The Power Behind Hybrid and Electric Vehicles
With an increase in today’s hybrid sales, consumers are curious about the workings
behind this technology. The following blog will cover detailed info on the hybrid
process to help you better understand it.
Hybrids and all-electric vehicles create their own power for battery recharging
through a process known as regenerative braking. We've explained what regenerative
braking is and how the process works in general terms, but many folks are interested
in the deeper nuts and bolts of electricity generation. They understand that in
a hybrid or all-electric vehicle the word "regenerative," in terms of regenerative
braking, means capturing the vehicle's momentum (kinetic energy) and turning it into electricity that recharges
(regenerates) the onboard battery as the vehicle is slowing down and/or stopping.
It is this charged battery that in turn powers the vehicle's electric traction motor.
In an all-electric vehicle, this motor is the sole source of locomotion. In a hybrid,
the motor works in partnership with an internal combustion engine. But that motor
is not just a source of propulsion, it's also a generator.
Any permanent magnet motor can operate as either a motor or generator. In all-electrics
and hybrids, they are more precisely called a motor/generator (M/G). But the technologically
curious want to know more, and they'll often ask "How, and by what mechanism or
process, is the electricity created?" It's a good question, so before we get started
explaining how M/Gs and regenerative braking work in hybrids and electric vehicles,
it is important to have basic knowledge about how electricity is generated and how
a motor/generator functions.
So How Does a Motor/Generator Work in an Electric or Hybrid Vehicle?
No matter the vehicle design, there must be a mechanical connection between the
M/G and the drivetrain. In an all-electric vehicle there could be an individual
M/G at each wheel or a central M/G connected to the drivetrain through a gearbox.
In a hybrid, the motor/generator could be an individual component that is driven
by an accessory belt from the engine (much like an alternator on a conventional
vehicle--this is how the GM BAS system works), it could be a pancake M/G that is bolted
between the engine and transmission (this is the most common setup--the Prius, for example), or it could be multiple
M/Gs mounted inside the transmission (this is how the
two-modes work). In any case, the M/G has to be able to
propel the vehicle as well as be driven by the vehicle in regen mode.
Propelling the Vehicle with the M/G Most, if not all, hybrids and
electrics use an electronic throttle control system. When the throttle pedal
is pushed, a signal is sent to the onboard computer, which further activates a relay
in the controller that will send battery current through an inverter/converter to
the M/G causing the vehicle to move. The harder the pedal is pushed, the more current
flows under direction of a variable resistance controller and the faster the vehicle
goes. In a hybrid, depending upon load, battery state-of-charge and the design of
the hybrid drivetrain, a heavy throttle will also activate the internal combustion
engine (ICE) for more power. Conversely, lifting slightly on the throttle will decrease
current flow to the motor and the vehicle will slow down. Lifting further or completely
off the throttle will cause the current to switch direction--moving the M/G from
motor mode to generator mode--and begin the regenerative braking process.
Regenerative Braking: Slowing the Vehicle and Generating Electricity
This is really what the regenerative mode is all about. With the electronic throttle
closed and the vehicle still moving, all of its kinetic energy can be captured to
both slow the vehicle and recharge its battery. As the onboard computer signals
the battery to stop sending electricity (via the controller relay) and start receiving
it (through a charge controller), the M/G simultaneously stops receiving electricity
for powering the vehicle and starts sending current back to the battery for charging.
Remember from our discussion on electromagnetism and motor/generator action: when
an M/G is supplied with electricity it makes mechanical power, when it's supplied
with mechanical power, it makes electricity. But how does generating electricity
slow the vehicle? Friction. It's the enemy of motion. The armature of the M/G is
slowed by the force of inducing current in the windings as it passes over the opposing
poles in the magnets in the stator (it's constantly battling the push/pull of the
opposing polarities). It is this magnetic friction that slowly saps the vehicle's
kinetic energy and helps scrub off speed.