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How Does Regenerative Braking Work?Hybrids and all-electric vehicles create
their own power for battery recharging through a process known as regenerative
braking (regen mode). 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
mx-sensor.
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. Take a
minute to read How Motors and Generators Work and then come back for the
low-down on the regenerative braking process. 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 regen 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
Launch
X431 Diagun
. 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.
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