Lightweight Electric/Hybrid Vehicle Design

Current EV design approaches 9
with 110/0/110) the potential of the vehicle electrics is balanced to earth. When one end is
earth (typical European situation) the potential of the vehicle electrics will move up and
down at the supply frequency with respect to ground and there is the prospect of earth leakage
current through any capacitance to earth of the vehicle electrical system. However, this is
very small, usually because the tyres isolate the vehicle. However, when charging it would be
desirable to ground the vehicle body to prevent any shocks from people touching the vehicle
and standing on a grounded surface.
1.2.7 ELECTRIC VEHICLE SPECIFICATIONS
From the previous considerations one can now start the task of specifying EV capability/
performance trade-offs. Polaron believe EVs will be partitioned as shown in Fig. 1.6. This does
not pretend to be an exhaustive list but to show the range and scale of requirements to be provided
for. The most interesting observation is that in the mass market, 30–150 kW, a solution is possible
using just two sizes of drive, 45 and 75 kW. To complement the drives, motors are required of two
speed ratings for each size, say 5000 rpm where compatibility with a prime mover is required, and
12 000 rpm for the direct drive series hybrid/pure electric case.
1.2.8 HYBRID VEHICLE EXAMPLES
It is now proposed to have a look at two cases (a) 45 kW parallel hybrid vehicle; (b) 90 kW
series hybrid vehicle, as in (Fig. 1.7). The 45 kW parallel hybrid vehicle consists of, typically,
a small engine driving through a motor directly into the differential gear and hence to the road
wheels. Minimization of weight is the key issue on such a design along with low rolling resistance
and low drag. At 60 mph a good design can expect to draw 8 kW to keep going on a flat level
road. The vehicle would be fitted with an engine rated to supply about one-third of the peak
requirement, that is 15 kW plus an allowance for air conditioning if relevant. The motor has to
deliver up to 45 kW using energy stored in batteries. This can be done either by a constant
torque motor operating via a gearbox or a constant power motor operating with only two gears
Power GVW Engine Motor Motor Turbo Application
Rating type rating alternator
Below Less than None Brush DC Up to None Straight battery
40 kW 2 tons 40 KW electric van or car
40 kW 2 ton IC Brushless DC 1 x 45 kW None Parallel hybrid
−150 kW 5000 rpm family car
2 ton GT Brushless DC 1 x 75 kW 1 x 100 kW Parallel hybrid
12 000 rpm 60 000 rpm performance saloon
3 ton IC Brushless DC 1 x 75 kW None Parallel hybrid
5000 rpm 1 ton truck
5 ton GT Brushless DC 2 x 45 kW 1 x 100 kW Series hybrid
12 000 rpm 60 000 rpm 2 ton truck
7 ton GT Brushless DC 2 x 75 kW 1 x 150 KW Series hybrid
12 000 rpm 50 000 rpm single deck bus
150 kW 10 ton GT Switched 1 x rating 1 x rating Heavy traction
to reluctance 5000 rpm 50 000 rpm and road haulage
motor at 150 kW
1 MW 25 000 rpm Series hybrid
40 tons at 1 MW configuration
Fig. 1.6 Short-term battery electric and hybrid vehicles.