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78-662: The EMD AEM-7 is a twin-cab four-axle 7,000 hp (5.2 MW) B-B electric locomotive built by Electro-Motive Division (EMD) and ASEA between 1978 and 1988. The locomotive is a derivative of the Swedish SJ Rc4 designed for passenger service in the United States . The primary customer was Amtrak , which bought 54 for use on the Northeast Corridor and Keystone Corridor . Two commuter operators, MARC and SEPTA , also purchased locomotives, for

156-416: A constant of 0.85 but builders of industrial locomotives often used a lower figure, typically 0.75. The constant c also depends on the cylinder dimensions and the time at which the steam inlet valves are open; if the steam inlet valves are closed immediately after obtaining full cylinder pressure the piston force can be expected to have dropped to less than half the initial force. giving a low c value. If

234-783: A farewell excursion for the AEM-7 and ALP-44 locomotives along the Paoli/Thorndale Line . Two locomotives, ex-Amtrak Nos. 928 and 942, were moved to the Transportation Technology Center in July 2017. Caltrain , which operates commuter trains in the San Francisco Bay Area , purchased two retired Amtrak AEM-7s to test their electrification system once completed. The units would also serve as backup power for EMU cars. On June 7, 2018,

312-718: A hinge. Examples include the Milwaukee Road EF-1 "Boxcab" electrics. "B+B-B+B" means there are four trucks under the unit. Within each truck, there are two powered axles, and pairs of them are connected by span bolsters . One example would be the General Electric U50 , built from 1963 to 1965. The 4500 horsepower (3.4 MW) turbine locomotives built by GE for Union Pacific also used this arrangement. The EFVM railway of Brazil uses narrow gauge GE "BB" locomotives with this arrangement, both with "standard" and wide cabs. A GE Dash 9-40BBW , for instance,

390-440: A locomotive's mechanical characteristics (e.g., steam pressure, weight, etc.), or by actual testing with strain sensors on the drawbar and a dynamometer car . Power at rail is a railway term for the available power for traction, that is, the power that is available to propel the train. An estimate for the tractive effort of a single cylinder steam locomotive can be obtained from the cylinder pressure, cylinder bore, stroke of

468-410: A pair of high-powered B-B locomotives on a common frame as far as traction and power was concerned). In fact, a usual consist of a D-D unit included a leading C-C unit and a trailing C-C unit, for a total of about 12,600 hp (9.4 MW) (with four total prime-movers). With today's higher horsepower C-C units (about 4,300 hp (3.2 MW) apiece), three such C-C units exceeds the total power of

546-577: A plan to buy 30 locomotives for $ 77.8 million. Five groups bid on the contract: General Motors' Electro-Motive Division (EMD)/ ASEA , Morrison–Knudsen / Alstom , Brown Boveri , Siemens / KraussMaffei , and AEG / KraussMaffei . Amtrak awarded the contract to the EMD/ASEA partnership in January 1978. It ordered 17 more locomotives in February 1980, bringing the total to 47. The Railroad Test Track at

624-412: A rigid-framed locomotive. Later two-cylinder passenger locomotives were generally 40,000 to 80,000 lbf (170 to 350 kN) of T.E. For an electric locomotive or a diesel-electric locomotive , starting tractive effort can be calculated from the amount of weight on the driving wheels (which may be less than the total locomotive weight in some cases), combined stall torque of the traction motors ,

702-442: A row, "C" to three powered axles in a row, and "D" to four powered axles in a row. "1" refers to one idler axle, and "2" to two idler axles in a row. A dash ("–") separates trucks or wheel assemblies. A plus sign ("+") refers to articulation, either by connecting bogies with span bolsters or by connecting individual locomotives via solid drawbars instead of couplers . "1A-A1" means there are two trucks (or wheel assemblies) under

780-524: A special farewell excursion that ran between Washington, D.C., and Philadelphia. While Amtrak was replacing its AEM-7s, MARC initially decided in 2013 to phase out its electric operations on the Penn Line altogether and retire both its AEM-7 and Bombardier–Alstom HHP-8 locomotives, but the railroad instead started a refurbishment program for its HHP-8s in 2017. As of September 2017, the first HHP-8 reconditioned under this program had been delivered and

858-923: A total of 65. Amtrak ordered the AEM-7 after the failure of the GE E60 locomotive. The first locomotives entered service in 1980 and were an immediate success, ending a decade of uncertainty on the Northeast Corridor. In the late 1990s, Amtrak rebuilt 29 of its locomotives from DC to AC traction. The locomotives continued operating through the arrival of the final Siemens ACS-64 in June 2016. MARC retired its fleet in April 2017 in favor of Siemens Chargers , and SEPTA retired all seven of its AEM-7s in November 2018 in favor of ACS-64s. Amtrak assumed control of almost all private sector intercity passenger rail service in

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936-523: A two-cylinder locomotive): where The constant 0.85 was the Association of American Railroads (AAR) standard for such calculations, and overestimated the efficiency of some locomotives and underestimated that of others. Modern locomotives with roller bearings were probably underestimated. European designers used a constant of 0.6 instead of 0.85, so the two cannot be compared without a conversion factor. In Britain main-line railways generally used

1014-490: Is "Four axle". "B-2-B" means there are three trucks. The center truck has two unpowered axles and the truck at each end has two powered axles. The locomotive frame must either articulate or allow for significant side play to be provided to the center truck. Examples of this type were built as light rail vehicles. "B-B-B" means there are three trucks. Each truck has two powered axles. The locomotive frame must either articulate or allow for significant side play to be provided to

1092-408: Is "Six axle". "1-C+C-1" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with one idler axle, and inboard of it are three powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The PRR FF1 and FF2 electric locomotives used this arrangement. "2-C+C-2" means there are two sets of articulated axles under

1170-523: Is a guiding truck with two idler axles, and inboard of this, and hinged to it, is a truck with three powered axles. The GE steam turbine-electric locomotives of 1939 were notable examples of this arrangement. "2-C1+2-C1-B" means there are five trucks. Only the first three axles on the four-axle trucks were powered, as were both axles in the last truck; the first and middle trucks had two unpowered axles each. The only examples of this arrangement were three unique coal -fired steam-turbine locomotives built by

1248-584: Is a narrow-gauge adaptation of the SD45 , which required additional axles due to using smaller traction motors. "2-D+D-2" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. Examples include the Baldwin DR-12-8-1500/2 "Centipede" diesel locomotives and

1326-751: Is a truck with two idler axles, and inboard of it are four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The Little Joes , Baldwin DR-12-8-1500/2 , and Baldwin 4-8+8-4-750/8-DE locomotives used this arrangement. "D-D" means there are two trucks each with four powered axles. Examples include the EMD DD units. D-D locomotives have fallen out of favor as nearly all of these were twin-engined locomotives, which placed too much horsepower in too few axles which made these consists rather inflexible (each locomotive featured two prime movers , making each unit essentially

1404-399: Is a wide cab GE Dash 9-40CW series 4,000 hp (3,000 kW) locomotive with a B+B-B+B wheel arrangement. The EMD SD70ACe-BB produced from 2015 onward also has a B+B-B+B arrangement. "B-B+B-B" means that the locomotive has four trucks. Each truck contains two powered axles. The middle pair of trucks are connected by a span bolster . In most cases, the locomotive is articulated over

1482-427: Is inversely proportional to speed (constant power). Tractive effort curves often have graphs of rolling resistance superimposed on them—the intersection of the rolling resistance graph and tractive effort graph gives the maximum velocity at zero grade (when net tractive effort is zero). In order to start a train and accelerate it to a given speed, the locomotive(s) must develop sufficient tractive force to overcome

1560-434: Is often shown in graph form at a range of speeds as part of a tractive effort curve . Vehicles having a hydrodynamic coupling , hydrodynamic torque multiplier or electric motor as part of the power transmission system may also have a maximum continuous tractive effort rating, which is the highest tractive force that can be produced for a short period of time without causing component harm. The period of time for which

1638-551: Is under the back of the unit, and has one idler axle. Examples include the three EMD LWT12 locomotives built by EMD in 1956. Twenty SD70ACe-P4 locomotives were built by EMD with a B1-1B arrangement that has two three axle trucks with each truck having two AC traction motors and one idler axle nearest the fuel tank. The locomotive was designed as an AC traction alternative to the SD70M-2 that uses three DC traction motors on each of two three axle trucks. Only BNSF ordered

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1716-465: Is under the back of the unit, and has two idler axles in a row. Examples include the three lightweight RP-210 locomotives built by Baldwin in 1956 and 1957 for use with Pullman-Standard Train-X equipment. "B-A1A" means there are two trucks. The "B" truck is under the front of the unit, and has two powered axles. The "A1A" truck is under the back of the unit, and has one powered axle, one idler axle, and one more powered axle. Examples include some of

1794-600: Is under the front of the unit, and has one powered axle, one idler axle, and one more powered axle. The "3" truck is under the back of the unit, and has three idler axles in a row. An example is the Baldwin DR-6-2-10 1,000 hp (750 kW) cab unit, only one of which was built for the Chicago and North Western Railway in 1948. "A1A-A1A" means there are two trucks under the locomotive. Each truck has two powered axles, with an idler axle between them. This spreads

1872-539: Is under the front of the unit, and has three idler axles in a row. The "A1A" truck is under the rear of the unit, and has one powered axle, one idler axle, and one more powered axle. An example is the later built FM OP800 800 hp (600 kW) railcar, six of which were built by the St. Louis Car Company exclusively for the Southern Railway in 1939. "A1-1A" means there are two trucks or wheel assemblies under

1950-758: The Baldwin Locomotive Works for the Chesapeake and Ohio Railway between 1947 and 1948. This locomotive is sometimes called the M-1. "C-C+C-C" means there are four trucks under the unit. Each truck has three powered axles. The only examples of this type were the 8500 horsepower (6.3 MW) turbine locomotives built by General Electric for Union Pacific . These locomotives consisted of two permanently coupled C-C units. "C+C-C+C" means there are four trucks. Each truck has three powered axles and pairs of them are connected by span bolsters . This arrangement

2028-834: The British Rail Class 28 are the only locomotives to use this wheel arrangement. "C-C" means there are two identical trucks. Each truck has three powered axles. Examples include the EMD SD (Special Duty), GMD GF6C , EMD GM6C , PRR E44 , GE E60 , Virginian EL-C and GE Evolution Series units, except the ES44C4 and ET44C4 which use the A1A-A1A wheel arrangement. This is a currently popular configuration used in low-speed, high-weight applications, such as unit coal trains. General ("manifest") freight trains also use C-C locomotives. See also Co-Co . An American colloquialism of "C-C"

2106-576: The Budd Metroliner electric multiple units and PRR GG1 locomotives. The latter were over 35 years old and restricted to 85 mph (137 km/h). Amtrak sought a replacement, but no US manufacturer offered an electric passenger locomotive. Importing and adapting a European locomotive would require a three-year lead time. With few other options, Amtrak turned to GE to adapt the E60C freight locomotive for passenger service. GE delivered two models,

2184-931: The FM C-liners (most passenger units) built from 1950 to 1955, and the EMD FL9 . "B-B" means there are two identical trucks. Each truck has two powered axles, a currently popular configuration used in high-speed, low-weight applications such as intermodal trains and high-speed rail , as well as switcher locomotives . Examples include the EMD GP (General Purpose), EMD F-units , EMD SW1500 , Acela Express Power Cars , Siemens Charger , Siemens ACS-64 and GE Genesis units. High speed ("time") freight trains, with guaranteed schedules often use B-B locomotives of 3,800 HP (950 HP per axle), but this application, too, has largely been replaced by higher-powered, 4,500 HP C-C locomotives (750 HP per axle). An American colloquialism of "B-B"

2262-621: The GE " Little Joe " electric locomotives . "B-D+D-B" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two powered axles, and inboard of it are four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The W-1 class of electric locomotives built by General Electric for the Great Northern Railway used this arrangement. "1B+D+D+B1" means there are four sets of articulated axles under

2340-532: The GE E60s were sold to other operators. The new locomotives swiftly proved themselves; Car and Locomotive Cyclopedia stated that no new locomotive since the New York Central Hudson had "such an impact on speeds and schedule performance." This strong performance led to further orders. Amtrak added seven more locomotives in 1987, delivered in 1988, for a total of 54. Two commuter operators in

2418-535: The Great Northern Z-1 electric locomotives (for the Cascade Tunnel electrification) used this arrangement. "2-D-2" means there are three trucks. At either end are trucks with two idler axles; the center truck has four powered axles. The PRR R1 electric locomotive used this arrangement. "2-D+D-2" means there are two sets of articulated axles under the unit. Within each of these sets, theare

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2496-795: The Railroad Museum of Pennsylvania , 945 at the Illinois Railway Museum , and 917 at the Danbury Railway Museum . For 150 mph (241 km/h) or more in the US, see High-speed rail in the United States AAR wheel arrangement#B-B The AAR system (like UIC) counts axles, unlike Whyte, which counts wheels. Letters refer to powered axles, and numbers to unpowered (or idler) axles. "A" refers to one powered axle, "B" to two powered axles in

2574-492: The Southern Railway in 1939. "2-B" means there are two trucks or wheel assemblies. The "2" truck is under the front of the unit, and has two idler axles in a row. The "B" truck is under the rear of the unit, and has two powered axles. Examples include the three lightweight power cars built by ALCO / ACF in 1935 and 1937 for use with the Rebel streamliners. "3-A1A" means there are two trucks or wheel assemblies. The "3" truck

2652-546: The Texas Mexican Railway . "2-A1A" means there are two trucks or wheel assemblies. The "2" truck is under the front of the unit, and has two idler axles in a row. The "A1A" truck is under the rear of the unit, and has one powered axle, one idler axle, and one more powered axle. An example is the FM OP800 800 hp (600 kW) railcar, six of which were built by the St. Louis Car Company exclusively for

2730-610: The Transportation Test Center in Pueblo, Colorado was electrified in 1979 under sponsorship by the Northeast Corridor. The first locomotive completed, No. 900, was delivered to Amtrak in February 1980, then after acceptance testing, it was shipped to TTC for performance tests from April 1980 to May 1981. Testing included evaluation of three different pantograph designs, instantaneous power and total energy consumed during operation, and reliability testing, during which

2808-492: The Virginian Railway 's EL-2B electric locomotives. Tractive effort In railway engineering, the term tractive effort describes the pulling or pushing capability of a locomotive . The published tractive force value for any vehicle may be theoretical—that is, calculated from known or implied mechanical properties—or obtained via testing under controlled conditions. The discussion herein covers

2886-496: The gear ratio between the traction motors and axles, and driving wheel diameter . For a diesel-hydraulic locomotive , the starting tractive effort is affected by the stall torque of the torque converter , as well as gearing, wheel diameter and locomotive weight. The relationship between power and tractive effort was expressed by Hay (1978) as where Freight locomotives are designed to produce higher maximum tractive effort than passenger units of equivalent power, necessitated by

2964-459: The "1" truck is under the front of the unit, and has one idler axle. The remaining 4 axles are rigidly mounted to the frame behind this lead truck (or grouped in a second truck). This is roughly the equivalent of a 2-8-0 Consolidation in the Whyte notation, particularly when built as a 1-truck/4 rigid axle locomotive. The only known examples are a series of diesel boxcab locomotives built and owned by

3042-455: The AEM-7 was operated for 156,200 mi (251,400 km). Revenue service began on May 9, 1980, when No. 901 departed Washington Union Station with a Metroliner service. The Swedish influence led to the nickname "Meatball", after Swedish meatballs . Railfans nicknamed the boxy locomotives "toasters". Between 1980 and 1982, 47 AEM-7s (Nos. 900–946) went into service. Amtrak retired the last of its PRR GG1s on May 1, 1981, while most of

3120-601: The E60CP and the E60CH. However, the locomotives proved unsuitable for speeds above 90 mph (145 km/h), leaving Amtrak once again in need of a permanent solution. Amtrak then examined existing European high-speed designs, and two were imported for trials in 1976–77: the Swedish SJ Rc4 (Amtrak No. X995, SJ No. 1166), and the French SNCF Class CC 21000 (Amtrak No. X996, SNCF No. 21003). Amtrak favored

3198-787: The E60CP or the GG1. On its introduction it was the "smallest and lightest high horsepower locomotive in North America." The Budd Company manufactured the carbodies for the initial Amtrak order, while the Austrian firm Simmering-Graz-Pauker built the carbodies for the MARC and SEPTA orders. Reflecting the varied electrification schemes on the Northeast Corridor the locomotives could operate at three different voltages: 11 kV 25 Hz AC , 12.5 kV 60 Hz AC and 25 kV 60 Hz . A pair of Faiveley DS-11 two-stage pantographs , one at each end of

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3276-642: The HEP capacity of the original DC units. The 6 FXA 5856 traction motors, from Alstom's ONIX family of propulsion components, had a maximum rating of 1,250–1,275 kilowatts (1,676–1,710 horsepower) each and a continuous rating of 1,080 kilowatts (1,450 horsepower). The remanufactured AEM-7ACs were the world's first passenger locomotives to incorporate IGBT technology. Amtrak planned a fleet of 53 locomotives, with an estimated cost of $ 137.5 million. Limited funding hampered that plan, but in September 1977 Amtrak proceeded with

3354-399: The Northeast Corridor, reached the end of their service lives. In 1999, Amtrak and Alstom began a remanufacturing program for Amtrak's AEM-7s. Alstom supplied AC propulsion equipment, electrical cabinets, transformers, HEP, and cab displays. The rebuild provided Amtrak with locomotives that had improved high end tractive effort and performance with longer trains. Amtrak workers performed

3432-743: The Northeast ordered AEM-7s. MARC ordered four in 1986 for use on its Penn Line service on the Northeast Corridor between Washington, D.C. , and Perryville, Maryland . The Southeastern Pennsylvania Transportation Authority (SEPTA) ordered seven in 1987. Amtrak also used the AEM-7s to handle the Keystone Service on the Keystone Corridor between Harrisburg and Philadelphia as the Budd Metroliners, displaced from

3510-512: The Swedish design, which became the basis for the AEM-7. The AEM-7 was far smaller than its predecessors, the PRR GG1 and the GE E60 . It measured 51 ft 1 + 25 ⁄ 32  in (15.59 m) long by 10 ft 2 in (3.10 m) wide, and stood 14 ft 9.5 in (4.51 m) tall, a decrease in length of over 20 ft (6.1 m). The AEM-7's weight was half that of

3588-505: The UK, the Class 31 uses this wheel arrangement. "A1A-B+B" means there are three trucks. The first truck has three axles, with the center one unpowered. A pair of two-axle trucks, each with both axles powered, are connected by a span bolster under the rear of the unit. The only example to date of this arrangement was a single experimental EMD SDP45 . "B" means there are two powered axles under

3666-473: The United States on May 1, 1971, with a mandate to reverse decades of decline. Amtrak retained approximately 184 of the 440 trains which had run the day before. To operate these trains, Amtrak inherited a fleet of 300 locomotives ( electric and diesel ) and 1190 passenger cars , most of which dated from the 1940s–1950s. Operation on the electrified portion of the Northeast Corridor was split between

3744-522: The board awarded two contracts totalling approximately $ 600,000: one to purchase two AEM-7ACs from Mitsui & Co, and the other to Amtrak for refurbishment, training, and transportation to the Caltrain maintenance facility in San Jose . Locomotive Nos. 929 and 938 were delivered to California by Amtrak in June 2019. The seven SEPTA AEM-7s were leased to NJ Transit beginning in late December 2018 for

3822-505: The center truck. The Russian VL85 and US-American EMD GM10B was a notable example. See also Bo-Bo-Bo . "B+B+B" means there are three articulated sets of two powered axles each under the unit. The locomotive frame must allow for significant side play to be provided to the center axle set, as well as allowing for end play for the end sets. The ten Mexican Railway GE boxcab electrics of 1923 are examples of this wheel arrangement. "2-B+B-2" means there are two sets of articulated axles under

3900-438: The center trucks. "B-B+B-B+B-B" means that the locomotive has six trucks. Each truck contains two powered axles. The only known locomotives to have this configuration were the two EMD TR3 locomotives made of three permanently coupled B-B units, which had solid drawbars connecting the units instead of the typical couplers. "C" means there are three powered axles under the unit. They are not articulated relative to other parts of

3978-841: The cylinder valves are left open for longer the value of c will rise nearer to one. The result should be multiplied by 1.5 for a three-cylinder locomotive and by two for a four-cylinder locomotive. Alternatively, tractive effort of all "simple" (i.e. non-compound) locomotives can be calculated thus: { t } l b f = 0.85 { d } i n 2 n { s } i n { p } p s i 2 { w } i n , {\displaystyle \{t\}_{\mathrm {lbf} }={\frac {0.85\{d\}_{\mathrm {in} }^{2}n\{s\}_{\mathrm {in} }\{p\}_{\mathrm {psi} }}{2\{w\}_{\mathrm {in} }}},} where For other numbers and combinations of cylinders, including double and triple expansion engines

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4056-456: The driving wheels, the wheel diameter, coefficient of friction ( μ ) between the driving wheels and supporting surface, and the weight applied to the driving wheels ( mg ). The product of μ and mg is the factor of adhesion , which determines the maximum torque that can be applied before the onset of wheelspin or wheelslip . Tractive effort inversely varies with speed at any given level of available power. Continuous tractive effort

4134-418: The locomotive, collected power from the overhead catenary wire. Thyristor converters stepped down the high-voltage AC to provide DC power at a much lower voltage to four traction motors, one per axle. As built the AEM-7 was rated at 7,000 hp (5.2 MW), with a starting tractive effort of 51,710 lbf (230 kN) and a continuous tractive effort of 28,100 lbf (125 kN). Its maximum speed

4212-509: The locomotive. This arrangement is only used on very small locomotives (e.g. the PRR B1 ). This arrangement is sometimes referred to as 0-6-0 , the Whyte notation equivalent. "C-B" means there are two trucks. The "C" truck is under the front of the unit, and has three powered axles. The "B" truck is under the rear of the unit, and has two powered axles. The Japanese DE10 , DE11 , and DE15 and

4290-447: The maximum continuous tractive effort may be safely generated is usually limited by thermal considerations. such as temperature rise in a traction motor . Specifications of locomotives often include tractive effort curves, showing the relationship between tractive effort and velocity. The shape of the graph is shown at right. The line AB shows operation at the maximum tractive effort, the line BC shows continuous tractive effort that

4368-477: The model in 2014. The other locomotive with this wheel arrangement is the EMD SD70MACH , which is an SD70MAC rebuilt by Progress Rail for Metra and used for passenger service. In 2020, Metra approved of the purchase of 15 of these locomotives with options to purchase up to 27 more. "B-2" means there are two trucks. The "B" truck is under the front of the unit, and has two powered axles. The "2" truck

4446-661: The much higher weight that is typical of a freight train. In modern locomotives, the gearing between the traction motors and axles is selected to suit the type of service in which the unit will be operated. As traction motors have a maximum speed at which they can rotate without incurring damage, gearing for higher tractive effort is at the expense of top speed. Conversely, the gearing used with passenger locomotives favors speed over maximum tractive effort. Electric locomotives with monomotor bogies are sometimes fitted with two-speed gearing. This allows higher tractive effort for hauling freight trains but at reduced speed. Examples include

4524-640: The overhauls under Alstom supervision at Amtrak's shop in Wilmington, Delaware . These remanufactured AEM-7s were designated AEM-7AC . Between 1999 and 2002, Amtrak rebuilt 29 of its AEM-7s. As the locomotives passed 30 years of service their operators made plans for replacements. In 2010, Amtrak ordered 70 Siemens ACS-64 locomotives to replace both the AEM-7s and the newer but unreliable Bombardier/Alstom HHP-8s . The ACS-64s began entering revenue service in February 2014. The last two active AEM-7s, Amtrak Nos. 942 and 946, made their final run on June 18, 2016, on

4602-404: The piston and the diameter of the wheel. The torque developed by the linear motion of the piston depends on the angle that the driving rod makes with the tangent of the radius on the driving wheel. For a more useful value an average value over the rotation of the wheel is used. The driving force is the torque divided by the wheel radius. As an approximation, the following formula can be used (for

4680-464: The purpose of allowing NJ Transit to roster additional locomotives equipped with positive train control (PTC) in order to meet a deadline for operating PTC-capable equipment. However, they were never used and subsequently returned. SEPTA then used them exclusively for overnight work service during autumn, cleaning tracks and applying traction gel . In 2022, SEPTA sold the AEM-7s and ALP-44 for scrap. Three ex-Amtrak units have been preserved: Nos. 915 at

4758-466: The rolling friction between wheels and rails. If acceleration continues, the train will eventually attain a speed at which the available tractive force of the locomotive(s) will exactly offset the total drag, causing acceleration to cease. This top speed will be increased on a downgrade due to gravity assisting the motive power, and will be decreased on an upgrade due to gravity opposing the motive power. Tractive effort can be theoretically calculated from

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4836-509: The span bolster. The Union Pacific 's M-10002 diesel streamliner and New York Central 's T-Motor third-rail electric locomotives are examples of this type. This arrangement also includes locomotives made of two permanently coupled B-B units, such as some EMD FT units which had a solid drawbar connecting two units instead of the typical couplers. "B-B-B-B" means there are four trucks. Each truck has two powered axles. The locomotive frame must allow for significant side play to be provided to

4914-431: The term's usage in mechanical applications in which the final stage of the power transmission system is one or more wheels in frictional contact with a railroad track . The term tractive effort is often qualified as starting tractive effort , continuous tractive effort and maximum tractive effort . These terms apply to different operating conditions, but are related by common mechanical factors: input torque to

4992-401: The tractive effort can be estimated by adding the tractive efforts due to the individual cylinders at their respective pressures and cylinder strokes. Tractive effort is the figure often quoted when comparing the powers of steam locomotives, but is misleading because tractive effort shows the ability to start a train, not the ability to haul it. Possibly the highest tractive effort ever claimed

5070-468: The train's resistance , which is a combination of axle bearing friction, the friction of the wheels on the rails (which is substantially greater on curved track than on tangent track), and the force of gravity if on a grade . Once in motion, the train will develop additional drag as it accelerates due to aerodynamic forces , which increase with the square of the speed. Drag may also be produced at speed due to truck (bogie) hunting , which will increase

5148-462: The unit. At each end, there is one unpowered axle and two powered axles, hinged to a set of four powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The "Bi-Polar" electric locomotives used by the Milwaukee Road used this arrangement. "(B+B-B+B)+(B+B-B+B)" means there are 2 units, each with 4 trucks in a B+B-B+B wheel arrangement. An example was

5226-595: The unit. Each truck has one powered axle and one idler axle, with the idler axles to the outside. Examples include Budd RDC diesel multiple unit ( DMU ) cars. "1B-1B" means there are two trucks with a leading idler axle in front of two powered axles. This arrangement was used to upgrade the B-B arrangement of two EMC 1800 hp B-B locomotives owned by the Santa Fe Railroad in 1938, for greater stability at speed. "1-D" means there are two trucks or groups of axles;

5304-608: The unit. Each truck has one powered axle and one idler axle, with the powered axles to the outside. "A1A-2" means there are two trucks. The "A1A" truck is under the front of the unit, and has one powered axle, one idler axle, and one more powered axle. The "2" truck is under the back of the unit, and has two idler axles in a row. An example is the Silver Charger power car for the General Pershing Zephyr . "A1A-3" means there are two trucks. The "A1A" truck

5382-466: The unit. These axles are not articulated relative to other parts of the locomotive. This arrangement is only used on very small locomotives, such as the EMD Model 40 . It is also used on speeders . This arrangement is sometimes referred to as 0-4-0 , the Whyte notation equivalent. "B-1" means there are two trucks. The "B" truck is under the front of the unit, and has two powered axles. The "1" truck

5460-420: The unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are three powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The Pennsylvania Railroad 's GG1 and Companhia Paulista 's electric locomotives were notable examples of this arrangement. "2+C-C+2" means there are two sets of axles under the unit. Within each of these sets, there

5538-570: The unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are two powered axles. Two of these articulated sets are placed back to back and connected by a hinge. The PRR DD1 and DD2 electric locomotives used this arrangement. "2-B+B+B+B-2" means there are two sets of articulated axles under the unit. Within each of these sets, there is a truck with two idler axles, and inboard of it are two powered axles, hinged to yet another set of two powered axles. Two of these articulated sets are placed back to back and connected by

5616-499: The usual D-D consist by 300 hp (220 kW) (with one fewer prime-mover than a usual D-D consist, thereby significantly improving reliability and dramatically reducing maintenance). Although the D-D arrangement is associated with twin-prime-mover locomotives of high power, this does not mean a D-D with a single high-power prime mover may be built in the future, nor does it exclude two-truck, eight-axle electric locomotive. The EMD DDM45

5694-594: The usual formula). The Union Pacific Big Boys had a starting T.E. of 135,375 lbf (602 kN); the Norfolk & Western 's Y5, Y6, Y6a, and Y6b class 2-8-8-2s had a starting T.E. of 152,206 lbf (677 kN) in simple expansion mode (later modified to 170,000 lbf (756 kN), claim some enthusiasts); and the Pennsylvania Railroad 's freight duplex Q2 attained 114,860 lbf (510.9 kN, including booster)—the highest for

5772-540: The weight of the locomotive more evenly over the track and counteracts the tendency of trucks to oscillate at high speeds, which is a problem with two axle trucks. The idler wheels may be smaller than the powered wheels. Examples of locomotives with this wheel arrangement include the EMD E-units and ALCO PAs , which were high speed passenger locomotives, and the dual service FM Erie-built . BNSF took delivery of ES44C4 locomotives with this type of truck in 2009. In

5850-522: Was 125 miles per hour (201.2 km/h). A separate static converter supplied 500 kW 480 V head-end power (HEP) for passenger comfort. This was sufficient to supply heating, lighting, and other electrical needs in 8-10 Amfleet cars. The rebuilt AEM-7ACs used AC traction instead of DC traction. The power modules used water-cooled insulated-gate bipolar transistor (IGBT) technology and provided about 5,000 kilowatts (6,700 horsepower) of traction power plus 1,000 kilowatts (1,300 horsepower) of HEP, twice

5928-586: Was for the Virginian Railway 's 2-8-8-8-4 triplex locomotive, which in simple expansion mode had a calculated starting T.E. of 199,560 lbf (887.7 kN)—but the boiler could not produce enough steam to haul at speeds over 5 mph (8 km/h). Of more successful steam locomotives, those with the highest rated starting tractive effort were the Virginian Railway AE-class 2-10-10-2s , at 176,000 lbf (783 kN) in simple-expansion mode (or 162,200 lb if calculated by

6006-664: Was undergoing successful testing. MARC selected the Siemens Charger diesel locomotive as the replacement for its AEM-7 fleet in 2015. The last of the MARC AEM-7s were retired by April 2017, with the Chargers entering service in January 2018. SEPTA continues to use electric traction, replacing its seven AEM-7s and lone ABB ALP-44 , an improved AEM-7, with fifteen ACS-64s. The first SEPTA ACS-64, #901, entered revenue service on July 11, 2018. On December 1, 2018, SEPTA held

6084-625: Was used on the Jawn Henry coal -fired steam-turbine locomotive built by the Baldwin Locomotive Works for the Norfolk & Western Railway in May, 1954. "1-D-1" means there are three trucks under the unit. At either end are trucks with one idler axle; the center truck has four powered axles. The original 1904–1909 New York Central S-Motor third-rail electric locomotives (for the Grand Central Terminal electrification) and

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