Electric Drives for Combat Vehicles
Sub Title : Modernisation of combat vehicles and future designs should include electric drives
Issues Details : Vol 17 Issue 3 Jul – Aug 2023
Author : Lt Gen N B Singh (retd)
Page No. : 32
Category : Military Technology
: August 2, 2023
Militaries world over are looking at going electric in order to go green and also improve combat effectiveness. The move makes sense from all angles; enhancing stealth and lethality of platforms, fuel saving and higher efficiency
Most militaries in the 21st century are focussing on weaponization of new technologies with the aim of achieving an operational overreach over the opponent. Present day combat vehicles are packed with sensors and devices that consume a lot of power. Consequently power management is becoming an area of interest in the development of future combat systems. Integrating a Electric Drives into combat vehicles could vastly increase availability of on-board power, enhance physical agility and lethality and extend operational range. With the impressive development in commercial electric vehicle technologies, combat vehicles(CV) can derive a number of advantages like enhancement of fuel economy, acceleration, hill climbing ability, silent watch, etc.
Electric drives have been experimented by a no of countries since early 20th century. The Saint-Chamond tank was built in between 1916 and 1918 in France and deployed in the First World War. Germany built and deployed Ferdinand tank in the Second World War. The US developed T23 tank with an electric drive in 1943 and evaluated its performance. However, these pioneering efforts could not be taken forward due to the immaturity of relevant technologies. In the mid eighties attempts were again made to analyse electric drives by developing a 40 ton tank and an 18 ton APC drive. Since 2020, interest in electric drives has been revived seeing the remarkable progress made in electric vehicles(EV).
Going Green- An Indispensable Option for the Military
Russian logistics failures and images of 60 km long convoys that had got grounded in and around Kiev indicates how difficult it is to refuel combat vehicles in the stride. An armoured division could use up to 1000 kilo litres of fuel a day. Moving such large amounts of fuel in the battle area securely to forward replenishment points is becoming increasingly difficult for the fuel logistician. On the other hand the employment of silent electric bikes by Ukrainian sharp shooters demonstrates how electric drives and such technologies can enhance combat effectiveness.
To be able to maintain the tempo of operations it makes sense to switch over to electric drives to reduce the quantum of fuel replenishment. Coupled to it is the pressing need to cut down emissions that are increasing causing an unbalance in the environment. The US military is making the initial moves towards electric drives. There are some programmes that have been initiated to evaluate the technologies and operational benefits. The Abrams X Tank project is aiming to reduce weight, by going in for a smaller and lighter engine covering most duty cycles. Stryker X Hybrid project is looking at a drive to achieve higher speeds, cover longer distances on battery power and silent watch.
BAE systems has offered 2x Bradley vehicles with hybrid drives for testing and evaluation. The system is scalable to fit vehicles from 30 to 60 tonnes. GM has offered the Ultium platform with scalable packs from 50 KWh to 200 KWh. A Hummer electric vehicle is also reportedly under trial. Oshkosh Defense has created a fuel efficient electric Joint Light Tactical Vehicle (eJLTV). US Army has concluded that electrification of combat vehicles is very much desirable; however the overall consensus seems to be that hybrid electric drive (HED) is what is feasible today.
In France, Nexter is working with Arquus and Texelis on several HED vehicles for the Scorpion Programme: Griffon 6×6 and Serval 4×4, both multi-role armoured vehicles. UK Armed Forces have started testing three different HED vehicles under mission-relevant conditions as part of the Technology Demonstrator 6 Programme. Other programmes like the Jackal 2, 4×4, a highly mobile patrol vehicle, the Foxhound 4×4, a protected patrol vehicle and MAN HX60 4×4, a tactical truck are other initiatives under evaluation.
Types of Electric Drives
Basically there are three types of electric drives; the full electric where an IC engine runs an alternator that powers electric motors located at the wheels or sprockets. The second one is the hybrid electric drive (HED) where mechanical and electric power provided by an IC engine and a battery pack are available at the wheels or tracks. The third type of drive is all battery like the one being used in Tesla. The last type, that is full battery drive is still far off for CVs due to recharging infrastructure requirements in the combat zone and lower capacities in sub zero temperatures. The energy density of batteries today is inadequate and results in excessive battery pack weight and volume to meet manoeuvre requirements. Besides, recharging of all-electric vehicles during tactical pauses would require massive quantities of electric power. A station charging several vehicles could be a lucrative target for battlefield interdiction. There are numerous operational advantages in terms of torque, acceleration and fuel efficiency, but the prospects favour either HED or IC engine – electric drive (ICED) seeing the current state of EV technology.
Batteries are a critical component and they are overwhelmingly on lithium, cobalt and other raw materials that are largely sourced from abroad. This creates a weak and brittle supply chain. The discovery of lithium deposits in Jammu and Rajasthan is timely. It should provide the necessary fillip to indigenous EV manufacturing. A significant loss in energy and power densities at low temperatures limits use of lithium-ion batteries at sub-zero temperatures. There is work in progress to develop 6-8 other types of batteries that could reduce costs and improve low temperature performance. Battery volatility and transport safety is another risk. Costs of lithium ion battery pack has come down from $1100 to $150 per kWh in a decade.
Operational Advantages of Electric Drives
With widespread digitisation of platforms, on-board electricity demand will continue to increase in future due to energy-hungry systems: software defined radios, IED jammers, battle management systems, radars, cameras, remote-controlled weapon, charging docks for drones, laser weapons, etc. HED architectures can not only meet these energy needs but can also be used flexibly as mobile generators for local power grids. For AFVs it could conserve engine life by enabling silent watch using battery pack. Due to reduction of the size of engine compartment, it may be feasible to store more ammunition.
In our context of operations in mountains, high altitude and deserts, electric drives offer several significant operational advantages. Higher acceleration improves physical agility of the platform. Since EV is driven by electric motors, the acceleration is smoother and pick up more powerful than vehicles with mechanical drive. It can climb slopes of 60% even at very low speed (around 5 kilo meter per hour) owing to the large torque at low speed of the motor and make a pivot turn with mechanically decoupled motors.
Full Electric Drives
Fig 2 gives the layout of a pure battery electric drive. The biggest limitation for CV electrification will be the lower power to weight ratio. As a rough estimate, 4 litres of petrol weighs 3 kgs and generates 33.7 kWh of energy, whereas a 33.7kWh battery pack weighs 216 kg @ 6.4 kg per kWh. So its incorporation may not be operationally feasible till technology matures and mobile grids feasible. Powering an armoured brigade will need huge amount of power to recharge batteries eg a fleet of 6x Tatra EVs with 300 kWh battery, can get refuelled in 15 mins (engine version). These will need a 7 MW charging system and 45 mins at least to recharge. When compared with the size of Army`s 11.5 KW battery charger, one can visualise the enormity of the problem. There are moves to develop mobile nuclear power plants to charge EVs in battle. Hence for the time being full electric drives could be restricted to specialist vehicles like stackers, cranes, etc. Special forces could possibly look at recce vehicles providing stealth capabilities.
Fig 2 Pure Electric Drive
Hybrid Electric Drive
Fig 3 gives the general configuration of a HED for a wheeled vehicle. The wheels receive mechanical power from the IC engine as well electric motor. The torque augmentation of the motor at low speeds will enhance operational moves during low speeds in mountains and deserts. An onboard charger can meet the power requirements for all devices carried by recce and surveillance teams.
HED reduce noise and heat signature enabling silent watch. Furthermore, the performance of the vehicle can be optimised with each wheel controlled and driven individually by using hub motors and drive-by-wire technology. Depending on how the hybrid architecture connects the combustion engine and the electric motor in parallel or series, it can significantly increase engine power for a short time to give a burst mode for negotiating steep gradients in mountains and deserts. Separate drive trains increases the reliability of the overall system through redundancy. HEDs can mitigate low temperature performance of battery pack by managing battery temperature and state of charge.
Hybrid-electric architectures for tactical systems are expected to yield major operational advantages. HED could reduce fuel consumption by as much as 35 percent. Other advantages include silent watch and silent move, large range of operations, reduced thermal and acoustic signature, increased onboard power for sub systems like radars, sensors, jammers, active protection, particle beam weapons, reduced maintenance costs and logistics footprint.
There is a huge amount of activity in the Indian automobile sector to develop EVs. Under the EV30@30 global initiative India is looking at 30% share of EVs in the total sales of automobiles by 2030. The FAME (faster adoption and manufacture of EVs) initiative is aiming to localise all essential systems of EVs. It is time the Indian military looks at this technology both from zero emission and operational advantages angle and initiates programmes on indigenous electric and hybrid electric vehicles. A well conceived programme to achieve self reliance in military grade electric drives is crucial to support programmes like light tank, FICV, wheeled APC.
Next in line could be the hybridization of logistics vehicles and wheeled CVs. Projects to incubate military grade drives for tracked and wheeled CVs need to be initiated using the IDEX and technology development route to make India a hub of EV technology. India could replicate the German example of being a knowledge leader for mil grade IC engine based mobility systems, in the EV sphere. Fuel savings and export earnings will more than compensate for R&D and acquisition costs. Operational benefits to the war fighter will range from lighting, charging devices, better situational awareness, increased agility and lethality, silent operation, less maintenance and greater efficiency.
HED–An Effective Solution to T 72 Repowering
The Army has been attempting to repower the T72 with a 1000 hp modern engine to meet the mobility and power requirements for the past two decades. The adoption of HED could be considered as technologies exist today to bring this concept to fruition in a short time frame. Figure 3 gives the proposed power train with two traction motors driving the sprockets.
Fig 4: Tracked HED
It will employ regenerative braking as well as regenerative steering, allowing pivot turns, excellent gradeability and high acceleration, enhancing physical agility of the tank, improving survivability. It would greatly enhance mobility of tanks in HAA where it gives the tank independence from power losses due to increasing altitudes. Once the HED configuration is stabilised, it can be further optimised and space used to separate ammunition from crew, a major vulnerability of the tank. The HED can be designed as a scalable pack to meet all foreseeable power requirements for tracked CVs in the Indian context. The compactness of the HED will obviate the need to carry any cutting and welding of the hull during retro fitment.
Militaries world over are looking at going electric in order to go green and also improve combat effectiveness. The move makes sense from all angles; enhancing stealth and lethality of platforms, fuel saving and higher efficiency. In a typical IC engine around 16% to 25% power is delivered to the wheels whereas in case of electric drives this could be 85 to 90% if the gains of regenerative braking is taken into account. Battery costs are high today but it is expected that these will drastically come down by 2030 enabling replacement of most IC engines in civilian applications. Time for the military to be a part of this disruptive moment and pursue self reliance in combat EVs.