Forza Boxer 6 Cylinder Twincharged (Supercharged - Turbocharged) Diesel Hybrid Engine - FB-6TSDH
The FB-6TSDH engine is a diesel-electric hybrid six-cylinder boxer engine displacing only a mere 9.2 Litres yet producing nearly 500kw of power employing the Internal Comustion Engine only, and over 700kw with electric power boost. The hybrid system, Forza's own HybriDrive technology, not only ensures that the vehicle is one of, if not the, most powerful, fastest and fastest accelerating IFVs in it's class, but, when teamed small displacement internal combustion engine, also makes it one of the most fuel efficient armoured fighting vehicles ever produced.
The main reason for the immense power output of the Forza FB-6TSDH engine is the teaming of it's high-boost forced induction system along with it's very high compression ratio. For a direct commonrail injected diesel engine, this version of the FB-HTSD posseses a ratio of 23.5:1, essentially meaning the engine compresses 1540 cubic centimetres of fuel and air mixture into 63 cubic centimetres in every cycle. The compression ratio is acheived by long stroke of the existing FB-6TSDH powerplant. Because of this very high ratio, this called for the cylinder block to be manufactured with very thick cylinder walls in order to maintain it's structural integrity. Despite it's low displacement, the FB-6TSDH weighs no less than a similarly powerful 20 litre engine when one factors in the additional weight of the HybriDrive system, although consuming much less fuel.
To further boost power, the maximum boost of the turbochargers was set 1.6 bar, which creates a significant increase in power when the turbochargers are active higher up the rev range, but due to the nature of a twincharger engine, makes no difference in low engine speeds due to the supercharger being the sole provider of forced induction.
Forza engineers designed the FB-6TSDH as a six cylinder boxer, although a twelve cylinder was the preferred choice by the Anago-Yohannesian Kaissereich, simply because it allowed more space for the HybriDrive system to be fitted. The risk of a cylinder failing was more or less written off as a risk due to the presence of the battery pack and electric motors which could propel the vehicle to safety in case the worst came to the worst.
The pistons are arranged in a boxer layout which is a layout seldom seen except for several high performance sports cars. A flat layout, which is more commonly seen, is near identical in appearence and theory to a boxer engine; there is still a 180 degree angle between the two seperate banks of pistons, however a boxer engine mounts two opposing pistons on two different crank pins as opposed to a flat engine which mounts two pistons on the same crank pin.
Thus, a flat layout is best described as a 180 degree V engine and not a true boxer engine. Boxer engines are reknown for having superb balance and are unique in that a boxer engine does not require counter balances at all on the crank shaft as the engine has superb natural balance. This is further enhanced by the use of twelve cylinders. Boxers are so named because when one looks at the engine from down the crankshaft, the two banks of cylinders will appear to be boxing one another.
The induction system is a variant of Forza's TwinCharger system; a single Roots-type Superchager is used to aspirate the engine at low RPM's with two Turbochargers, one for each bank of cylinders, aspirating the engine further down the rev-range. TwinCharging systems have a number of advantages over other forms of forced induction. Unlike Turbocharged engines, Twincharged engines do not experience turbo-lag, where the turbochargers are ineffective because they are not at operating speeds.
Unlike supercharged engines, twincharged engines can decouple the supercharger from the engine so that it won't drain power to operate while still maintaining boost from the turbochargers. The two forms of forced induction do not operate in parallel in a bid to avoid the extremely high manifold temperatures which would be produced by the supercharger blowing into the turbocharger. As such, the supercharger is decoupled as soon as the turbocharger activates on the FB-6TSDH. The TwinCharger system alone allows the vehicle to have constant boost and thus give exceptional acceleration at all engine speeds; something crucial for a battlefield environment.
The engine block itself is made from aluminium alloy, comprised of 11% silicon, 4% manganese and 0.5% magnesium. This Al-Alloy has a high thermal conductivity and hence is able to dissipate heat quicker than cast iron. Also, it leads more thermal efficiency, cooler running engines and are lighter thereby improving the overall vehicle’s operative characteristics.
In total, the engine has a total displacement of 9,240 cubic centimetres or 9.24 Litres, which equates to 1.54 Litres per cylinder. This version of the FB-6TSDH, with its high compression ratio and boost pressure creates a specific output of 54kw/litre, which combines to form a total output of 499kw. This is only the power of the internal combustion engine.
Exhaust fumes and gases are passed out the rear of the tank, through a double muffler and particle filter. Exhaust gases are diluted with outside air to reduce their heat signature. This is done by sucking air through a small inlet flush against the tank and mixing the cool outside air with the exhaust gases. Exhausted and outside air meet in a special Y tube, with a radiator being mounted on the stem of the Y, sucking air from both stems through to the exhaust.
Sound-deadening engine covers are also fitted to the engine to reduce the noise both inside and outside the cabin. Forza engineers are normally ardent at reducing the NVH of large luxury cars but found the same basic principles applied to armoured vehicles. Double-insulated sound covers are placed in a box to cover the engine, which is itself mounted on springs to quell vibrations. The top of this box can be easily removed to lift the whole engine out. As a result, the vehicle, similar to the AY1 MBT, is drastically quieter inside and out than the majority of most if not all other infantry fighting vehicles.
The Forza HybriDrive replaces a normal geared transmission with an electromechanical system. Because an internal combustion engine (ICE) delivers power best only over a small range of torques and speeds, the crankshaft of the engine is usually attached to an automatic or manual transmission by a clutch or torque converter that allows the driver to adjust the speed and torque that can be delivered by the engine to the torque and speed needed to drive the wheels of the car. For classification purposes, the gearbox can be described as an Electronic Continuously Variable Transmission, or EVT.
The HybriDrive system replaces the gearbox, alternator and starter motor with a three-phase brushless alternator serving as a generator, two powerful motor-generators, a computerized shunt system to control the afforementioned devices, a mechanical power splitter that acts as a second differential, and a battery pack that serves as an energy reservoir. The motor-generator uses power from the battery pack to propel the vehicle at startup and at low speeds or under acceleration. The ICE may or may not be running at startup. When higher speeds, faster acceleration or more power for charging the batteries is needed the ICE is started by the motor-generator, acting as a starter motor.
When the operator wants the vehicle to slow down the initial travel of the brake pedal engages the motor-generator into generator mode converting much of the forward motion into electrical current flow which is used to recharge the batteries while slowing down the vehicle. In this way the forward momentum regenerates or converts much of the energy used to accelerate the vehicle back into stored electrical energy.
The sole purpose of the brushless alternator is to convert mechanical energy generated by the ICE and convert it into electrical energy which is stored in the battery pack. In addition, by regulating the amount of electrical power generated, the alternator also controls and regulates the transmission of the vehicle by changing the internal resistance of the alternator. The pair of motor generators drive the vehicle in tandem with the ICE. The two roles are not interchangeable. When the two motor generators are in operation, they create an extra 200kw of between them.
The mechanical gearing design of the system allows the mechanical power from the ICE to be split three ways: extra torque, extra rotation speed, and power for an electric generator. A computer program running appropriate actuators controls the systems and directs the power flow from the different engine and the electric motor sources. This power split achieves the benefits of a continuously variable transmission (CVT), except that the torque/speed conversion uses an electric motor rather than a direct mechanical gear train connection. The vehicle cannot operate without the computer, power electronics, battery pack and motor-generators, though in principle it could operate while missing the internal combustion engine.
The transmission contains a planetary gear set that adjusts and blends the amount of torque from the engine and motors as it’s needed. Special couplings and sensors monitor rotation speed of each track and the total torque on the tracks, for feedback to the control computer.
In summary, the HybriDrive system works by the brushless alternator feeding electric power to the battery pack where it is stored, before it is supplied to the two motor generators which rectify the electric energy into mechanical energy, where it is then used to drive the tracks. Furthermore, during normal operation the engine can be operated at or near its ideal speed and torque level for power, economy, or emissions, with the battery pack absorbing or supplying power as appropriate to balance the demand placed by the driver. During stoppages the internal combustion engine can even be turned off for even more economy.
Two other advantages are made possible by this set up.
The first is "Stealth Mode," where the vehicle can travel at slow to medium speeds without using the ICE for power, thus running silently. This gives an assaulting force an enourmous advantage as an enemy will generally not be able to hear the IFV approaching, except over rough ground which would cause noise. However, the absence of an engine note will mean that the noise of the tracks on the ground alone will not alert the enemy to the presence of an IFV. In this mode, the alternator spins freely and the engine is de-coupled from the rest of the drivetrain. Stealth Mode can be run for up to fourty minutes or fifty kilometres running off the battery power. After this, the ICE will need to recharge the battery pack.
The second is the "Overboost" function. When accelerating, the vehicle teams the powerful ICE with the pair of motor-generators to combine their power and torque, resulting in a huge boost to acceleration. The Overboost function can also be employed for the vehicle to act as a tug, by either pushing or pulling an otherwise immobile vehicle, up to an eighty tonne MBT, to a safer position.
The vehicle is able to reach comparitively high speeds for a tracked vehicle by the use of protective rubber covers placed over the steel tracks. Effectively, these covers are essentially odd sized tyres which cannot be inflated. The outside of these rubber tracks are made from dense and durable rubber while the inner of the covering track is made from high-density latex which provides a limited shock absorbtion role, thus greatly reducing the stress placed upon the steel tracks underneath the rubber covering. If this exterior cover is damaged, it can be easily shed from the track and the track can continue on it's way relatively unaffected aside from a much lower maximum speed.