rotates around the clutch support at a speed and turbine wheel RPM.During this overrunning condition, the clutch rollers are in the wide end of the wedge-shaped pockets formed by the camplate ramps. 14. The turbo continues to operate in this “free-wheeling” state so long as the exhaust gas energy level and flow rate are sufficient to provide enough power to drive the rotating assembly faster than the gear train would. However, if the engine speed or load is reduced, the amount of energy in the exhaust decreases, and the turbine speed begins to drop. When the turbine speed returns to that of the gear train, the clutch re- engages and the gear train once again provides a portion of the energy , requirement to drive the rotating assembly. TURBOCHARGERS WITH EXTERNAL CLUTCH All 567-T and most 645-E/F turbos utilize the internally located 12 roller clutch design as discussed. However, in the early 1980’s an experimental “external clutch” was field tested in selected applications where loads on the conventional clutch were severe. These tests were conducted with 645 turbos primarily in marine towing service. The external clutch became “basic” or standard equipment with the 710-G engine. This design removes the clutch from within the turbo and places it in the engine camshaft drive gear train instead. The spring-drive gear assembly found in the previous 6 4 5 series is replaced with a new double gear assembly which is inter- connected by means of a large version of the roller clutch configuration. The clutch utilizes 16 three-quarter inch diameter rollers in place of the 12 one-half inch diameter rollers found in the internal clutch. The new rollers are one and one-half inches long, whereby the 12 roller clutch used one inch long rollers. Correspondingly, the camplate diameter of the external clutch is approximately 11.750” compared to the 7.750” of the previous type. Also, the camplate roller pockets are inverted, or open towards the outside diameter rather than toward the center of the p+$ q OE previous versions. The increased size of these components, coupled with the more numerous rollers, has improved the load-carrying characteristics of the roller clutch tremen- dously. 7-28 ElectrMotive Model 567,645 & 710 Series Diesel Engines e; G G c c The principle of operation is exactly the same as that of the internal clutch. However, G since the clutch disengagement takes place in the engine gear train, the turbo’s plan- etary ring gear is now “locked” in a stationary position. This lock-up device occupies the c space where the roller clutch had been on previous turbo models. c The clutch support has been modified from its original configuration with the c addition of a row of gear teeth. The outside diameter of these teeth is the same as that of the three planet gears in the carrier shaft assembly. The ring gear is now much longer c than its predecessor, with two rows of identical teeth cut on the inside diameter. This new ring gear bears a resemblance to a sleeve such as is used to synchronize gears in c automobile transmissions. The clutch support teeth enter the ring gear at one end, and c the planet gears from the other. Since the clutch support is fixed in place, its tooth engagement with the ring gear prevents rotation of the ring gear. G Although not a common practice, the external clutch can be applied to 645 type c turbos equipped with high-capacity planetary systems. c c1 c L TU~U~J Drv ie, Clutch Drive sumn ~ - y/ Cam Plate ~ Upper Idler Gear Assembly c c 1/2”-20 Hex Bolts - C 3/8-24 Spline HD c c c c ci G (;. c Clutch Doweling G c I- \ -1/2” Special Washers c 8 Rw‘d. Camplrrtb Retainer Roller 28.87 0 c Figure 7-27 External Clutch c c ITS Locomotive Training Series - Student Text 7-29 fl G  EXTERNAL INSPECTION AND OPERATIONAL PROBLEM DIAGNOSIS Over the past several years, many items have been written and discussed regarding how to qualify an EMD turbocharger for continued service when a problem has been reported. Many of these techniques have been passed on verbally, while others were written procedures foun‘d in Engine Manuals, Troubleshooting Guides, or various written correspondence. In some cases, these procedures have become obsolete or in need of revision due to the evolution of the turbo, as well as a broader base of practical experience from which to draw on. The following pages are offered to assist EMD customers in troubleshooting and requalifying their turbos. CHECKS WHICH CAN BE MADE WHILE THE TURBO IS STILL ON THE ENGINE A. ROLLER CLUTCH TEST 1. Idle engine until normal operating temperature is reached. (If engine cannot be started, remove rubber boot from turbo inlet and verify that the impeller locks- up when attempting to turn in a clockwise direction by hand. If this does not occur, either the clutch has completely failed or a planetary gear train failure has occurred. Refer to paragraph Additional External Inspections.) 2. With engine warmed-up, push injector control linkage lever inward, increasing engine speed to approximately 700 RPM. 3. Pull injector control linkage lever out completely to “No Fuel” position, overrid- ing the engine governor. (At this time, the clutch will disengage, allowing the turbine to spin free of the gear drive.) 4. As the engine begins to stall, push the injector linkage lever in once again, providing more fuel, which should increase engine speed. The decelerating turbine wheel will “meet” the accelerating eqgine gear train and the roller clutch should engage, providing sufficient air for continued engine speed increase. If the clutch fails to engage, the injector rack linkage will move toward “full fuel” position, black smoke will emit from the exhaust duct due to a lack of air, and the engine may stall. These symptoms indicate an imminent clutch failure, consequently the turbocharger should be replaced. Turbocharger roller-type clutches tend to h i €gradually rather than suddenly. This characteristic refers to the fact that in early stages of clutch wear-out, the slippage may be intermittent. In such instances, the engine may smoke heavily or stall during speed changes, yet behave normally later. T o ensure that the clutch is not in this early stage of failure, the aforementioned test procedure may be repeated a few times. However, articles stating that as many as 30 consecu- tive tests may be required are in error. 7-30 ElectroMotive Model 567, 645 & 710 Series Diesel Engines c c ci G c To avoid damaging a good clutch, injector linkage manipulation should not c be performed more than 2 or 3 times to qualify a clutch. If the clutch is in fact defective, the turbo should exhibit the reference symptoms within this G number of trials. L Since 1976, virtually all regular production 567 and 645 EMD turbos have c been built with a roller-type clutch. Prior to that date, some turbos had utilized a ratchet-type clutch/friction drive gear configuration which required c a special requalification procedure using a torque wrench. Under no circum- stances should a wrench be applied to the compressor impeller nut to deter- c mine roller clutch condition. A test of the older design friction drive gear c called for the application of a torque wrench to the impeller nut. The ob- served “break-away torque” provided an indication of the condition of the L friction drive gear, but no conclusion could be drawn as to the turbocharger clutch condition from this test. Furthermore, this test was valid only on c turbos equipped with the previous “ratchet” clutch. Engines equipped with roller clutch turbos should not be subjected to this procedure. c 0 0 B. TURBOCHARGER OIL PRESSURE TEST G In some instances, it may be prudent to confirm that the main engine and soi--back oil systems are actually delivering lube oil to the turbo. This test would -e c recommended after the installation of a turbo which was not run in a test cell after L assembly by the remanufacturer, or upon installation of a replacement turbo after a “bearing failure” had occurred. Turbocharger bearing failures are usually a result of G an external condition such as an imbalance of the rotating assembly (due to foreign object damage) or to a lack of proper lubrication. Therefore, when an impeller is G observed to be rubbing the inside of the air inlet portion of the turbo and no damage c is observed on the turbine blades, it is wise to confirm the flow of lube oil through the new turbo prior to returning the engine to service. G 1. Locate and remove the compressor bearing oil passage pipe plug on the c right bank side of the engine turbocharger. This plug is installed in the compressor bearing support, which is the 3” thick casting between the main c housing and the air scroll. The 1/2” PT lug accepts a 3/8” male square drive G such as that of an ordinary ratchet wrench. The plug will be found above the right-bank turbo air scroll to aftercooler duct mounting flange. Gd 2. Temporarily install an oil pressure gauge in the oil passage. c 3. Operate the soak-back pump while observing the oil pressure gauge. The C gauge should indicate the presence of oil pressure, typically in the 15-30 PSI c range. (At the same time, check to make sure that no oil is observed flowing from the engine camshaft bearings - this condition would indicate that the c check valve in the turbo filter assembly is defective.) If not oil pressure is observed at the turbo, do not start the engine until the cause is determined. v G c c ITS LocomotiveTraining Series -Student Text 7-31 I 0 A A c c c c G 6. Standing adjacent to the flywheel for viewing, energize a stopwatch at the c moment when the crankshaft is observed to stop rotating. c 7. Listen carefully for the compressor impeller to stop rotating (identified by c the cessation of a whirring sound). Stop the timer immediately. c 8. Due to the momentum of the rotating assembly, the elapsed time should not fall below 27 seconds. Actual run-down times will vary, depending upon c the speed of the rotating assembly at the time of shut-down. However, a time of less than 27 seconds from full-speed/full-load indicates that a condition c exists which inhibits the rotor from turning freely. c c ADDITIONAL TURBOCHARGER EXTERNAL INSPECTIONS c It is fact that 60-75 percent of all “turbocharger failures” are caused from an L external source such as foreign object damage, overheat/overspeed, lack of proper c lubrication, etc. Consequently, unless the damaged turbo undergoes a thorough diagnosis, the condition that existed within the engine which actually caused the c failure cannot be determined. Likewise, unless this undesirable condition is cor- rected, repetitive “turbo failures” can and will occur. The following information is c provided in order to help properly identify the true cause of a “turbocharger failure”. c The key to the proper diagnosis of turbo problems is to perform ALL the inspections rather than to stop when one condition is observed. In many cases, several symptoms c will be present, and all must be reviewed to fully understand what occurred. There are 4 external inspection areas: 6 c 2. Exhaust Outlet Inspection c c 3. Exhaust Inlet c Inspection - 1. Air Inlet & G Impeller Inspection G 4. External Gears G and Oil Drainage Screen Inspection G G c c c c Figure 7-28 External lnspection Areas G c - ITS LocomotiveTraining Series Student Text 7-33 I c  3 1. AIR INLET AND IMPELLER INSPECTION (Remove Air Inlet Boot to View) Inspect for the following conditions: a. Broken Impeller Blades: Indicate possible foreign object damage, or metal fatigue. b. Nicked Leading Edges on Impeller Blades: Indicates foreign object passage through air stream. Check air filter box, air duct, and replace air filters. C. Blade Rub on Inside of Cast Iron Impeller Cover: Indicates loss of support of turbine wheel in the form of a compressor, turbine, or thrust bearing failure. However, the cause of the bearing failure must also be determined. Continue with the inspections. NOTE: Always replace air filters and check aftercooler cores, aftercooler ducts, and air box for aluminum debris. d. Impeller Locks-Up When Rotated Clockwise: Turning the impeller by hand in a counter-clockwise direction should result in a freewheeling condition. When turned clockwise, the impeller should “lock-up”.If the impeller free-wheels in both directions, either the clutch has failed completely, or a planetary system failure has occurred. If the impeller cannot be turned in either direction, the rotor is locked-up, and the inspection should continue. 2. EXHAUST OUTLET INSPECTION: (View Down the Exhaust Duct of the Turbo) Inspect for the following conditions: a. Warped Exhaust Diffuser: Exhaust diffuser vanes will appear to be “wavy” when viewed from above if the turbo has been subjected to an “Overheat-Overspeed” condition. The thermal expansion which occurs at escalated temperatures causes the part to “grow”. The diffuser is secured in position within the turbo by a series of metal rods. If it becomes overheated, this expansion forces the thin metal vanes to distort permanently. A warped diffuser is always an indication of excessive engine exhaust gas temperatures. When a condition exists within an engine that results in excessive exhaust heat energy, the high heat level causes the turbine to spin faster than normal. Consequently, the name “Ov&eet-Wetspeed” is associated with this phenomenon. As the turbine spins faster, the blades begin to soften and stretch, and may eventually bred. Also, the impeller tries to pull the turbine wheel forward, out through the air inlet. This overloads the thrust bearing and usually causes it to fail as well. I7-34 Electrdvlotive Model 567.645 & 710 Series Diesel Engines 13 L ) i C c c e c Typical causes of excessive heat energy are: G 1. Broken Piston Rings e 2. Worn Injector Tips c 3. Broken Exhaust Valves c 4. Improperly Timed Fuel Injectors 5. Incorrect Valve Timing c 6. Plugged Aftercooler Cores c 7. Plugged Engine Air Filters c Any of these conditions can provoke either an “Air Box Fire” or an c “Exhaust Manifold Fire”. Evidence of such fires will be found in the form of gray colored ash at localized areas where the fire occurred. Thus, it is c necessary to inspect the air box and the exhaust manifold with a bright lamp whenever an Overheatloverspeed failure claims a turbo. Unless the condi- c tion is detected and corrected, it will continue to damage replacement turbos. c c Air boxes should be cleaned whenever a thick, wet, sponge-like soot deposit accumulates to depths approximating l/2”. The cause of the deposit c formation must be found and corrected. c b. Bulged or Punctured Turbine Shroud: The turbine wheel blades are c surrounded by a band or shroud. The clearance between this shroud and the blade tips is quite small. Consequently, in the event that an G Overheatloverspeed occurs, any plates which stretch will likely contact the shroud and deform or bulge it. In cases of blade breakage, the c shroud may become punctured. c C. Broken Shroud Retainer Clamp: A narrow clamping ring is used to G secure the shroud in most turbos. In some cases, this clamp may break due to metal fatigue. If this is observed, the turbo must be removed c immediately. If the shroud drops from its pilot, it will damage the turbine blades. c e d. Oil Out of the Exhaust Stack: The seals in the turbo require air to function properly. If the Engine Air Filters are restrictive, the turbo G seals may be starved for sufficient air. Check the filter pressuredrop prior to changing the turbo. Also, the source of the oil may be within C the engine itself. Before changing the turbo, remove the exhaust e screen and check the turbine inlet for wet, shiny deposits, which indicate the oil is coming from the engine, not the turbo. c c C c G c ITS Locomotive Training Series -StudentText 7-35 II 0  3 lc3 3. EXHAUST INLET INSPECTION: (Remove Inlet Screen to View) 3 a. Wet, Oily Deposits: The inlet should appear to be dry, with a light amount of ol) flat-black, sooty coloring. If wet, shiny deposits are observed, the engine prob bb ably has an oil control problem, and an exhaust manifold or air box fire may occur at any time. 3 b. Bent or Plugged Nozzle Ring Passages: Using a bright lamp, view into the 3 turbine exhaust inlet. The nozzle ring, which is a series of stationary vanes, will be observed. Exhaust gas must flow through this ring in order to act upon the 3 blades in the rotating assembly. If the nozzle is dented and bent, it is generally 3 an indication of foreign object passage. Also, deposits formed on the openings indicate an engine problem such as a cooling water leak. Deposits can also form 3 due to the type of fuel used. In any case, the restriction to gas flow imposed by dented or plugged nozzles can cause the turbo to surge or “burp” at higher u engine speeds. This is an undesirable condition. 3 C. Nicked or Broken Turbine Blades: The blades around the rim of the turbine 3 wheel cause the rotating assembly to spin whenever exhaust gas flows through them. If they are nicked, foreign material has passed through with the gas. This 3 material is generally in the form of small, sharp pieces of broken piston rings or exhaust valves. The nicked blades in the turbine wheel unbalance the high- 3 speed rotating assembly, and a compressor or turbine bearing failure will gener- 3 ally occur if the turbo is permitted to remain in operation. In some cases, the blades may break due to: a severe impact; stretching as a result of an overheat/ u overspeed; or metal fatigue. In such instances, the rotor unbalance is tremen- dous and a s