Start with a vehicle design similar to a battery electric
vehicle, then eliminate the on board battery pack.
Add in a high voltage power connection in the rear of
the vehicle, and a trailer hitch.
Put the main power supply (either a battery pack or a
genset) onto a trailer, and attach it
to the rear of the
vehicle. The vehicle still has a 12-volt battery for
accessories, but no on-board motive power.
The power supply trailer has, on it's front, an electrical
connection and a trailer hitch connection to go to the
vehicle, and on it's rear, a power connection and trailer
hitch similar to the one on the rear of the vehicle. This
allows the vehicle to use either a battery, or a genset,
or both, or more than one of either or both.
The mechanical connection has both a yaw sensor and a
tension/compression sensor. The trailer's wheels have
both electrical power steering, and traction motors and
brakes. The steering of the trailer is automatically
controlled to keep the yaw angle very close to zero,
and the traction motors and (when necessary) brakes
are used to keep the measured tension/compression
very close to zero. This allows the car to be driven
almost as if the trailer were a weightless, rigid
The suspension of the trailer can be stiff (and therefor
energy efficient), with just enough dampening to
protect the cargo from being damaged by bumps in the
road, while the main vehicle's suspension can be as soft
or as firm as the driver chooses.
When a battery carrying trailer reaches the end of it's
life, it's easy to replace it, just by unplugging it
electrically and disconnecting the tow hitch.
To make moving these power supplying trailers easier,
each trailer would have two fully retractable caster
wheels: one front and one rear. When a key is put into
an "ignition" switch on the trailer and turned, these
wheels extend, and the power steering straightens the
left and right wheels; a human-operated joystick then
controls the traction motors in a manner similar to a
skid-steer vehicle. Basically, the trailer transforms into
a miniature (non-roadworthy) vehicle.
To make charging the battery pack super simple, if the
vehicle has a battery trailer attached, and is turned off
near a charging station, the battery trailer extends it's
caster wheels, disconnects from the vehicle, and
robotically drives itself to the charger, and plugs in. It
would move back to the car in response to a timer, or a
when it's fully charged, or when the driver presses a
button inside of the vehicle to recall the battery pack.
The fuel tank, or tanks, of the genset trailer would be
designed so that the center of mass of the fuel always
remains over the center of the axle (both left/right and
front/rear), regardless of whether full of fuel, or nearly
empty. Obviously the other components (whether with
the genset, or the battery) can be statically arranged to
If the vehicle is being for relatively short distances, a
battery pack trailer would be used. If the vehicle is
being driven hundreds of miles, both a battery pack and
a genset trailer would be used, much like a hybrid car.
The genset alone might be used, if the battery pack
reaches the end of it's life, and one is waiting for a
replacement for it... this last mode would of course be
less fuel efficient.
The same vehicle would be used regardless of whether
the genset is gasoline or diesel, or whether the battery
pack chemistry is lead, nickle, lithium, vanadium, etc.
Both types of power supplying trailer can (and should)
be made aerodynamic; and even if they were air
catching cubes (which they shouldn't be), they get to
ride in the vehicle's slipstream.
Cabin heating: This needs to be done through electrical
resistance, or by using the air conditioner as a heat
pump. Either is less efficient than using waste heat
from an engine.
Heat management: If the genset's engine can't take
advantage of the high pressure air in front of the
vehicle, cooling is less effective. It would be possible
to put a radiator in the front vehicle, and connect and
disconnect plumbing for coolant between the vehicle
and trailer, but it might be impractical.
The battery pack trailer also needs cooling, though not
as much as the genset. It might be nice to share a
cooling system with the genset, but this might be
Collisions: Measures need to be taken to prevent the
trailer(s) from flying through the vehicle, if the vehicle
crashes headlong into something.