Providing Soldiers the Decisive Edge

Providing Soldiers The Decisive Edge by Captain Curtis L McCoy and SFC(P) Michael I?. Womer, Sr. Yoti piill tip arid start to engage the em?rriy witli yotir riiairi grin. Siidderi-lv, voti hear a loiid bang. Yoti think yoti are hit, brit yoti arc obviotisIv alive. 77ie TC is screariiirtg: "Back tip, back iipl" You placc the trartsritissiort selector irt n?vene arid give the tank fir11 throttle, But riotliirtg Itappem. Yoii look up. It seerits like eveiy iridicator light iri the driver's coritparlriierit is lit. Yair Itit the reset btittori, brit still riatii-irig happens. Yoti can Itear the e~tgi~ic nirirtirig, but it wort 't irtcrcase iiorse-power according to the tlirottle respouse. Yoti look to the frott arid can see the enerity contirig yorir way. Yoii tell tire platoon sepcant that the tank is irt sonic kind of protective mode, biit the e~tgi~ie is still ninrting, Tile net? titirig yoti know, yoti are preparing rite tank for destnictiorr to prevent its iise by the eneiitv. In this situation, the survivability of a tank crew might well dcpcnd on the ability of the system to extricate itself from a hostile environ-mcnt, particularly aftcr taking a hit. In such circumstances, mobility, to include placing the transmission in gear, becomes paramount, even at the expense of increased probability of long-term damage to the engine or transmission. New SHAFTS system control levers, at left, allow manual override of an Ml's protective systems in combat. Two electronic systems that control throttle response and transmission drive range selection govern the mobility of the current M1 tank. The first major factor is the throttle response. An electronic control unit (ECU) that mcdilies the fuuel flow to the turbine+ regulates throttle rcsponse, depending on the driver's demands and the state of the engine. The unit has inherent algorithms callccl "protective modues" (PMs), which protect the engine - and these take precedence over driver commands. This prevents necdless damage to a malfunctioning engine in peacetime exercises. One such protective mode is called 14 ARMOR - March-April 1988

~ PM-Ill. When the ECU experiences a loss of electrical power - or Idieves it is sensing an engine fucl control malfunction - it throws the engine into idle and disconnects it from any further control. In this circumstance, the tank must operate with less than five percent of its available power, which effectively prevents it from moving. The crew can neither alter the fuel flow nor steer the vehicle when it is in PM-

111. lf the crew cannot reset the ECU, the system must be shut down. This neutralizes the tank's firepower and makes it likely that the system will not restart. The other major factor is the electronic control of the transmission. If the electrical signal is broken within the system because of any component Failure, the driver in a combat situation hlls no way to engage the drive train, even if the transmission is still functional. The only way to override this feature is to dismount under lire and attempt to push the forward drive plug in the rear of the transmission - not an option in combat. In battle, transient losses of electrical power or erroneous sensor readings resulting from hostile fire might cause a reasonably high Occurrence of PM-Ill or transmission malfunctions. In these situations, engine and transmission protection is a moot point. One must weigh the whole concept of protecting the power train during peacetime against the ramifications of possibly endangering the crew during combat. In July 1986, the science advisor to the Commander-in-Chief, U S Army Europe (USAREUR) and 7th Army, requested the Ballistic Research Laboratory (BRL), Human Engineering Laboratory

(HEL),

and the Ordnance Center and School (OC&S), at Aberdeen Proving Ground, Maryland, to investigate the potential of a "quick and easy" PM- 111 and transmission manual override Ti that would be used only in battlefield situations. The result of their efforts is the Shift Hand Actuated Fuel Transmission System (SHAFTS) on the M1 tank. This system provides the M1 Vank a marked improvement over its current limp-home capabilities. The concept was to make the entire tank hull operational in a manual mode if required after an engine start cycle was cornplcte. Second, the tank driver had to be able to opcrate this emergency system without exiting the tank under combat conditions. Additionally, thcre would have to be protection against frivolous peacetime use. The SHAFTS that was proposed. to offer an improved limp-home capability has essentially three subsystems: 0 A mechanical fuel metering valve (Fig 1). 0 A mechanical transmission shifter (Fig 2). 0 A two-lever control box (Fig 3). The mechanical fuel metering valve for rebwlating fuel flow to the Ml's gas turbine en-Fig 1 Mechanical fuel metering valve assembly Fig 2. Mechanical transmission shifter assembly Fig 3 Two-lever control box at driver's station actuates cable links to engine. Fig 4 A full view of the transmission valve body shows transmission solenoid tripping mechanisms mounted at lower left. E M O R - March-April1988 75 I gine consists of two hypnss hoses connected to a fuel-metering valve, which permits a flow rate from zero to approximately 238 pounds per hour (PPH). A control arm with 90- degree rotation mounted in the driver's compartment actuates the valve. This allows fuel to bypass the engine's hydro-mechanical unit (HMU) during a PM-Ill. The bypass metering valve controls pressurized fuel provided by the HMU's high-pressure pump. The high pressure fuel is available at the "Pl" test port on the HMU. The manual fuel metering valve, which is closed during normal operation of the vank's fuel supply system, permits injection of a metered amount of fuel into the "P3" test port on the HMU. This fuel is directly injected into the gas turbine engine's combustion chamber. The restricting orifice controls the maximum volume of the valve's control arm. The driver remotely controls this arm through a flexible cable and control box. The valve's orifice was selected to permit a rnax-imum fuel flow of approximately 335 PPH in PM-Ill, yielding an engine output of approximately 400 hp. The valve/orilice arrangemcnt permits engine output (and vehicle speed) to go from zero to the maximum output permitted by the valve. The manual transmission shifter for regulating the electronic solenoids within the transmission valve body assembly consists of a solcnoid-tripping mechanism (Fig 4), connected to a cable from the driver's station. The tripping device operates the electrical solenoids within the automatic transmission, thereby permitting mechanical transmission operation without the need for clectrical power. The mechanical control on the transmission (Fig

2) does not interfere with the electrical functioning of the valve body. A disconnect device in the mechiinical arrangement separates the mechanical control from the electronic system. The result was a tripping mechanism with four positions: drive, reverse, neutral, and unlock. The tripping mechanism raises the check balls in each solenoid in the required combinations. The two-lever control box (Fig 3), used in conjunction with a manual flow and manual transmission shifter (Fig 2), permits control of both fuel flow and transmission shifting without electrical power. The interlocking device prohibits increasing fuel flow above the 72-horsepower limit undcr PM-111 conditions unless the driver places the transmission into a drive gear. Conversely, the transmission may not he taken out of a drive gear unless the fltd llow rate is returned to the corresponding 72 hp. During combat operations, the driver can accomplish this. In December 1986, the SHAFTS tcchnical data package was delivered to MACOMs fcjr evaluation. The end result was a possible solution to the user's requirement request to increase the Ml's mobility survivability on the battlefield under a PM-111 condition or possible transmission failure. Thanks to the soldier and the chain of command, the Army Materiel Command's Ficld Assistance in Science and Technology (FAST) program and the US. Army Tank Automotive Command TACOM addressed this potentially hazardous operating condition.. Captain McCoy was commissioned in Armor at the USMA in 1978 and completed the Armor Officer Basic and Advanced Courses, the Motor Officer Maintenance Course at Ft. Knox, KY, and the Airborne, Ranger, and Infantry Officer Advanced Courses at Ft. Benning, GA. He also completed the German Airborne School, and the Combined Arms and Services Staff School at Ft. Leavenworth. He has served as a tank platoon leader, cavalry squadron and battalion motor officer, tank company XO, tank company commander, and is currently an armor research and development coordinator at the Ballistic Research Laboratory,

APG, MD.

Sergeant First Class Womer enlisted in 1973 and is a graduate of the Armor NCO Basic and Advanced Courses, the M60A1 /A3 Master Gunner Course, the M2/3 Commander's Maintenance Course, Fundamentals of Counseling course, and the Instructor Training Course. Among other positions, he has served as battalion master gunner, 2d Bn, 64th Armor; and brigade master gunner, 1st Bde 3d ID. He is currently assigned as the master gunner/NCOlC of the U.S. Army Ballistic Research Labor-atory, APG, MD. ~~ 16 ARMOR - March-April1988