Page 166 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Battery/fuel-cell EV design packages CHAPTER 6.1

information from all the on-board electronic systems. A strip of solar panels across the top of the windscreen
This locates any operational malfunctions quickly and supply power to a supplementary extractor fan that
precisely. ventilates the cabin when the vehicle is parked in direct
A fault detection system (known as the power pro- sunlight. This relieves the load on the air conditioning
tection centre (PPC)), has also been built into the battery system when the journey is resumed. Some lightweight
controller to monitor continuously the main electrical materials have been used in the Ecostar to offset the
functions. Every 4 seconds it checks for internal and 350 kg weight of the battery pack.
external leakage between the high-voltage system, the Elimination of the clutch, torque converter and ad-
vehicle chassis and the battery case. Should a leak be ditional gearing is supplemented by a magnesium
detected in any wire, a warning light tells the driver that transmission casing, aluminium alloy wheels, air condi-
service action should be taken. The vehicle can then be tioning compressor and power electronics housing.
driven safely for a short distance so that repairs can be Plastic composite materials have been used for the rear
made. If leakage is detected from both battery leads, the suspension springs, load floor and rear bulkhead. Use of
vehicle system cuts off the power to the motor and il- these materials has helped keep the Ecostar’s kerb
luminates a red warning light. The auxiliary power supply weight to between 1338 and 1452 kg, which is 25%
is maintained to operate the battery cooling system. An heavier than a standard diesel-powered van. The vehicle
inertia switch is also fitted, which is activated in the also has a useful load carrying capacity of up to 463 kg
event of a vehicle collision and isolates power from the and retains similar load space dimensions to the stan-
main battery pack. Auxiliary power to the battery coolant dard Escort van. The Ecostar has been developed for
pump is also cut off to reduce the risk of hot fluids es- optimum performance in urban conditions, where it is
caping. The vehicle incorporates a small amount of expected to be driven most frequently. Its top speed is
‘creep’ whereby slight brake pressure is required to restricted to 70 mph, whilst 0–50 mph takes approxi-
prevent it from moving forwards (or backwards when in mately 12 seconds. Because of the high torque at low
reverse gear). This results in easier manoeuvring and speed, acceleration from standing to 30 mph is quicker
smoother transmission of power. Auxiliary vehicle sys- than diesel and petrol driven vehicles of the same
tems are powered by a standard automotive 12 volt lead– size. The average vehicle range between charges to date
acid battery, the exception being the electrically driven has been 94 miles, with a maximum recorded range of
cabin air conditioning system, which is powered directly 155 miles.
from the main sodium–sulphur traction batteries, via
a special AC inverter in the PEC module.
The climate control unit handles both the air condi- 6.1.6.6 Bradshaw envirovan
tioning and a highly efficient 4.5 kW ceramic element
PTC heater. The heater elements are made from barium DC drive is used on the higher payload capacity purpose-
titanate with a multi-layer metallic coating on each side, built Bradshaw Envirovan. Fig. 6.1-22 shows the Envirovan
impregnated with special chemical additives. The ma- built in conjunction with US collaborator Taylor-Dunn.
terial has low resistance at low temperature for a very fast This can carry 1500 lb on a 3.55 square metre platform at
warm-up, while at higher temperatures the power supply speeds up to 32.5 mph and is aimed specifically at city
is automatically regulated to save electrical energy. deliveries. The vehicle relies on 12.6 volt deep-cycle,

Fig. 6.1-22 Bradshaw Envirovan.

167