Brig Ashish Bhattacharyya (Retd.)
In present context mobility, survivability and cost, innovative and disruptive solutions are necessary to ensure the operational viability of the next generation of Armoured Fighting Vehicles. The author elaborates as to how improvements in Electric motors technology (Traction Motors), regenerative technology and Energy Storage Devices can improve the functional efficiency of existing inventory and pave way to future developments.
The developmental trend till recent past in Armed Fighting Vehicles (AFV) including Infantry Combat Vehicles has been towards increasingly heavy, mobility compensated by higher power pack and ever more expensive combat platforms, to optimize the race between protective Armour and Anti-Tank weapons. The weight of armour and weapons, coupled with growing performance demands, have forced the engines to become larger and the vehicles themselves heavier. In present context mobility, survivability and cost, innovative and disruptive solutions are necessary to ensure the operational viability of the next generation of armoured fighting vehicles.
In a typical Infantry Combat Vehicle (ICV)of the BMP-II type, the driving compartment is located in the frontal part of the vehicle. It accommodates the driver and one soldier. The driving compartment is outfitted with observation devices, directional gyro, vehicle steering levers, instruments, actuating devices and fire-fighting equipment. The engine compartment is located parallel to the driver in the frontal part of the hull. The turret is located in the middle of the hull, just ahead of the engine compartment. It sports a 30mm Cannon, an Anti-Tank Guided Missile (ATGM) launcher and a co-axial machine gun. The commander and the gunner are positioned in the turret. The troop compartment is located in the rear of the hull between the port and starboard sides. It is divided longitudinally into two sections by the central fuel tank and a container, which holds electrical equipment. The troop compartment has 6-9 seats for the mounted personnel: three- four seats in each section. Most of these are sub20-24 Ton category and are amphibious, which is one of the most important characteristic desired by Users, especially for obstacle ridden terrain exploitation.
The design of a traditional 8×8 APC of the types of BTR/TOPAZ, are also amphibious and are is built around “this big, monolithic block of the engine and complex space claiming the drive train”. The passenger compartment is built over this drive train typically forcing the troops to sit with legs over the drive shafts and their feet on the differential cases. Not only does that arrangement make protecting the bottom of the vehicle difficult, but it also potentially risks turning elements of the drive train into lethal projectiles in the event a mine or IED explodes underneath. Modern wheeled APCs design have their fuselage shaped in a V- configuration that deflects blast energy somewhat, but the dangers listed above, still remain, albeit to a lesser degree. Breaking away from the need to design the vehicle around the drive train, the armoured vehicle can become both more comfortable for their occupants and most importantly, much better defended against detonations beneath the floor-pan by providing space for added protection.
Issues with Current BMP2 Transmission
The engine and transmission are to the right of the driver's compartment with the air inlet and outlet louvers on top of the hull. Indian BMP-2 is motorized with a four-stroke, six-cylinder Model UTD-20 supercharged diesel engine developing 285/300 hp at 2,600 rpm. Diesel Engine drives the track system through a hydraulically assisted, mechanical gearbox and a mechanical transmission. The torsion bar suspension of BMP-2 consists of high tensile special alloy bars, fixed at one end to the hull and a road wheels arm at the other. A dead axle road wheel is mounted on the far end of this arm. Six such road wheels are placed on each side. The drive sprocket is at the front and return idler at the rear with three track-support rollers on top. The upper part of the suspension is protection by armour plates. Some of the known disadvantages of transmissions are:
- Maintenance intensive
- Bulky -No extra space left for updates on the platform
- Prone to reliability issues due to quality of seals and gaskets etc.
- Not conducive to Hybrid platform adaption in future
- Lower maneuverability due to inherent interlinking of drive shafts to hydraulic transmission.
- Bulk leads to weight increase, which needs higher power density engines with better cooling systems which further adds to overall weight.
Hybrid Electric Vehicles
While experiments with electric combat vehicles started as early as 1943 (US T-23 tank), workable solutions emerged only post 2000. The drive for using Electric Drives for Combat Vehicles centered mainly around reducing bulk and weight of the power train leaving more headroom for added protection and better survivability, other outcomes being stealth operation, good torque-speed response From pure electric to Hybrid Electric Vehicle (HEV) of the Parallel and Series category, Electric Drives have come a long way. The Future Combat System (FCS) and Joint Light Tactical Vehicle (JLTV) in the US, Future Rapid Effects System (FRES) in the UK, SpiterskyddadEnhets Platform (SEP) in Sweden, the M-84 upgrade of Croatia and Tracked Combat Hybrid Electric Vehicle (T-HEV) of ATLA-MOD in Japan, all highlighted the advantages arising out of use of Hybrid Electric Drive Systems in both Wheeled and Tracked Military Ground Vehicles. These advantages included:
- Improved Mobility and Fuel Economy (upto 40%)
- Silent Mobility
- Silent Watch Capability
- Enhanced onboard power generation for ever increasing demand from electric and electronic systems
- Improved design flexibility with reduced weight
This has become possible due to huge improvements in Electric motors technology (Traction Motors), regenerative technology and Energy Storage Devices. Electric motors do away with the need for a mechanical linkage between the engine and the drive wheel or sprocket. In addition, Electric motors have a high torque-speed profile for the traction of combat equals i.e. high torque at the acceleration, climbing and turning and a wide range of high power. Some of these programs are discussed below
Ground Combat Vehicle (GCV) Programme
A known upgrade in the direction was the United State Ground Combat Vehicle (GCV) programme prototype equipped with the MTU Series 890 R6 engine and hydro pneumatics suspension one of the pioneering effort in this direction. The Drive enables fundamental changes in vehicle configuration as the engine and transmission do not have to be connected mechanically enabling increased flexibility in the choice of power sources and their location, facilitating easy introduction of fuel cells and advanced battery / energy storage technologies. Also the Internal Combustion Engine (ICE) (to run Generator) can be operated at optimal range, achieving greater fuel saving.
The E-X-Drive Transmission, a key component of a Hybrid Electric Drive Propulsion System, minimized the electrical demand, saves on vehicle fuel costs, improves maintainability and reliability, provides higher dash speed and acceleration and increased on-board and off-board power. The E-X-Drive transmission systems delivered 10% to 20% more fuel efficiency than a conventional mechanical propulsion system. Unfortunately, this program was dropped in Feb 2014 due to cost considerations resulting from some unrealistic specifications.
The Japanese T-HEV program used a Series Hybrid System. As the primary power source, the mechanical power of the ICE is converted into electrical power by a permanent magnet synchronous generator which produces 3-phase AC power. This AC power is converted into DC power by a converter and provided to the DC power bus (600 volts). As the secondary power source, Lithium ions Batteries directly provide DC power to DC power bus. DC power from these two sources are combined and provided to the inverters where it is again converted into AC power which drives the permanent magnet synchronous motors for propulsion.
In Wheeled Combat Vehicles, by swapping the conventional diesel engine for a diesel generator, and drive shafts, differentials and transmission systems for powerful and compact electric motors that fit entirely within available space, one can significantly reduces platform weight and open up a range of new possibilities for vehicle design. The hub-drive fits on the suspension system. Retrofitting the hub-drive system to an existing multi-wheel infantry vehicle could bring power and agility gains through the lowered overall platform weight, or conversely allows it to carry greater armour, additional equipment or more personnel while keeping within optimum floatation weight. All-wheel drive electric hub motors also allow for effective torque vectoring, routing more power to the rear to climb hills, for instance, or alternatively using it to pivot the vehicle around in difficult terrain.
Potential BMP2 Transmission
The BMP-2s on the inventory of the Indian Army are nearing the end of their service life. The FICV program is still to get a green signal from the MoD. As an interim measure a program to upgrade the mobility and firepower capability of this platform to give it a new lease of life, had been undertaken. After vacillating between comprehensive upgrade and systems upgrade, number of private industries are competing in this program under the latter. Any conventional upgrade will come with its associated weight penalty to the BMP which is already reaching the limits of its floatability envelope. Though adding floats on the sides/bottom could mitigate this challenge, it would make the BMP more voluminous and thus present a bigger target in the battlefield in addition to logistic challenges.
World is already headed towards Electric/Hybrid transmission in Civil & Military applications. India too is not far behind especially in the component and systems manufacture for Electrical Vehicles (EVs). It may be worthwhile to examine the feasibility of trying out Hybrid Electric Technology for the mobility upgrade for the BMP. With active support and scaling up of the vibrant existing industry in India and some support from established OEMs in the field, we may be rightly placed for an indigenous HEV solution for life extension of the aging BMP-2 fleet. Some of the envisaged advantages are:-
- Lighter weight of BMP2 aiding increased survivability through added protection as also retention of floatation in spite of major capability enhancement
- More maintainability and reliability
- Better acceleration and maneuverability
- Easy crew interface for control
- More Space for modifications and add on systems
- Spare electric power for Aux applications/ systems/ weapons
- Continuous and independent control of tracks providing acute turn radius
- Fuel saving due optimization of engine for power generation and high efficiency of electric transmission
An added and important spinoff - this would help mature the HEV support industry in time for the FICV in its new avatar (presumably through the Make-II or SP route).