An Electric Transmission for Armored Vehicles: A Designer’s Dream Realized at Last

The design of an armored fighting vehicle can only be a three-way trade-off between firepower, protection, and mobility. A tank that gives its crew good protection is necessarily heavily armored. This cuts down its tactical mobility, making it an easier target. On the other hand, a heavy and powerful armament adds weight to the vehicle, trading off mobility and weight available for armor protection. This leads to a vicious circle in armor design. Heavy weights and big volumes also make transportation over long distances very difficult. In the case of an armored personnel carrier, the problem is all the more complex because this type of vehicle needs not only space for its crew but also maximum room for a maximum number of passengers in acceptable comfort. On the other hand, to minimize its vulnerability it needs as low a silhouette as possible. These opposing requirements, Below, the power transmission layout of the WWI-era Daimler Petrol Electric tank drive. compactness and usable space, Below, the layout of the Britisl present the military engineers with Westinghouse Petrol Electric choices leading to a compromise. tank propulsion system. Because men are not compres-sable and need enough room to live and fight within the vehicle, the obvious solution is to reduce the dead weight and volume resulting from unnecessary mechanical components. Electrical transmission of power to the drive sprockets offers an interesting alternative to overcome the many design constraints that mechanical transmissions impose. The mechanical transmission of the common tracked armored vehicle is composed of an automatic or semi-automatic gearbox, differen-tials or torque converters, shafts, universal joints, final drives and track drive sprockcts. This setup imposes multiple design problems in weight and volume, as well as a mechanical complexity vulnerable to breakdowns. By contrast, electrical trans- m i s s i o n s eliminate the major part of weight and v o l u m e problems, resulting in overall design ad- v a n t a g e s. Electric current from a generator, rather than mechanical torque, moves through a cable to electric motors locatcd at each drive sprocket, at a considerable saving in weight and volume. This permits improvements in the general appearance and compactness of the vehicle. Reversing the prescnt circle in armor design permits the following advantages: 0 Less volume to protect reduces the weight of armor necessary to achieve a given ballistic protection. 0 Reduced weight results in a lower ground pressure, which improves the mobility of the vehicle on soft terrain. 0 A lighter vehicle pcrmits a suspension with external coil springs. This is lighter, cheaper, and easier to maintain than a torsion bar suspension, and it uses lighter tracks. These multiple reductions in weight require less automotive power, allowing the choice of a smaller, lighter, and more economical engine. A smaller engine has a lower fuel requirement. The resulting tanks 34 ARMOR - I are lighter and smaller for a given range of action. Further advantages of an electric drive system are: high mobility, full automatic system, ease of driving, and modular conception. The latter makes it possible to place the thermal motor in front of the vehicle, and the electric motors at the rear, or vice versa, which allows not only good weight distribution, but also the use of identical drive components for different types of vehicles of the same family. Not a New Idea The idea of giving tanks electric transmissions is practically as old as tanks themselves. In 1917, the French company Forges et Acieries de la Marine et d'Homecourt (FAMH), built 400 Sairir Cliariiorid tanks (23 tons) fitted with a Crochat-Collardeau "petroleo-electrique" electric transmission. The tank's Panhard engine coupled directly to an adjacent compound dynamo. This dynamo supplied current to two electric motors, each one mounted over a drive sprocket and driving a track. A foot pedal, which operated the main rheostat for the two driving motors, controlled speed and also controlled the gasoline engine carburetor. A secondary rheostat also controlled each electric motor, thereby providing steering. A pole charger permitted reversing the current flow to reverse the driving motor. Also in 1917, a tank went through trials in Great Britain with Daimler and British Westinghouse electric transmissions. The first one was on "Motlwr," an early design model; the second was renamed Dairitler Petrol Electric niacliine and used an upgraded (125 hp) Daimler engine with a dynamo directly coupled to it. Current went to two electric motors in series, each of which could be independently controlled by shifting the brushes. Each motor connected through a two-speed gearbox to a worm reduction gear, from which the drive passed through a further gear reduction to the sprockets driving the road chain driving wheels. By connecting the two w o r m - w h e e l shafts with a dog clutch, they obtained a differen-The TOG, a WWII-era British tank design, used an rial lock. electrical power transmission system, but was never produced for combat use. At first, this transmission seemed so promising that the Tank Supply Committee ordered 600 sets. On tests, however, the tractive effort was too low and could not pull the tank out of a shell hole. After much controversy and testing, the committee dismissed the Daimler Petrol Electric transmission and cancelled all orders. Commonly used on British trolleys, the British Westinghouse electric transmission, renamed British Westinghouse Petrol Electric machinc, went into a Murk IV tank with a beefed-up (115 hp) Daimler engine. This engine, moved towards the rear of the tank, allowed room for two generators in tandem in front of it, with one exciter between them. There was one electric motor on each side of the tank behind the engine, each driven by one of the generators. These motors drove the track through double-reduction spur gears, chain, sprocket-pinion and sprocket wheel. Control was by a rheostat on the exciter circuit of each motor, and special reversing switches were so inter-locked that they could not be operated before the current was switched off. Considered as satisfactory in some ways, the British Westinghouse petrol-electric transmission was too heavy, noisy, and cumbersome for practical purposes. In 1918, thc United States carried out trials with the experimental Holt Gas-Electric Tank, built through the collahoration of the Holt Manufacturing Co. and General Electric Co. A high-speed Holt engine operated a <;E generator, which provided the current to drive two electric motors, one for each track. Varying the current to the track-driving electric motors steered the tank; a brake on ARMOR - 35 each motor shaft held the track on the side toward the turn. With this transmission, the Holt tank weighed more than 20 metric tons, prohibitive for its size. In France, Peugeot built a "petroleo-electrique" tank prototype in 1918, and, between 1919 and 1921, the Societe des Forges et Chantiers de la Mediterranee (FCM) at La Seyne, near Toulon, produced ten 70-ton tanks, type 2C, with a more advanced system of electric transmission. The Sautter-Hade and Alsthom electric transmission for the 2C tank was ingenious hut very heavy. It had duplicate electric generators to compensate for any possible power failure. Two six-cylinder petrol engines drove two direct current generators through an "elastique" connection. If one of the tank's engines failed, the crew could connect both tracks to the remaining working engine. Each of the electric driving motors received a 300-volt current, which enabled the tank to continue to move and maneuver in spite of the much reduced power and speed. A small auxiliary motor drove a generator that served the main generators which, in turn, acted as starters for the two petrol engines. The electric transmission for the 2C tank weighed 16 tons, which was about 23 percent of the tank's weight. After a 15-year eclipse, the French Societe d'Etudes et d'Applications Mecaniques (SEAM) resurrected the idea with the Poriiatowski experimental tank constructed in 19%. In 1917, a "char de forteresse" programme - a tank capable of crossing Hindenburg Line obstacles and assaulting its blockhouses - led to the manufacture of a Full size mock-up of an FCM F1 tank, with an Alsthom electric transmission. Armed with along 105-mm gun and 75-mm guns in two turrets, it would have weighed 145 tons. WWII brought to a halt other projects for tanks with electric transmissions, including an assault tank by ARL. Wll Experiments But WW I1 re-launched studies in this field outside of France. In Great Britain, the British Electric Co. provided the electric transmission for the 654011 TOG, built by William Foster and Co. in

1940. The diesel engine drove two main generators, coupled mechanically. which, in turn. powered an electric motor for each track. The vehicle speed was controlled by a foot accelerator pedal, which operated the diesel engine throttle, controlling the vehicle's speed. A hand lever controlling the motor and generator field strengths provided a further variation in the vehicle's speed. A steering wheel operated a potentiometer rheostat, which varied the relative field strengths of the two generators. To turn the steering wheel either way caused the opposite motor to receive increascd voltage and power. The remaining motor sent power through its own generator to the outside track and assisted in the turn. It was also possible to reverse either motor independently and make a pivot turn. Air brakes could hold either track stationary for a skid turn. In Germany, Ferdinand Porsche designed the electric-driven VK-arid VK-4504fP) projects. In 1943, his company built 90 "EIejarit" (formerly 'Ferdinand") 65-ton tank destroyers, which had an electric transmission from Siemens-Schuck-ert of Berlin. Two parallel 300-hp Maybach engines drove a single gen- erator, which supplied current to two electric motors. These were located in a separate transmission compartment and were linked to their respective rear-drive sprockets through;L geared drive. Electrically operated, these gearboxes had a three-speed ratio available, forward or reverse, and a top speed rated at 20 k d h. A hydropneumatic assisted electric steering system had a final drive reduction ratio of 16.51. After December 1943, the Germans tested the prototype of a 180- ton monster tank, named "Maris". It was also equipped with a huge Siemens-Schuckert electric transmission. which included a tandem generator weighing 3.885 kg (8,547 Ibs) and two electric motors weighing 3,770 kg (8,294 Ibs), which drove simple reduction gears that could adjust to either road or crosscountry operation and gave Porsche's mobile pillbox a maximum speed of 20 kmk. An airstream from the engine fan cooled generators, electric motors, reduction gears, and brakes. Because there were few bridges capable of taking such a weight, the "Maris" had been designed to be submersible to an eight-meter depth. An attachable, single, big chimney served as air supply and emergency exit for the crew, as well as h cooling the electric motors. When a "Maris" had to cross a deep river, a cable from a second tank on the bank provided power. Once across, the first "Marrs" would power the second one through the same cable. The United States also had explored these ideas with a series of experimental tanks: the TIE1 heavy and the T23, 72.3E.3, T25, and T26 mediums. They had a GE electric transmission. The 250 tanks produced never saw combat. 36 ARMOR -

In 1?44, the Soviet army carried out trials with a prototype (IS-E) of the Staiiti heavy tank, with an electric transmission and a modified running gear. Up to this time, electric transmissions proved to be considerably heavier - three tons in the case of the British TOG - than an equivalent mechanical drive, although easier to control and readily applicable to the steering of the tracked vehicles. In the mid-l?60s, the FMC Corporation conducted experiments with a A4113 APC with both AC and DC types of electric drive. Ten years ago, a Belgian electrical and engineering company, the Ateliers de Constructions Electri-ques de Charleroi (ACEC). undertook the design and development of an electric transmission system for tracked armored vehicles. The company drew on its experience in the field of electric transmissions for locomotives and tramways. Its preliminary cxpericnces of an electric drive on an M24 Ciiuffee light tank, and then on an AMX-IOP APC, convinced the engineers that only an entirely new design would fully realize the potential of the electric transmission. This was the starting point for the design of the COBRA MlCV on which studies began in 1976. A first prototype (Pl) in mild-steel appeared in May 1978, fifteen months after its start on the drawing board. Two other Cobra prototypes (P2 and P3) appeared in armor plate in 1980, with various technical improvements (tracks, air conditioning, final drive). The Belean Army’s Military Board supervised trials of the Cobra (P3) at the Belgian Army’s Proving Ground at Brasschaat. The Cobra (P3) trials resulted anew prototype (P4) at the end of 1983. In Septem-her 1984, technicians from the U. S. Army’s Tank and Automotive Command (TACOM), visited ACEC and examined and tested the vehicle. From mid-1984 to May 1985, the Cobra (P4) underwent official trials at Brasschaat and at the maneuver terrain at Marche-en-Famenne. In October 1985, a pre-production vehicle, the COBRA-41 Mechanized Infantry Vehicle, left the ACEC factory in Ghent. It was followed in August 1986, by a Fire Support Vehicle, the COBRA-YO light tank, armed with a 90-mni gun. ACEC Electrical Transmission The ACEC electric transmission system for its Cobra vehicles is very light and efficient and consists of an At 188 tons, the huge German Maus heavy tank used electric drive but never got beyond the testing phase. The Maus being tested in photo has a large weight in place of the turret seen in plans at right. I ARMOR - 37

,- The Cobra 90 light tank, above, and the Cobra 41 APC, at right, are both powered by electric drives, but the powered sprockets are at the rear on the APC and at the front on the Cobra 90. The two vehicles illustrate the flexibility of layout possible with electrical drive. A diesel engine drives the electrical generators in both vehicles. alternator, a rectifier and two electric sprocket motors. The alternator is of the flywheel type, without endshields. The rotor is of the salient-pole type with annular field winding. It replaces the original flywheel and carries the starter ring. This construction does away with endshields and couplings. It is very simple, reliable and light. The rectifier is integrated into the alternator stator and is composed of a double silicon diode bridge (six components), and is cooled by the alternator’s fan. This diesel-electric power group occupies the same space as a normal diesel engine. The sprocket motors include a two-stage road and cross-country planetary reduction gear, which integrates a hydraulically actuated, oil-bathed, multi-disc brake. Because the wear is negligible, these brakes require no maintenance work. The driver has few controls: two direction levers and an accelerator. The driver has no gears to change, and he can select the automatic final reduction gear ratios while on the move. The set-up is extremely simple and the time necessary to train drivers is very much reduced. In emergencies, any of the other crewmen can take over from the driver. Tactical and Strategic Mobility The considerable reduction of weight and volume due to the elimination of a number of components reflects in the low battle weight of the vehicles: 8.5 tons for the Cobra41 MICV and 9.5 tons for the Cobra-90 AFV. This was notably ARMOR - I less than the U. S. Marine Corps' LA V (12.3 tons) eight-wheeled armored vehicle that has an equivalent degree of protection. Both foreign vehicles have a more compact configuration than the LA 1'. Nevertheless, the Cobra-41 can carry two crewmen and ten comhat troops. It has a transportation capability of seven cubic meters in volume; i.e. a ratio of useful-to-total volume of 7.5 to 10 (compared with the 4.9 to 10 for the MII3). On the other hand, the Cobra-90 has a three-man crew and it carries an ACEC-designed, electrically-driven turret housing the MECAR W-mm Kenerga gun. Both vehicles use identical automotive components. Due to this compactness, a C-5A "Galaxy" transport plane can carry a 16-APC infantry company and still have 60 tons to spare. A C141A can carry four Cobras, and a C-130 "Hercules" can carry two. Powered by a 190-bhp Cummins turbo-compressor diesel engine, both the Cobra-41 and Cobm-90 can attain 76 km/hon a level road and have a range of 6(x) km. The vehicle's speed in reverse is the same as in forward gear. The Cobra- 41 is rear-driven and the Cobra-90 is front-driven. The suspension of the latter is strengthened by hydraulic shock absorbers on front and rear wheel stations. The Cobra vehicles run on a reinforced rubber track of the double continuous band type. Designed by ACEC for minimal metallic friction, these tracks are 30 pcrcent lighter than metallic tracks. This track does not suffer from the track-throwing problems that plagued the U. S. MI14 during the 1W;Os. They also make the vehicles less noisy and allow them the necessary discretion for reconnaissance, antitank and enemy artillery observation missions. The light weight of the machines ensures easy

- - - -, - + 03 0 4 Left E - + IG dp Right E + ID Electrical schematic of the ACEC drive system for armored vehicles. going over loose or sandy terrain, with a,ground pressure as low as 0.4 kg/cm-. The Cobra-41 has a good amphibious capability without any preparation, thanks to two electrically powered hydrojets and the automation of its trim vane control. On the other hand, the Cohra-90 has amphibious capability with its flotation screen. The compact silhouette of the Cobra vehicles, their agility, and their capacity to instantly change into reverse give them a significant degree of additional protection. They are also easy to hide. No Longer a Dream Until recently, the application of an electric transmission to armored and tracked vehicles had remained an unrealized dream. Now, thanks to the possibilities opened up by recent technological advances, it is no longer a dream. The ACEC successful, reliable, and lightweight electric transmission opens up anew era in the design and development of tracked armored vehicles, making it easier to meet some of the design requirements. It will also provide a cost effective ratio superior to that of other types of transmissions. Thus, an electrically-driven combat vehicle becomes very attractive in terms of performance, reduced training time, and easier maintenance, making it a more economical and energy-saving war machine. Raymond Surlbmont is the Belgian correspondent for Defensa, the Spanish military review. The author of the book, Japanese Armor, he has also written for Jane's Defense Weekly, Tech-nologia Militar, Armada International, and Armor. He is one of the founders of the association which supports the Belgian Tank Museum in Brussels. I ARMOR - 39