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A monthly house bulletin of Defence Research & Development Organisation ■ Vol. 31 No. 7 ■ July 2011ISSN : 0971-4413BULLETIN OF DEFENCE RESEARCH AND DEVELOPMENT ORGANISATION Vol. 22 No. 2 April 2014

Armoured Fighting Vehicles (AFVs) play an important role in any war

scenario. Particularly, the Main Battle Tank (MBT) being the highly survivable and lethal combat vehicle, play as a game-changer in conflict situations worldwide.

Combat Vehicles Research and Development Establishment (CVRDE), a constituent l a b o r a t o r y of DRDO in Chennai, is e n g a g e d in design

and development of armoured fighting vehicles and specialised vehicles to enhance the combat capabilities of the Indian Army. Apart from design and development of the most prestigious product Arjun MBT, CVRDE has developed various tracked vehicles and associated technologies and sub-systems for AFV applications.

This special issue of Technology Focus brings out an overview of some

of the technologies and sub-systems

developed by CVRDE for AFV applications.

Indigenous Technologies and Sub-systems for Armoured Fighting Vehicles

2 April 2014

From the Desk of Guest EditorArjun MBT is a flagship

product of CVRDE. The other armoured vehicles developed by CVRDE, which have gone into production are: Armoured Patrol Car, Armoured Recovery Vehicle, 130 mm SP gun–Catapult on Vijayanta, Carrier Mortar

Tracked Vehicle, Carrier Command Post Tracked and Missile Carrier Vehicle for Integrated Guided Missile Development Programme (IGMDP) on BMP-II, Bridge Layer Tank (BLT-72), Combat Improved Ajeya and Armoured Ambulance. CVRDE has successfully developed Unmanned Ground Vehicle based on BMP-II platform for surveillance, NBC reconnaissance and mine detection purposes. During late eighties, CVRDE designed and developed Aircraft Mounted Accessory Gear Box (AMAGB), Aircraft Bearings, PTO Shaft, 5 kW Brushless DC Generator and Hydraulic Filters for LCA Tejas. CVRDE has also enhanced its infrastructure through creation of test facilities for engine and suspension systems of AFVs, state-of-the-art EMI/EMC Test Facility as per latest standards and has developed Training Simulators for Arjun MBT Drivers and Gunners.

Arjun MBT, the brain-child of CVRDE, has been designed to meet Army's most stringent requirements and provides high mobility, superior firepower, enhanced protection and crew comfort. Two regiments of Arjun MBT Mk-I have been inducted into Army. Based on the expertise gained, Arjun MBT Mk-II has been developed with enhanced performance which includes Missile Firing Capability, Improved Commander’s Panoramic Sight, Track Width Mine Plough, Automatic Target Tracking,

Power Driven Air Defense Gun, Advanced Running Gear System, Final Drive with reduction ratio, and Improved Slip Ring. The improved performance of Arjun MBT Mk-II has been successfully demonstrated to the user.

On the technological front, CVRDE has excelled in a gamut of technologies related to Combat Systems which include In-Vehicle Networking with Multi-Bus Architecture, Inter Vehicle Information System, Electronic Fuel Injection System, Commander’s Panoramic Sight, Advanced Fire Control Computer, Laser Warning and Countermeasure System, Digital Image Exploitation System for the driver including Stereo Vision, Image Fusion and Map display, Indigenous Fiber Optic Gyros and ATE for Compact Electronics Unit, All Electric Drive, 400 hp Electronically Controlled Power pack for BMP-II. CVRDE is currently working on projects such as Arjun Armoured Repair and Recovery Vehicle (Arjun ARRV) and Armoured Vehicle Engineering (AVE). The establishment is spearheading the National Mission Project for Development of 1500 hp Engine and Transmission.

Technology Focus is the medium through which we get the opportunity to create awareness about the technologies developed by DRDO. A special issue on ‘Indigenous Armoured Tracked Vehicles’ was brought out in June 2011. This issue gives an overview of some of the technologies developed for AFV applications by CVRDE.

Dr P Sivakumar

Outstanding Scientist Director, CVRDE

3April 2014

Air Cleaning System for Armoured Fighting Vehicle

In Armoured Fighting Vehicle (AFV), the space is at premium especially in the engine compartment. The powerpack of an AFV consists of an engine coupled with transmission and peripheral systems like cooling system, air filtering system, and under armour fuel tanks. Even though the air cleaning system is a static system, it is important as well as critical for the better performance of the engine. While in off-highway terrains, the dust contents in the atmospheric air are of the order of 1 mg/m3 to 40 mg/m3, in the desert it is considered to be in the order 2000 mg/m3. Moreover, ambient temperature in the desert terrain is often around 50o C. Thus requirement of air filtration in desert terrains is enormous and the air filtering system of the AFV should filter down the air to 3-5 microns in order to supply clean air to its engine. Also, air filtration system of an AFV shall filter the combustion air up to a specified level, provide maximum efficiency, offer lesser pressure drop, extract positive dust so that engine works to its optimum level. CVRDE has developed the following air filtration systems:

Air Filtration System for T-72 Base Engine

The two-stage air filtration system of a T-72

base engine consists of a primary cyclone filter and a

secondary barrier filter element. While the primary filter

is with reverse flow cyclones, secondary filter is a wet-

type wire wool cartridges. A pressure sensor indicates

the status of contamination in the driver’s panel. The

dust collected from the primary cyclone filter is drawn

by exhaust scavenging.

Air Filtration System for Up-rated T-72 Engine

CVRDE has up-rated the power output of the T-72 engine from 780 hp to 1000 hp by modifying the peripheral sub-systems. Development of under armour air filtration system for up-rated T-72 engine was taken up with the help of Indian industry. The air filtration system of the up-rated T-72 consists of a primary filter with unidirectional flow cyclones and a disposable secondary filter with dry-type resin impregnated or equivalent paper filter elements. The air filtration system has been configured within the available space in T-72 engine compartment and consists of the following major components: primary cyclone filter assembly; secondary filter elements; filter housing assembly; scavenge fan assembly with cable and duct; and differential pressure sensor and status indicator.

The Primary cyclone filter, the pre filter with unidirectional flow cyclones, filters heavier dust particles. The secondary filter elements filter the air

Figure 1. Primary filter

up to 3 microns with an over all efficiency of 99.99 per cent. The combat filter is easily replaceable/cleanable. Primary cyclone filter and secondary filter elements are housed in a filter housing assembly. Scavenge fan assembly with cable and duct—a positive dust extraction system consisting of an axial fan driven by an electric motor—removes the heavier dust particles filtered by the primary cyclonic filters. Differential

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pressure sensor and status indicator sense and indicate

the pressure drop across the air filtering system in the

driver’s panel.

Choking condition of the secondary air filter

elements is indicated by the signal provided by the

vacuum switch, which operates at the prescribed

limit. Full load running is possible only by cleaning the

secondary air filter elements or by replacement of the

elements.

Technical Specifications: Air filtration System of Up-rated 1000 hp Engine

Air filter type : Dry

Number of stages : Two

Primary filter : Uni-flow cyclones

Cyclone material : High density poly propylene Airborne dust concentration : 2 gm/m3

Dust extraction : Positive dust extractor fan 28 V, 40 amps DC Purge rate : 10 per cent of main flow

Secondary filter : Resin impregnated element paper filter or equivalent

Surface area of filter paper : 40 m2

Least particle size : 3 microns absolute to be filtered

Air flow rate : 1.33 kg/s Filtration efficiency : 99.99 per cent (SAE Coarse)

Pressure drop : Clean air 250 mm WG After choking 760 mm WG

Figure 3. Assembly Air Cleaner

Figure 4. Scavenge fan assembly

Figure 2. Secondary filter installed in casing

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The air filtration system with up-rated 1000 hp engine has been integrated in T-72 vehicle and trial evaluated for more than 2000 km for satisfactory performance.

Figure 5. Air filtration system integrated in vehicle

Cooling System for AFVs Armoured fighting vehicles are powered by high

specific output diesel engines. To dissipate the heat rejected by engine coolant, engine oil, and charge air and transmission oil, compact cooling system is used in modern AFVs. AFVs in India, often operate at ambient temperature higher than 50° C. Space is premium in AFVs as any increase in volume of the sub-systems will lead to increase in weight. Therefore proper configuration and design and development of cooling system for AFVs is very critical.

Cooling system of an AFV dissipates the rejected heat at all operating temperature. The pressure drop through the system has to be kept minimum to reduce the pressure head developed by the coolant pump and cooling fans, which should be efficient to reduce the power consumed by it.

Development of cooling system for operation in Indian environment is a very challenging task. CVRDE has established technology for configuring and developing cooling system for AFV applications. Number of compact aluminum plate and fin matrices with higher heat transfer surface area per unit volume have been developed and adopted in various heat exchangers utilising the infrastructure and expertise available within India.

The cooling system has to meet the cooling requirement up to 55° C. The aluminium plate and fin matrix used by CVRDE for the cooling system has higher heat transfer area per unit volume up to 1800 m2/m3 compared to that used in commercial vehicles (1100 m2/m3). The flow rate and head required by the fan is very high for a given volume, hence efficient and high speed cooling fans have been used. To reduce the pressure drop in cooling air, ducted cooling system has been adopted as it also enables the vehicle to undergo medium fording.

Due to space limitations, it is not possible to provide cooling capacity up to 55° C. Hence to control thermal load on cooling system, CVRDE has incorporated automatic power regulation based on coolant temperature at higher ambient temperature.

In modern AFVs, heat exchangers like engine oil cooler, charge air cooler, transmission oil coolers are placed inside the powerpack compartment and are cooled by coolant. Only radiators are placed on the top of the powerpack and are cooled by the atmospheric air. CVRDE has developed variety of compact aluminium plate and fin matrices for application in indigenous powerpack. Multi-louvered fin and offset strip fin (parallel) with heat transfer area per unit volume in the range 1100-1700 m2/m3 have been developed. The

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following heat exchangers have been developed using these fins:

A 720 x 880 x 120 mm radiator with 380 kW heat adissipation capacity

A 430 x 280 x 210 mm charge air cooler with 150 kW aheat dissipation capacity

A 500 x 200 x 76 mm LH and RH transmission oil acooler with 75 kW heat dissipation capacity of each

A 325 x 225 x 50 mm fuel cooler with 10 kW heat adissipation capacity

evaluated and optimised in both test rig and vehicle.

This compact cooling system technology can also be adopted for civil and aircraft applications where volume and weight is very critical.

Cooling System for T-72 VariantsDeveloping cooling systems, especially for the

engines of AFVs, to meet the rigorous environmental conditions of high temperature and dust, have always been challenging to Indian AFV technologists. Projects connected with T-72, like Bridge Laying Tank (BLT) T-72, 1000 hp engine upgrade and Ex Tank, have necessitated optimally designed higher capacity cooling systems within the same spatial envelope of T-72 powerpack configuration.

The radiators and engine oil coolers, the cooling fan and the cooling water pump combined with the ballistic grills for air flow are the key aggregates/components of the system. The indigenously developed cooling system components would go into the regular series production of BLT T-72. The associated technologies and cooling product developed are discussed herewith.

Heat Exchangers—Water radiators and Engine Oil Coolers

The radiators and coolers originally used in the T-72 were grossly inadequate for effective cooling in BLT T-72 under summer desert conditions. After experimenting with different sizes of core thickness,

Figure 6. Clockwise from top left: Radiator, charge air cooler, transmission oil cooler LH and transmission oil cooler RH

The cooling fan of an AFV has to ensue cool air flow with the specified pressure head overcoming resistances in the cooling air flow passages. Since it requires to run at 5500 rpm, its radiographic quality needs to be very good and the fan has to be dynamically balanced. The cooling fans for AFVs have been developed indigenously.

The cooling system, consisting of all the above heat exchangers and cooling fan, has been integrated with indigenous powerpack. The system has been

Figure 7. Cooling fan

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the radiators and oil coolers have been successfully developed indigenously using aluminium core, plate and fin type, furnace brazed with single pass liquid flow between headers. These were tested extensively under simulated conditions and by installation inside tanks.

Technical Specifications: Radiator LH and Radiator RH

Heat dissipation : 105 kW each

Coolant flow rate : 500 lpm

Coolant inlet temperature : 115° CAllowable coolant

pressure drop : 0.5 bar

Cooling air flow rate : 2.50 kg/sCooling air inlet

temperature : 65° CAllowable pressure drop

on cooling air : 35 mm WG

Size of core matrix : 927 x 470 x 130 mm

Figure 8. Oil cooler LH (top) and Oil cooler RH

Technical Specifications: Engine Oil Cooler LH and Engine Oil Cooler RH

Heat dissipation : 60 kW each

Oil flow rate : 180 lpm

Oil inlet temperature : 120° C

Allowable pressure drop on oil : 1.7 bar

Cooling air flow rate : 2.50 kg/s

Cooling air inlet temperature : 50° C

Allowable pressure drop on cooling air : 35 mm WG

Oil used : SAE 20 W 50

Size of core matrix : 610 x 460 x 63 mm

Cooling Water Pump

A high capacity centrifugal cooling water pump has been indigenised for T-72 engine based variants including BLT T-72. The pump made of aluminium alloy is mounted on the tank’s engine and in the same spatial and originally mounting configuration. The pump has been precision manufactured with a high-speed impeller and mechanical seal. Prototype samples have been tested at Engine Factory Avadi’s test facility. Installation on the engine also has been tried out. The design is being fine tuned and development work is in full swing.

Technical SpecificationsType : Centrifugal pump

working in closed loop system

Body material : Aluminium alloy casting or its equivalent

Input drive : Mechanical

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Pump speed : 3000 rpm normal max.Pump outlet : 610 lpm @ pressure

≥ 0.4 barMaximum water

temperature : up to 115° C

Cooling FanA centrifugal cooling fan with aerodynamic

vanes has been developed indigenously for T-72 configuration. Unlike the riveted aluminium sheet construction, the fan has been made using casting and other forming processes. Sand casting, ring rolling followed by CNC machining and Low-Pressure Die-Casting (LPDC) processes are also being worked

out. The first two have been established and third technology is in the development mode. The fans have been bench tested for high speed running, flow, and power consumption. The sand cast and ring rolled fans have been tested on prototype tanks and found compatible.

Technical Specifications

Material : High grade aluminium alloy

Overall diameter : 655 mm

Height : 205 mm

No. of vanes : 16 equally spaced

Ballistic Grills

Original table-top type louvres used in T-72 grills (over the radiator) have been replaced by a different type of section, which permits almost double the air flow and less obstruction, but retains the ballistic properties. The louvre sections have been formed from armour grade EN 25 steel by special hot extrusion method and other finishing processes. Grills (length: 460 mm; Breadth: 50 mm and thickness: 4.5 mm) made with this section, have been tested as per approved standards and found ballisitically superior.

Electronic Fuel Injection SystemConventional fuel injection pumps used in up-rated

1000 hp engine do not have features for regulating fuel as function of charge air temperature, coolant

Figure 9. Cooling water pump

Figure 10. Cooling fan

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temperature and shutdown mechanism for low engine oil pressure and low coolant level. These features are essential for operation at high ambient temperature and also for foolproof engine performance. CVRDE has developed Electronic Controlled Fuel Injection System (ECFIS) jointly with Indian Institute of Technology, Chennai, to introduce electronic governor in place of mechanical governor, to develop microprocessor-based engine controller unit and to introduce actuator to regulate the fuel delivery for up-rated 1000 hp engine.

The ECFIS consists of sensors, actuators, control system and software. The system senses engine speed, load, charge air temperature, coolant temperature and accelerator pedal position. The input data is fed to electronic controller, which gives signal to the actuator and that in turn moves the control rack. Indigenously developed microprocessor-based controllers and actuators have been integrated with the fuel injection pump (FIP) and evaluated in FIP test bench. FIP integrated with the engine has also been evaluated in the test bed. The system successfully controlled

the fuelling based on charge air temperature, coolant temperature, etc., and met all the system requirements.

Up-rated 1000 hp Engine for T-72 Tanks

T-72 M1 tanks are powered by 780 hp engine. It is a V type, 12 cylinders, four stroke, water cooled, direct injection and mechanically supercharged engine having 38.88 liters of swept volume. To meet the Indian operating environment conditions, its power output has been upgraded from 780 hp to 1000 hp to enhance its mobility with the increased weight.

Figure 11. ECFIS installed in the FIP test bench

Figure 12. Up-rated 1000 hp Engine

Power enhancement was achieved by introduction of turbochargers in place of mechanical super charger; modification in the fuel injection system; introduction of charge air cooling; introduction of enhanced capacity water and oil pumps; introduction of new exhaust manifold corrections and by modifying existing inlet manifold.

The engine performance has been evaluated and demonstrated on the engine test bed. Prototype engines have been subjected to 100 hours of full load test and 400 hours of endurance run. Details of upgraded module are as follows.

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Engine Peripheral Systems for Vehicle Integration

To cater for the requirement of up-rated 1000 hp engine, the following modifications were carried out:

Introduction of compact aluminium plate and fin aheat exchangers in place of brass/copper tube and fin type heat exchangers consisting of radiators, engine oil cooler and transmission oil cooler

Introduction of efficient aluminium aero foil profiled acooling fan in place of fabricated cooling fan

New air cleaning system consisting of cyclonic aprimary filter, paper fine filter and positive dust extraction system

Efficient engine oil filter a

Positive closed breathing system a

Teflon corrugated stainless steel hoses in aplace of rubber hoses for engine oil lubrication connections.

The prototype up-rated 1000 hp engine after evaluation at CVRDE test bench has been integrated in a T-72 M1 vehicle. The vehicle field evaluation has been conducted at Avadi trial site as well as

in Rajasthan. Most of the vehicle trials have been conducted at Rajasthan as it warranted to prove the engine qualification at higher ambient temperatures and at dusty environmental conditions. The engine has successfully completed user trials at Pokhran and validation trials by DGQA and MAG-6.

Sub-Systems for Gun Control SystemAutomatic Target Tracker

Automatic Target Tracker (ATT) is used to assist gunner in automatically slewing the GMS mirror to the selected target. ATT automatically tracks the selected target using video available from the sighting system. A prototype ATT has been developed and evaluated at trial sites in and around Chennai, and at Suratgarh. The ATT takes video input from the monitoring port of GMS and swaps command signal of Gunner’s Control Handle (GCH) in auto mode. This set-up, integrated on the tank, has been satisfactory evaluated and recommended by the users. ATT was trial evaluated at MFFR in the static observer to moving target, moving observer to static target and moving observer to moving target modes.

Figure 14. Automatic target tracker unitFigure 13. Up-rated 1000 hp engine with air filtration system

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Trials were conducted in both, day and night, for a range of 2 km and expected pixels accuracy was achieved.

Salient Features

Relieves stress and fatigue of the gunner a

Tracks the target during obscurations and even in athe cluttered environment.

Handy in undulation terrain, viz, desert area. a

Digital Controller for Weapon Platform Stabilisation

Main function of the Gun Control System (GCS) in an AFV is to provide STAB (self-stabilisation) and accurate slaving of the weapon platform to a stabilised sighting system in spite of terrain disturbances. The stabilisation and slaving accuracy should be below the permissible limit to achieve high first round hit probability while firing in static/mobile modes. This demands a highly precise controller for weapon platform stabilisation.

The controller unit is the heart of a GCS which houses all the electronics for control law implementation. Basically the controller works in STAB and SLAVE mode. In the electro-hydraulic GCS, the electrical output from the control handle drives the turret and gun through the servo valves. In the STAB/SLAVE modes of operation, the controller unit controls the hydraulic flow to the actuators. In the STAB mode of operation inertial stabilisation to the gun is provided by counter moving the gun/turret to the hull movements due to terrain disturbances. In the SLAVE mode of operation, the gun is slaved to the master stabilised sight. Position error signals through resolver chain system are fed from the Fire Control System (FCS) to GCS. This mode is the primary mode of operation of Integrated Fire Control System (IFCS).

CVRDE has developed a compact digital controller to achieve high first round hit. The digital controller has some inherent advantages; modification of filter parameters is easy as these are not designed through discrete components and the software filters are not dependent upon age or environmental factors and provides flexibility in altering the coefficients without any hardware changes. The digital controller unit is compact and can be implemented with minimum hardware.

The controller is built with state-of-the-art digital signal processor with high-speed 16 bit ADC and DAC. Bilinear transformation technique has been used to implement various compensators in digital domain. The controller also comprises effective anti-aliasing filters. The sampling frequency is optimally selected at 4 kHz.

This system also provides both on-line and off-line Built-in testing equipment (BITE). During system on, the on-line BITE gives health of the controller unit. The system also provides an off-line/manual BITE, wherein

Figure 15. Digital controller

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a reference signal is fed instead of the control handle signal and Linear Variable Differential Transformer (LVDT) signal is compared with a known reference. The system has provision of recording predefined events and time stamping of the same.

The digital controller comprises power supply module, power supply and control logic module, and DSP module. Additional functions of MIL-1553B and Ethernet have been provided for digital communication with other systems of the weapon platform.

The controller has been designed and developed to the stringent specifications and qualifies ESS and EMI/EMC tests. It has been thoroughly tested on bench and then on tank before subjected to firing trial. This unit was integrated with other sub-systems of the weapon platform and underwent summer firing trials in Rajasthan. Excellent results were achieved in both static and dynamic mode of firing.

Suspension System for AFVs

Hydro-Gas Suspension System

Main Battle Tank (MBT) is a cross-country vehicle with high mobility and superior ride comfort along with other main characteristics like superior fire power, high degree of protection, etc. Higher mobility power is essential for an MBT vehicle to negotiate and manoeuvre faster in terrains such as hard and soft grounds, ditches and steps, water obstacles and marshy patch, sand dunes and mountains in circumstances having rapid dispersion of fighting forces during execution of counter attacks from unexpected directions. A well-matched running gear system is very essential to make use of the maximum torque available at sprocket through power train from engine.

CVRDE has indigenously designed, developed, tested and productionised sub-systems, viz. Hydro-gas Suspension Unit (HSU), track adjuster, twin top roller, tracks and assembly road wheel for Arjun MBT. All these sub-systems have been subjected to elaborate field trials in different terrain condition for around 70,000 km run and proven for their performance and expected life. Besides, the variants of suspension system, viz., in-arm hydro-gas suspension, tandem strut for Ex-tank, hydro-gas strut for BMP, hydro-gas strut, have also been successfully designed and developed for heavy commercial vehicle and hydro-gas strut for naval applications.

Figure 16. Running gear system/sub-systems mounted on tank

Hydro-gas Suspension Unit The suspension system is intended for cushioning

the impacts, shocks, and for damping the oscillations of the hull when the vehicle moves over irregularities of the terrain and also when obstacles are being negotiated to provide crew comfort, protecting the sensitive on-board equipment and also to provide stable platform for armament thereby improving fire performance accuracy.

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A modular HSU has been realised to meet the functional requirements of the hydro-gas suspension system.

The HSU consists of actuator and accumulator cylinders with sliding piston, floating piston and in-built damping unit, crank assembled with piston rod, axle arm assembly, cover assembly and road wheel pair. Vehicle load is transmitted through the road wheel support and trailing axle arm to the suspension unit. The wheel loads are transmitted by means of a crank pin with splined shaft, which is a structural extension of the axle arm assembly through crank and piston rod assembly to the HSU. By means of movement of sliding piston and, thus, the oil through damper unit, the vibration of vehicle is damped out. The gas under high pressure in the accumulator cylinder acts as spring. In the HSU, the main bearings are located internally in the crank case, which is sealed to the atmosphere and is independent of the axle arm assembly.

HSU｜Technical Specifications

Spring characteristics : a Non-linear spring through gas medium

Damping : Bi-directional in-built a damping

Wheel travel : 535 mm a

Static load : 4.2 ton a

Dynamic load : 19 ton a

Oil used : SAE 10 W 30 a

Gas used : Nitrogen a

Application : Arjun MBT, 14 stations a per vehicle.

HSU｜Salient FeaturesLarger wheel travel possible a

Good ridi a ng comfort due to non-linear spring characteristics

Provide stable gun platform for firing on the move a

Ease of maintenance a

Low silhouette of vehicle a

High effective inside volume aPressure and spring rate can be independently aadjustedFigure 17. Schematic diagram of HSU with its parts

Figure 18. HSU for Arjun MBT

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In-built damper units for better damping distribution apossible

High cross-country mobility a

High-Pressure Piston Seals for Hydro-Gas Suspension System

The HSU uses high-pressure piston seals to exhibit greater sealing efficiency in dynamic loading at various operating conditions, viz., varying ambient temperature, high frequency and amplitudes at higher wheel loads.

Seals Assembled on Floating Piston Assembly

The 110 mm diameter seal configuration has been indigenously designed and composition of seal constituents’ material identified to replace imported seals being used presently. So far three iteration of testing for 50 hours have been completed and further improvements on the performance of seals are being carried out.

Further high-temperature, high-pressure piston seals have been developed and tested with HSU on Arjun-PPS XII tank. The tank has undergone 5000 km trials so far without any failure. Based on the performance of the seals, clearance has been given

to Bharat Earth Movers Limited (BEML), Bengaluru, for fitment of the seals with production orders of HSU. Efforts have been made to arrive at the performance governing parameters by undertaking various tests and trials on a lot of samples picked up from the raw seal material, to use the results in the respective QAI document. Service order has been placed to M/s CIPET, Chennai, Ministry of Chemical and Fertilizer, Govt of India. CIPET has carried out the necessary tests and trials by using the samples provided by M/s Fluro Carbon Seals, Chennai. The trial data have been filled in the respective entry area of the QAI. Next batch of samples will be taken up for yet another set of test and trials to narrow down the uncertainty factors obtained from the previous tests.

Technologies for Transmission SystemsFluid Coupling and Retarder

CVRDE is developing a 1500 hp fully automatic hydrodynamic mechanical transmission system for AFVs. The system comprises various sub-systems, viz., speed change gearbox, direction change gearbox,

Figure 19. Sliding piston Figure 20. Floating piston

Figure 21. Sliding and floating pistons with assembly cylinders

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mechanical steering unit, steering differential, torque convertor, fluid coupling and retarder, etc.

Fluid coupling is a hydrodynamic coupling, which consists of two major bladed components, namely, impeller and turbine. Oil is used as power transmitting media from impeller to turbine. The fluid coupling system used in 1500 hp transmission can transmit 170 kW power. The rated speed of this unit is 6720 rpm and it is used for driving the cooling fan through a suitable gear train and control the speed of cooling fan in accordance with coolant temperature. Oil supply to fluid coupling varies according to coolant temperature, which results in change in slip as well as change in output speed.

Retarder is a hydrodynamic device used for decelerating the vehicle and running the vehicle at desired speed in downhill operation. Retarder and main brakes together provide high braking power to vehicle. Retarder also increases the life of main brake shoes by sharing its load. Both fluid coupling and retarder are assembled in a single casing and receive drive from a common shaft. Input to this assembly is from primary side of torque convertor through gear

Figure 22. Fluid coupling testing arrangement

drive. Fluid coupling and retarder are required to function independently and also together.

Three prototypes of fluid coupling and retarder assembly have been developed and tested in a separate test-rig especially designed and developed for testing of fluid coupling and retarder. Hydraulic circuit, having special oil inlet and outlet valves, has also been developed for supplying oil to both units at different flow rates. The hydraulic circuit employs standard pumps, filters, pressure relief valves, flow meters and solenoid valves for achieving the test requirements of the test rig. Speed, torque, power and temperature data have been recorded and analyzed for studying fluid coupling characteristic behaviour and power loss at different input speeds and slips.

Development and testing of fluid coupling and retarder running at more than 6000 rpm have been done first time in India. Compact fluid coupling and retarder for high power rating (170-225 kW) and high speed application (6700 rpm) is not available within India. CVRDE has successfully designed and developed prototypes and validated these successfully as an effort for indigenisation of technology.

Development of 1500 hp and 550 hp Torque Converters

The 1500 hp fully automatic hydrodynamic mechanical transmission system for AFVs is being developed. Torque converter used for torque multiplication is a major sub-system of this transmission. Other sub-systems of transmission are speed change gearbox, direction change gearbox, mechanical steering unit, steering differential, fluid coupling and retarder, final drive, etc. Torque converter is a hydrodynamic device consisting of three major

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bladed components, namely, impeller, stator and turbine. Impeller is connected with input drive (engine), turbine is connected to load (wheel or sprocket) and stator is coupled with a stationary casing through one way clutch. Stator is a reaction member and thus gives torque multiplication. After the coupling point the stator rotates along with impeller. Oil is used as power transmitting media from impeller to turbine. Torque converter multiplies torque to provide quick start, easy gradient climbing and high acceleration to vehicle. It makes gear-shifting smooth and absorbs jerks.

Two torque converters have been developed for 1500 hp and 550 hp transmissions. The single-stage, two-phase, three-element torque converters have stall torque ratio of 2.4. The 1500 hp torque converter is rated for a speed of 3000 revolution per minute. It operates in two phases｜torque converter mode and

lock-up mode. When required, torque converter can be bypassed through hydraulically actuated lock-up clutch. Converter mode is used for starting and during gear shifts for better fuel economy. The converter remains in lock-up mode during the remaining period.

Three prototypes of torque converters have been developed and tested for each power rating. A dedicated test-rig, a hydraulic circuit consisting of gear pumps, filters, pressure relief valves, pressure and temperature gauges and flow meters have been developed for achieving the test requirements of

Figure 23. Assembly of 1500 hp torque converter

the test rig. Input and output torque, inlet, outlet and lubrication flow rates, converter inlet and outlet temperature, coolant and sump temperature, input and output speeds, inlet and outlet pressure, lock-up and lubrication pressure were recorded using online data acquisition system to analyse the performance characteristics curves of torque converter at constant input speed of 2000 revolution per minute. The lock-up clutch torque transmitting capacity was also test evaluated for selected converter speeds and lock-up pressures and was found satisfactory. An endurance testing to demonstrate the lock-up clutch was carried out by continuously engaging and disengaging the clutches by running the converter at a particular speed ratio with the simulation of inertia. The converters stall torque capability was determined by locking the output shaft while running the converter at peak torque condition for three input speeds.

Design and development of torque converter was a critical area. As an effort for indigenisation of technologies, design of torque converter has been established including the bladed components for the first time in India.

Defensive Aids System for AFVsDefensive Aids System (DAS) enhances the

survivability of AFVs against modern sensors and Anti-tank Guided Missiles (ATGM) detection systems. CVRDE has developed indigenous DAS for AFVs. The system comprises a Mobile Camouflage System (MCS) and an Advanced Laser Warning and Countermeasure System (ALWCS).

Mobile Camouflage System The MCS provides multi-spectral signature

management for the AFVs to protect the vehicle against

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all sensors and smart munitions. The performance evaluation trials of MCS have been conducted at MFFR and system has been integrated in the Arjun MBT.

Advanced Laser Warning Countermeasure System

The ALWCS increases the survivability of the combat vehicle against ATGMs with Semi Automatic Command to Line-of-Sight (SACLOS) system, ATGMs with a laser target designator, beam rider ATGMs,

Figure 24. Mobile camouflage system

and tanks fitted with laser range finder. ALWCS has been integrated with Arjun MBT and interfaced with integrated fire control system (IFCS). The performance evaluation trials have been conducted at MFFR, Rajasthan. This system is a major value addition for Arjun MBT Mk-II.

Arjun MBT Troop Training SimulatorCVRDE has established a state-of-the-art Arjun

MBT simulator training centre, the first of its kind in India, for AFV crew training. Three driving simulators and three turret simulators have been indigenously developed and installed. The simulators are configured to provide individual crew-level technical training to integrated tank- and troop-level tactical training. This innovative training facility caters for safer, cost-effective and round-the-clock training to the Arjun MBT crew without using Figure 25. Advanced laser warning countermeasure system

Figure 26. Smoke grenade discharged from the tank

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the actual tank and ammunition. This saves enormous expenditure required for training the newly recruited Army crew.

The crew gets familiarised on various technical and tactical drills in the simulator with awareness to handle emergencies during training, which is not possible through actual tank. This enhances the performance of the crew so that the actual tank can be handled effectively and hence its fighting capability can be explored to the maximum possible extent. Instructor station monitors and controls the actions of nine crew members during troop training. Online evaluation with appropriate ranking and after action review is provided at the instructor station to assess the strength and weakness of the crew during training. This indigenous effort has enhanced self-reliance in the area of AFV crew training requirements of Indian Army.

Turret Simulator

Turret simulator com-prises replicated Arjun MBT turret compartment hard-ware controls with day and night visions for gunner, and panoramic and episcope vision for commander to handle the battle conditions effectively. The turret simu-lator helps to familiarise the gunner and commander on various functions and

operational procedure to be followed in the turret compartment to engage and fire on the targets.

Salient FeaturesCommander’s override operations and surveillance aprocedures training

Identification and prioritisation of targets with abattlefield lessons

Navigation training through global positioning asystem

Target engagement, tracking, laying and firing apractices with main gun and machine gun

Training under different terrain, environment and avisibility conditions

Figure 27. Internal view of Commander's and Gunner's compartment

Figure 28. Instruction station with consoles and turret cabin on motion system

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Figure 29. L-R: Driver compartment internal view (front side); hatch open driving simulation and driver's cabin on motion system

and visibility conditions with emergencies and obstacles

Gear selection for different driving conditions a

Fording exercises with underwater effects a

Lessons for hatch open and hatch closed driving a

Collision effects and its synchronisation with motion acues during driving

Instructor console to plan, monitor the driver actions aand evaluate him with ranking

Troop Training Simulator

Troop training simulators for MBTs are available in various countries across the world. However, in India this is the first troop training simulator developed indigenously for Arjun MBT to train three gunners, three commanders and three drivers together in a simulated tactical mission plan environment. To meet this tactical training three turret simulators and three driving simulators were interconnected through high speed LAN.

Each turret and driving simulators are mounted on a 6 DOF electrical motion system to generate realistic motion cues and disturbances experienced by the crew inside the MBT. Six such motion systems were commissioned in an air-conditioned high roof bay for

Firing with explosion, dust, smoke and recoil aeffects

Instructor console to plan, monitor the Gunner's aand Commander's actions and evaluates these with ranking

Driving SimulatorThe driving simulator helps the driver to get

familiarised on various hardware controls and switches present in the compartment and operational procedures to be followed while driving the tank. The driving simulator is provided with actual driver compartment hardware controls with periscope vision for day time driving and Passive Night Vision Devices (PNVD) for night time driving. This simulator cabin is mounted on 6 DOF (degree of freedom) electrical motion systems to provide the realistic roll, pitch, and yaw feel to the driver. The hatch open driving simulation provides with battlefield sceneries projected on cylindrical screen to cover 200° horizontal FOV and 45° vertical FOV. This helps the driver to get immersed under virtual reality based motion, aural and visual cues synchronisation.

Salient Features

Lesson plans for the driver to prepare the vehicle aunder different start up and stopping conditions

Driving practice on different terrain, time, seasons a

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Open hatch display system for driver with 200° (H) a

and 45° (V) FOV

PNVD and thermal imager for the crew during night atime operations

Camera view to monitor the physical movement of anine crew and six motion systems during simulator operation

troop training. Real-time response based on the nine crew members actions during troop training have been achieved realistically by synchronising six motion cues, 36 visual cues and various aural cues in the simulator.

Salient Features Lesson plan to cater tactical training with atroop formation procedures

Scenario editing with proper mission plans for aeach tank

Plan, monitor and control the crew actions athrough instructor console

Record and replay the crew actions during atraining

Monitoring of nine crew actions through single ainstructor station during troop training

Communication among nine crew members and ainstructor

Emergency controls for six motion systems a

Training under different terrain and environmental aconditions

Technology Focus focuses on the technological developments in the Organisation, covering the products, processes and technologies.

Figure 30. Three turret and driving simulators