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FORD ECOSTAR

Battery/fuel-cell EV design packages

5.6 Electric van and truck design

5.6.5 FORD ECOSTAR

An electric vehicle with equivalent performance to an IC-engined one, and yet based on a conventional Escort van platform, Fig. 5.23, has been achieved by Ford with the use of a sodium–

sulphur battery. The battery is enclosed in a hermetically sealed metal casing, which contains sodium and sulphur on each side of a porous ceramic separator. In order to react on a molecular level, the sodium and sulphur must be free to flow through the separator in liquid form. This requires maintaining an operating temperature of between 290 and 350° C. The Ecostar’s battery pack is formed of a double-skinned, stainless steel case, with a glass fibre insulated cavity which has been evacuated to form a vacuum flask. Inside the case, 480 individual sodium–sulphur cells are embedded in a sand matrix to prevent movement and contain the elements in the event of a severe impact.

Each cell is encased in a corrosion-resistant aluminium cylinder and produces about 2 volts.

They are linked to provide a 330 volt power supply and a steady-load current of 80 amps. Power of up to 50 kW is available for short periods. The battery pack is mounted under the vehicle floor, ahead of the rear axle. The vehicle is fitted with an intelligent on-board charging system that automatically adjusts to the supply voltage from the mains. It can be used for overnight recharging and temperature control of the sodium–sulphur battery. A full recharge takes between 5 and 7 hours. In the event of electrical malfunction, the battery pack is isolated by replacing external 200 amp fuses at the battery connection box. The batteries are also equipped with internal fuses that isolate the electrical supply from the vehicle if there is any kind of internal overload.

The Ecostar, Fig. 5.21, is powered by a high speed, 3 phase alternating current (AC) motor, rated at 56 kW (75 bhp). It is directly coupled to the transaxle by a single-speed planetary reduction gear set. The motor operates at 330 volts, provided by the sodium–sulphur battery pack. Compared to equivalent DC systems, the AC motor works at a higher rate of efficiency, is smaller, lighter, lower in cost, easier to cool, more reliable and generally more durable. Maximum speed is 13 500

rpm and maximum torque 193 Nm at zero rpm. Regenerative braking comes from the motor acting as a generator, so recharging the battery.

The supply from the sodium–sulphur battery is fed along special heavy-duty cables to the power electronics centre (PEC), which is housed in the engine compartment. The candy-striped, red-on-black cables are strikingly marked to avoid confusion with any other wiring in the van. Encased in aluminium, the PEC incorporates the battery charging electronics and inverters that convert the 330 volt DC supply to AC power. It also includes a transformer which enables a 12 volt auxiliary battery to be recharged from the high voltage traction batteries. The electrical supply to the PEC is connected and isolated by power relays inside a contactor box, controlled by the ignition key and the electronic modules.

On-board microprocessors are linked by a multiplex database that allows synchronous, highspeed communication between all the vehicle’s systems. The vehicle system controller (VSC) acts as the user/vehicle interface and is operated by electrical signals from the accelerator pedal. This ‘drive-by-wire’ system has no mechanical connection to the speed controller. It is supplemented by a battery controller that monitors the sodium–sulphur operating temperature, the state of charge and recharging. The control system also incorporates a diagnostic data recorder which stores information from all the on-board electronic systems. This locates any operational malfunctions quickly and precisely.

A fault detection system (known as the power protection centre (PPC)), has also been built into the battery controller to monitor continuously the main electrical functions. Every 4 seconds it checks for internal and external leakage between the high-voltage system, the vehicle chassis and the battery case. Should a leak be detected in any wire, a warning light tells the driver that service action should be taken. The vehicle can then be driven safely for a short distance so that repairs can be made. If leakage is detected from both battery leads, the vehicle system cuts off the power to the motor and illuminates a red warning light. The auxiliary power supply is maintained to operate the battery cooling system. An inertia switch is also fitted, which is activated in the event of a vehicle collision and isolates power from the main battery pack. Auxiliary power to the battery coolant pump is also cut off to reduce the risk of hot fluids escaping. The vehicle incorporates a small amount of ‘creep’ whereby slight brake pressure is required to prevent it from moving forwards (or backwards when in reverse gear). This results in easier manoeuvring and smoother transmission of power. Auxiliary vehicle systems are powered by a standard automotive 12 volt lead–acid battery, the exception being the electrically driven cabin air conditioning system, which is powered directly from the main sodium–sulphur traction batteries, via a special AC inverter in the PEC module.

The climate control unit handles both the air conditioning and a highly efficient 4.5 kW ceramic element PTC heater. The heater elements are made from barium titanate with a multi-layer metallic coating on each side, impregnated with special chemical additives. The material has low resistance at low temperature for a very fast warm-up, while at higher temperatures the power supply is automatically regulated to save electrical energy. A strip of solar panels across the top of the windscreen supply power to a supplementary extractor fan that ventilates the cabin when the vehicle is parked in direct sunlight. This relieves the load on the air conditioning system when the journey is resumed. Some lightweight materials have been used in the Ecostar to offset the 350 kg weight of the battery pack.

Elimination of the clutch, torque converter and additional gearing is supplemented by a magnesium transmission casing, aluminium alloy wheels, air conditioning compressor and power electronics housing. Plastic composite materials have been used for the rear suspension springs, load floor and rear bulkhead. Use of these materials has helped keep the Ecostar’s kerb weight to between 1338 and 1452 kg, which is 25% heavier than a standard diesel-powered van. The vehicle

also has a useful load carrying capacity of up to 463 kg and retains similar load space dimensions to the standard Escort van. The Ecostar has been developed for optimum performance in urban conditions, where it is expected to be driven most frequently. Its top speed is restricted to 70 mph, whilst 0 to 50 mph takes approximately 12 seconds. Because of the high torque at low speed, acceleration from standing to 30 mph is quicker than diesel and petrol driven vehicles of the same size. The average vehicle range between charges to date has been 94 miles, with a maximum recorded range of 155 miles.

Powertrain: 3 phase, AC induction motor Transmission: Single-speed integrated Front-wheel drive

Power: 56 kW

Maximum torque (Nm): 193 Maximum speed (rpm): 13 500 Battery type: Sodium–sulphur Energy rating at 80% DOD: 30 kWh Power ratings:

peak intermittent (kW/bhp): 50/70 max continuous (kW/bhp): 30/40 On-board charger (120/240 V) with 2 metre charging cord on reel.

Required 240 V at 30 amp AC single phase for maximum charging rate

Maximum vehicle weight (kg): 1851 Kerb weight (kg): 1406

Payload (kg): 400–463

Rated top speed (governed): 70 mph Rated 0–50 mph acceleration: 12 seconds Range (Federal Urban Driving Schedule) 100 miles

Lightweight 14 inch aluminium alloy wheels with specially developed P195/

70R14 low resistance tyres

Fig. 5.21 Ecostar package, motor and specification.

Climate control module

Axel/differential

Hydraulic drum brakes

Tubular steel frame construction

Battery boxes Solid state speed controller location

Hydraulic disc brakes

Automatic charger location

Fig. 5.22 Bradshaw Envirovan.