SKfz 303
General Characteristics:
- Type: Armored ambulance
- Weight: 31.0 t
- Length: 6.8 m
- Width: 3.4 m
- Height: 2.4 m
- Crew: 3 (driver, commander, medic) + 6 ambulatory patients
Mobility:
- Engine: 2x AMG HL44 multi-fuel twin-turbo V4 diesel engines, 400 kW (550 PS) each
- Transmission: Diesel-electric; 2x 300 kW traction motors, 2x 150 kW steering motors
- Suspension: Active in-arm hydropneumatic
- Max onroad speed: 75 km/h
- Max offroad speed: 60 km/h
- Max reverse speed: 30 km/h
- Fuel capacity: 950 l
- Operational range: 750 km
Maneuverability:
- Power/weight Ratio: 37.0 PS/t (26.7 kW/t)
- Ground clearance: 0.50 m
- Ground pressure: 0.70 kg/cm2
- Gradient: 60%
- Sideslope: 40%
- Fording depth: 1.5 m
- Trench crossing: 2.6 m
- Vertical wall climb: 1.0 m
Overview
The Sanitätskraftfahrzeug 303 (SKfz 303) is an armored ambulance designed by SDI vehicle systems. The vehicle is a variant of SDI's PzBfw 303 command vehicle and consists of a PzBfw 303 modified to function as an emergency medical treatment and evacuationvehicle for personnel wounded or injured on the battlefield.
Protection:Armor Protection: The hull of the vehicle is constructed from friction stir welded (FSW) 2139-T8 aluminum alloy plates 40 mm thick which provides the hull 360° protection against 14.5 mm AP ammunition at 200 meters and 155 mm high explosive shell fragments at 30 meters. The inside surface of the vehicle features a borated spall liner consisting of orthogonally cross-plied M5 ballistic fibers laminated into a flexible borated polyethylene resin which serves to minimize the post-armor effect of penetrating projectiles and shaped charge jets and to provide radiation protection for the crew and electronics inside the vehicle. Under-belly protection is provided by an armored V-hull which provides protection against EFPs and 10kg TNT equivalent blast anti-tank mines. Additionally the four vehicle crew members located in the hull sit on blast-attenuating seats with no direct contact to the vehicle floor.
Fire extinguishing system: The crew, fuel, and powertrain compartments of the vehicle include an automatic fire suppression system (AFSS) which is designed to prevent fires inside the vehicle caused by penetrating munitions. Combined UV/IR electro-optical infrared sensors placed inside the crew and ammunition compartments and are used to detect the formation of explosive fires inside the vehicle within several milliseconds. The engine, transmission, and fuel compartments of the vehicle substitute the electro-optical sensors with several loop of thermal sensing wire. When a fire is detected inside the vehicle Halon 1301 contained in several pressurized bottles each with fast-reacting solenoid-actuated valves is sprayed into the compartment to extinguish the fire. After the compartment is flooded with halon and the fire extinguished the vehicle's ventilator is automatically switched on and the residual smoke and halon gas is then vented to the atmosphere.
NBC System: The vehicle's NBC systems consists of pressure swing adsorption (PSA) system which supplied filtered air to the crew compartment and maintains fighting compartment pressure at a constant 4 millibar above outside atmospheric pressure. The pressure swing adsorption (PSA) system works by using two filter beds' one adsorbing at high pressure while the other is regenerating at low pressure by the removal of previously adsorbed particles. Following regeneration the incoming air is diverted to the cleaned bed and the bed previously on line begins its regeneration cycle. Air first is drawn into the system through a cyclone filter which removes dust and biological particles from the air before it enters the first stage air compressor. The first stage air compressor raises the air pressure to 1.8 bar where the air is then cooled by passing through the first stage heat exchanger before it enters the second stage air compressor. The second stage air compressor raises the air pressure to 3.0 bar where the air is again cooled by passing it through the second stage heat exchanger. The air then enters the on-line bed where it is cleaned . The cleaned air that leaves the on-line bed is cooled by passing it through a recuperator where it is then expanded through a turbine which drives the second stage air compressor. The cold air leaving the turbine is released into the crew compartment through a pressure relief valve (PRV) which maintains the crew compartment at 4 millibar above outside atmospheric pressure.
PropulsionThe vehicle employs a diesel-electric drive system consisting of twin diesel engines and integrated starer/generator units places in the hull sponsons and a mechanically regenerated hybrid electro-mechanical cross-drive transmission located in the front of the hull which combines the power input of the traction and steering motors and distributes it to the twin drive sprockets. The mechanical decoupling of the diesel engines with the drive sprockets allows for the engines to run at a constant RPM, improving fuel efficiency, while the use of two diesel propulsion units and twin steering and traction motors in the transmission provides a high level of redundancy and resistance to damage. The packaging of the diesel engines in the hull sponsons also serve to increase the effective internal volume of the hull for crew, weapons, and other payload.
- Name: HL44
- Type: Multi-fuel diesel engine
- Length: 890 mm
- Width: 450 mm
- Height: 740 mm
- Dry Weight: 450 kg
- Bore/stroke: 115/105 mm
- Displacement, cylinder: 1.1 l
- Displacement, total: 4.4l
- Charging method: two-stage variable-geometry turbocharger
- Intercooling: Air-oil aftercooler
- Number of Cylinders: 4, inline
- Cooling method: Water cooled
- Injection method: Common rail, piezoelectric direct injection
- Specific fuel consumption: 190 g/kW-hr
- Power: 400 kW @ 4,300 RPM
- Torque: 920 N-m @ 3,800 RPM
- Fuel: JP-5, JP-8, Ultra-low sulfur diesel
Engine: The engine used in each powerpack is an AMG (Arkaenisch Motorenfabrik Gesellschaft) HL44, a four cylinder inline, common rail fuel fuel injection, twin sequentially charged low-heat rejection diesel engine which outputs a maximum 400 kW of power at 4,300 rpm. The engine also includes an integral oil-cooled permanent magnet synchronous flywheel starter-generator unit which is geared to the engine output shaft using a speed-increasing transfer case with a fixed 4.2:1 gear ratio. The HL44 employs a common rail fuel-injection system with a fuel rail running the length of the engine and twin hydraulic boost pumps running at up to 3,100 rpm to pressurize the fuel to 1,800 bar for injection into each cylinder. Turbocharging is accomplished with twin single-stage variable-geometry turbocharger units using variable-area turbine nozzles which providing boost pressure ratios up to 5:1. A water-to-air charge-air cooler is placed after the turbocharger compressor stages to cool and density the air before entering the combustion chambers. To maximize engine performance across a broad ambient temperature spectrum the water and oil cooling system of the engine are split into a high temperature loop which cools the piston liners, cylinder heads, and other engine components along with the first stage of the charge-air cooler, and a low temperature loop which cools the power electronics, engine oil, and the second stage of the charge-air cooler. A dual-circuit water pump circulates cooling water through both the high and low temperature loops and then through the radiator cooling system which employs twin 30 kilowatt variable-speed fans to cool the coolant before it's passed into the expansion tank and then circulated again through the twin coolant loops. An integrated flywheel starter generator is used to start the engine and is rated for mechanical input power of up to 400 kW and outputs 3 phase 60 Hz 600 VAC alternating current The starter-generator is a self-excited, brushless, oil cooled, permanent magnet machine using neodymium-iron-boron permanent magnets and has a rated speed of 18,000 RPM, necessitating a 4.2:1 gear ratio speed-increaser gearbox be placed between the generator and engine. Other engine accessories including inlet air filter system, turbo intercooler and aftercooler circuits, charge air cooler with inlet manifold, exhaust scrubber and infrared suppression system, and oil filter and cooler, are included in the power pack as a single engine unit. The left and right hand side powerpacks are identical and can be fitted to either side of the vehicle. The powerpack additionally includes the oil cooling system with air-oil heat exchanger and a hydrostatically driven cooling fan.
Transmission: The vehicle powertrain system employs a mechanically regenerated cross-drive transmission which reduces the required motor power required to drive and regeneratively brake each drive sprocket. The transmission system includes twin 150 kilowatt oil-cooled permanent magnet synchronous steering motors and twin 300 kilowatt oil-cooled permanent magnet synchronous traction motors located on either sides of the transmission. Both traction and steering motors employ a rotor with samarium-cobalt magnets and a ferromagnetic core with an inconel superalloy sleeve and have a maximum rated speed of 18,500 RPM with a 93% efficiency at a base speed of 4,600 RPM. The steering and traction motors on either side of the transmission are supplied electrical power through a generator converter box located in each sponson ahead of the the powerpack which converts the three phase 600 volt AC power from the engine generators into 600 volt DC power which is transferred to a DC bus located on either side of the cross drive unit which then supplies DC power to the motor inverters and the various accessory drives. The cross drive unit itself contains a central drive shaft connected to a differential gearbox which combines the inputs from the two steering motors and two traction motors to power the drive sprockets through the planetary reduction final drive assemblies located on either side of the cross-drive transmission. A two speed oil-cooled planetary reduction gearbox with twin hydraulically actuated clutches is additionally incorporated into the cross-drive transmission and connects the central differential to the steering and traction motors to reduce the required rpm and torque ranges of the electrical steering and traction motors. The cross drive additionally contains an oil cooled wet disk brake and a parking brake unit.
Suspension & Running Gear: The suspension system used by the vehicle is an SDI designed semi-active in-arm hydro-pneumatic suspension system with three sets of paired, overlapping 800 mm diameter rubber-tired road wheels on either side of the chassis (12 road wheels total) each mounted on a swing-arm with an integral in-arm suspension unit (ISU) which allows for independent control of each road wheel bogie. Each ISU consists of a compressed nitrogen shock absorber and hydraulic dampener unit contained inside the roadwheel arm. When the arm rotates upward a piston-arm attached to a stationary pivot is forced into a cylinder in the moving suspension arm which in turn displaces the hydraulic fuel inside and compresses the nitrogen gas inside, causing the unit to act as a spring. The variable damping of the suspension is provided by a stack of hydro-mechanically controlled wet friction discs located on the hull pivot axis of the in arm suspension unit which are compressed by a hydraulic pressure plate to vary the dampening rate of the suspension arm as a function of the suspension arm position and velocity. Ground clearance of the vehicle is adjustable by the driver from between 100 and 700 mm, depending on terrain. The vehicle's running gear features a decoupled design where the final drives and sprockets, idlers, and roadwheel arms are all mounted on left and right side running gear carriers which are decoupled from the sides of the hull using rubber mounts. The vehicle's road wheels employ a twin hollow shell design formed using twin hollow cavities constructed from a single 7075-T6 aluminum alloy forging fitted with an inner steel wear ring and polyurethane tire which are then bolted together back-to-back to form the complete road wheel units. Instead of conventional steel tracks the vehicle employs composite rubber band tracks which are 50% lighter and result in a 70% vibration reduction and 10 dB noise reduction inside the vehicle at a road speed of 50 kph. The tracks are 550 mm wide with a 120 mm pitch and have a designed durability of over 5,000 km before needing replacing.
Variants:SKfz 303: Ambulance and medical treatment vehicle which can be configured either as an ambulance or medical treatment vehicle. As an ambulance the vehicle has a crew of 3 and can carry 6 ambulatory patients, 4 litter patients, or 3 ambulatory patients and 2 litter patients. As a medical treatment vehicle the vehicle has a crew of 4 with the ability to carry 1 litter patient and includes an erectable treatment shelter, various medical equipment including vital signs monitor and defibrillators, and a refrigerator for storing blood.
