Page 167 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CH AP TER 6 .1 Battery/fuel-cell EV design packages

rechargeable lead–acid batteries for a total of 72 V. All engine compartment (b). The ‘cold combustion’ of the
accessories, such as internal lights, windscreen wipers, fuel-cell reaction, hydrogen combining with oxygen to

and gauges, run off the 72 V system through a DC/DC form water, takes place at 80–90 C and a single cell de-
converter, which steps the power down to 12 V, so that all velops 0.6–0.8 V. Sufficient cells are combined to power
batteries discharge equally. This distributes power re- a 50 kW asynchronous motor driving the front wheels
quirements evenly across all 12 batteries and prevents one through a fixed gear reduction. The cell comprises fuel
or two of the batteries from draining prematurely. anode, electrolyte and oxygen cathode. Protons migrate
A battery warning indicator shows the current percentage through the electrolyte towards the cathode, to form
of battery power available, with a visual warning when water, and in doing so produce electric current. Prospects
battery charge is below 20%. An on-board battery charger, for operating efficiencies above 60% are in view, pending
featured on the Envirovan, can be used to recharge successful waste heat utilization and optimization of gas
the battery packs simply by plugging it into any standard paths within the system. The reforming process involved
240 V AC power socket. The entire 72 V system requires in producing hydrogen from the fuel involves no special
approximately 9.5 hours to fully charge the batteries from safety measures for handling methanol and the long-term
an 80% state of discharge (20% remaining charge). The goal is to produce no more than 90 g/km of CO 2 . In the
battery pack provides approximately 1000 recharging final version it is hoped to miniaturize the reformer, which
cycles before replacement is required. Battery packs are now takes up most of the load space, (c), and part of the
available for less than £1000 which equates to less than 2p passenger area, so that it also fits within the former engine
per mile. Recharging costs add an additional 1 p per mile compartment. Rate of production of hydrogen in the re-
giving a total cost per mile of 3p. A 20 bhp General former, and rate of current production in the fuel cell,
Electric motor has been designed for the Envirovan. A both have to be accelerated to obtain acceptable throttle
range of 8 hours/150 miles is available for the vehicle response times–the flow diagram is seen at (d). The
which measures 4.21 metres long 1.65 wide. It can ac- 20 second start-up time also has to be reduced to 2 sec-

celerate to 25 mph in 6 seconds and its controller can onds, while tolerating outside temperatures of 30 C.
generate up to 28 bhp for quick response. GM Opel was reportedly working in the jointly op-
erated Global Alternative Propulsion Centre (GAPC) on
a version of its fuel-celled MPV which is now seen as
6.1.7 Fuel-cell powered vehicles close to a production design. A 55 kW (75 hp) 3 phase
synchronous traction motor drives the front wheels
6.1.7.1 General motors Zafira projects through fixed gearing, with the complete electrome-
chanical package weighing only 68 kg (150 lb). With
GM and its Opel subsidiary had aimed at a compact a maximum torque of 251 Nm (181 lb ft) at all times it
fuel-cell driven vehicle, Fig. 6.1-23. By 2010, up to 10% accelerates the Zafira to 100 km/h (62 mph) in 16 sec-
of total sales are expected to be taken by this category. onds, and gives a top speed of 140 km/h (85 mph). Range
The efficiency of cells tested by the company is over is about 400 km (240 miles).
60% and CO 2 emissions, produced during the refor- In contrast to the earlier vehicle fuelled by a chemical
mation of methanol to obtain hydrogen, are about half hydride system for on-board hydrogen storage, this car
that of an equivalent powered IC engine. Fuel cells have uses liquid hydrogen. Up to 75 litres (20 gallons) is

already been successfully exploited in power generation, stored at a temperature of 253 C, just short of abso-
at Westervoort in the Netherlands, and experimental lute zero, in a stainless steel cylinder 1 metre (39 in) long
versions have been shown to successfully power laptop and 400 mm (15.7 in) in diameter. This cryostat is lined
computers. According to GM, in principle four basic with special fibre glass matting said to provide insulating
fuels are suitable: sulphur-free modified gasoline, a syn- properties equal to several metres of polystyrene. It is
thetic fuel, methanol or pure hydrogen. Modified gaso- stowed under the elevated rear passenger seat, and has
line is preferred because of the existing distribution been shown to withstand an impact force of up to 30 g.
infrastructure but CO 2 emission in reforming is higher Crash behaviour in several computer simulations also
than with methanol. Synthetic fuel and methanol can be been tested.
obtained from some primary energy sources including Fuel cells as well as the drive motor are in the normal
natural gas. Transportation and storage of hydrogen is engine compartment. In the 6 months since mid-2000
still at the development stage for commercial viability, the ‘stack’ generating electricity by the reaction of
Liquefying by low temperature and/or pressure being hydrogen and oxygen now consists of a block of 195 single
seen as the only means of on-vehicle storage. fuel cells, a reduction to just half the bulk. Running at

GM engineers have been working on a fuel-cell drive a process temperature of about 80 C, it has a maximum
version of the Zafira van (a) in which electric motor, output of 80 kW. Cold-start tests at ambient tempera-

battery and controller are accommodated in the former tures down to 40 C have been successfully conducted.

168