Page 158 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Battery/fuel-cell EV design packages CHAPTER 6.1

speed dual reduction planetary gear set with a ratio of corrosion resistant and are made from SMC and RIM
10.946:1. The second generation propulsion system has polymers. The EV1 is claimed to be the most aero-
an improved drive unit, battery pack, power electronics, dynamic production vehicle on the road today, with
6.6 kW charger, and heating and thermal control module. a 0.19 drag coefficient and ‘tear drop’ shape in plan view,
Now, 26 valve-regulated, high capacity, lead–acid (PbA) the rear wheels being 9 inches closer together than the
batteries, 12 Veach, are the standard for the EV1 battery front wheels. The EV 1 has an electronically regulated
pack and offer greater range and longer life. An optional top speed of 80 mph. It comes with traction control,
nickel–metal hydride battery pack is also available for the cruise control, anti-lock brakes, airbags, power windows,
Gen II model. This technology nearly doubles the range power door locks and power outside mirrors, AM/FM
over the first generation battery and offers improved CD/cassette and also a tyre inflation monitor system.
battery life as well. The EV1 with the high capacity lead-
acid pack has an estimated real world driving range of 6.1.5.3 AC drives
55 to 95 miles, depending on terrain, driving habits and
temperature; range with the nickel–metal hydride pack is An interesting variant on the AC-motored theme,
even greater. Again, depending on terrain, driving habits, Fig. 6.1-16, is the use of a two-speed transaxle gearbox
temperature and humidity, estimated real world driving which reduces the otherwise required weight of the high
range will vary from 75 to 130 miles, while only 10% of speed motor and its associated inverter. A system de-
power is needed to maintain 100 km/h cruising speed, veloped by Eaton Corporation is shown at (a) and has a
because of the low drag, now aided by Michelin 4 kW battery charger incorporated into the inverter. A
l75/65R14 Proxima tyres mounted on squeeze-cast alu- 3 phase induction motor operates at 12 500 rpm – the
minium alloy wheels. speed being unconstrained by slip-ring commutator
The 1990 Impact prototype from which the EV1 was systems. A block diagram of the arrangement is at (b) and
developed had one or two more exotic features which is based on an induction motor with 18.6 kW 1 hour
could not be carried through to the production derivative rating – and base speed of 5640 rpm on a 192 V battery
but claimed an urban range of 125 miles on lead–acid pack. The pulse width modulated inverter employs 100
batteries. In the Impact the 32 10 volt lead–acid batteries A transistors. The view at (c) shows the controller drive
weighed 395 kg, some 30% of the car’s kerb weight, system functions in association with the inverter. In an
housed into a central tunnel fared into the smooth AC induction motor, current is applied to the stator
underpanel and claimed to have a life of 18 500 miles. windings and then induced into the windings of the rotor.
The Impact weighed 1 tonne and accelerated from 0 to Motor torque is developed by the interaction of rotor
100 kph in 8 seconds, maximum power of the motor currents with the magnetic field in the air gap between
being 85 kW. The vehicle had 165/65R14 Goodyear low- rotor and stator. When the rotor is overdriven by coasting
drag tyres running at 4.5 bar. Two 3 phase induction of the vehicle, say, it acts as a generator. Three phase
motors were used, each of 42.5 kW at 6600 rpm; each winding of the stator armature suits motors of EV size;
can develop 64 Nm of constant torque from 0 to 6000 the rotor windings comprise conducting ‘bars’ short-
rpm, important in achieving 50–100 km/h acceleration in circuited at either end to form a ‘cage’. Rotation speed of
4.6 seconds. Maximum current supply to each motor was the magnetic field in the air gap is known as the syn-
159 A, maximum voltage 400 V and frequency range chronous speed which is a function of the supply-current
0–500 Hz. The battery charger was integrated into the frequency and the number of stator poles. The running
regulator and charging current is 50 A for the 42.5 Ah speed is related to synchronous speed by the ‘slip’.
lead–acid batteries, which could at 1990 prices be If two alternators were connected in parallel, and one
replaced for about £1000. was driven externally, the second would take current from
The EV1 can be charged safely in all weather the first and run as a ‘synchronous motor’ at a speed
conditions with inductive charging. Using a 220 volt depending on the ratio of each machine’s number of poles.
charger, charging from 0% to 100% for the new lead–acid While it is a high efficiency machine which runs at con-
pack takes up to 5.5–6 hours. Charging for the nickel– stant speed for all normal loads, it requires constant cur-
metal hydride pack, which stores more energy, is 6–8 rent for the rotor poles; it is not self-starting and will stop
hours. Braking is accomplished by using a blended com- if overloaded enough for the rotor to slip too far behind
bination of front hydraulic disk, and rear electrically the rotating stator-field. Normally, the synchronous
applied drum brakes and the electric propulsion motor. motor is similar in construction to an induction motor but
During braking, the electric motor generates electricity has no short-circuited rotor – which may be of the DC-
(regenerative) which is then used to partially recharge excited, permanent-magnet or reluctance type.
the battery pack. The aluminium alloy structure weighs The view at (d) shows a stator winding for a 2 pole
290 pounds and is less than 10% of the total vehicle 3 phase induction motor in diagrammatic form. If supply
weight. The exterior composite body panels are dent and current frequency is f s , then stator field speed is f s /p for

159