Hello everyone, I am Professor John Kelly
and this is the WeberAuto YouTube channel. I am honored to be a speaker at your event this
year in 2020 and I've been asked to speak about the Chevrolet Bolt EV. So sitting right behind me
here is our 2017 Chevrolet Bolt EV that belongs to our automotive department and I've shot many
videos and spent many many hours disassembling this car and putting it back together I was so
impressed by this car that I bought one of my own and my wife drives it every day it's a 2019 as you
can see here in this photo the Bolt EV is a very impressive car and the price of these cars has
come way down they've had a few hiccups as far as a few little troubles here and there as any brand
new car design would but I'm here today to show you the basics of the Chevrolet Bolt EV as far
as the power train electrical cooling battery everything that makes this vehicle move down
the road and I think you'll be impressed also so let's start with what actually makes this
car move down the road and that is the drive unit assembly, it is not a transmission it is
a combination of an electric motor and a gear reduction unit that we will look at here next okay
when we get right down to the heart of what makes the bolt EV move down the road it's this electric
motor right here this is a permanent magnet synchronous AC motor and it has 150
kilowatts of power and 360 newton-meters of torque, it has a maximum rpm of 8810 rpm as you
drive down the road it is housed inside the drive unit underneath the vehicle and that drive
unit includes these pieces right here as far as rotating mechanical moving
parts inside the vehicle so we've got the motor. the rotor of the motor right here the
stator is in the housing of the drive unit but this motor turns a drive gear right here and this
drive gear has 35 teeth and that drive gear turns what general motors calls the main shaft and
it has 73 teeth right here and 21 teeth right here so this gives us a gear reduction of
a little over 2:1 and then this is the equivalent of the
final drive pinion gear on any rear axle where we drive 71 teeth of the
ring gear of a normally open uh differential of an open style differential so
we have three major pieces here the drive motor the main shaft and the differential case
with the ring gear on it and so if we turn the rotor 7.051 revolutions we will get
one revolution of the ring gear for the driving of the tires and wheel assemblies
because they are connected directly through the side gears so here's a
side gear output shaft and it has the cv shaft going to the driver's side
that splines into it just like that and then on the passenger side reaching all the
way through the center of the electric motor to the other side gear in the open differential we have the left-hand output shaft
and the passenger side cv shaft to drive the right front tire
and the left front tire so left front right front as we rotate this one
single electric motor rotor we turn the main shaft it turns the differential case and through
the side gears we drive the left and right front tires now that that is simplicity that
is amazing this electric motor takes place of a typical internal combustion engine so we have
one moving part right there and then these this gear reduction unit right here that is also
inside the same housing underneath the the vehicle in the front there just has
this gear reduction unit to give us a 7.0518 to one gear reduction so no automatic transmission
clutch packs no shifting it's just a direct drive gear reduction unit and most electric
vehicles have something similar to this some of them use a planetary gear set for gear
reduction but the majority of the ones I have seen use this style of gear reduction, not all of
them have the shaft going right down through the middle of the rotor some of them they're offset
like on the teslas but we're here to talk about the Bolt EV and so this is what moves you down
the road everything else underneath the hood and the battery underneath the car
all those parts are there to make sure that we have power routed to the motor to give us
the proper rpm and the proper torque acceleration deceleration regenerative braking and so on that
we need while driving down the road and then we also have the rest of the vehicle which runs on
12 volts so we still have to have a 12-volt system and there's a conversion from the high voltage 400
volt system down to the 12-volt system we call it but it's really somewhere around somewhere around
14 volts so let's take a look underneath the car at the housing that this goes in it's called the
drive unit it has the motor on one side the gear reduction on the other and then we'll start
looking at the controls for making this motor move forward or backward if we want
to back up so let's go do that next okay we are over underneath the 2017
Chevrolet Bolt EV that our shop owns and I want to show you the drive unit and a few
other things that are here under the car while we've got it lifted on the hoist so the first
thing let's take a look at the drive unit itself okay from right here we have a left motor mount
and right over here we have the right motor mount this section right here these two coolant hoses uh
to the back right here this is the drive unit this side of the drive unit right here contains that
electric motor this section right here contains the main shaft and the final drive unit and our
axle shafts cv shafts going out uh the side um these two hoses right here are coolant hoses we
have an inlet on the left outlet on the right the coolant comes in goes through some channels and
there is transmission fluid the general motors Dexron hp fluid right above that transfers
the heat into the coolant and then it moves out I have one of these drive units on a
stand here let's take a look at it oh before we do take a look at it there are two
drain plugs one right there one right here this drain plug drains the fluid over here on
the gear side this drain plug drains the transmission fluid on the electric motor side they
are there are passages and openings that connect the two together but if you want to fully drain
it, you have to remove those two plugs and then there's another plug right up here that is used
for uh fluid level checking so you add fluid add another plug up higher there until fluid
comes out of the hole over there there's a special procedure to check the fluid properly there's an
electric uh pump that needs to be turned on with the scan tool and a few other things to make
sure that the fluid level is set correctly all right so let's take a look at the drive
unit on the engine stand that I have here okay this is a drive unit just like the
one that we have in the vehicle here I want you to see that it's tipped up 90 degrees
this is the bottom of the drive unit in the vehicle but the way the holding fixture holds it
it tips it sideways for service work so here's our coolant inlet and coolant outlet hoses remember
we just looked at those underneath the car right here on the front of the drive unit is the
electric air conditioning system compressor and it's high voltage cable here okay right here on
the passenger side of the drive unit we've got the fill plug and this is kind of hard to reach
from underneath the vehicle but that's where you're supposed to put the fluid in I suppose you
could put it in on the fluid level check plug area but this is the official field plug we have
an internal mode switch electrical connector here on this side also okay here on the driver's
side of the drive unit we have the electric oil pump this is a 12-volt oil pump and
then if we look at the top of the drive unit we have the transmission range selector actuator
so there's actually this gigantic electric motor assembly with gear reduction that moves a piece
of shift linkage to move a shift selector inside the transmission for when you change your
your gear shifter from parked reverse neutral drive and low now as we saw on the bench
over there the transmission does not shift now as we saw on the bench over there this
drive unit does not shift this is you could consider this a one-speed transmission but it has
an internal mode switch which is a feedback to the computer that controls the electric motor telling
it whether or not you've selected reverse now that seems like kind of a silly way to do things
because you would think they'd just read it off the shifter but it's read off of the internal mode
switch and the actuator here, it has no mechanical connection to the shifter in the vehicle so
it's kind of a strange setup it is possible to get locked into park if there's
a malfunction so as this shift actuator moves this linkage back and forth it actually can engage
the parking pawl or disengage the parking pawl besides rotating an internal sensor to determine
whether or not you've selected reverse or drive or low also on the top of the case here we have
a transmission oil sump cover where this 12-volt pump off to the side pumps fluid up into the top
there and then it drains down and cools the stator windings inside of this unit for the electric
motor and then there's one more electrical connector over here and that's for the resolver
which measures the speed direction and position of the electric motor rotor and there's
also a temperature sensor inside of here and then one last thing that you can't see is there's
actually a fluid filter in here that is not serviceable there's no recommended service date or
interval on that but the service manual does say if you ever take this apart you should change
the filter when you put it back together so this is the drive unit this is the equivalent
of the engine and the transmission of an internal combustion engine-powered vehicle all
in one now as you can see right here we have three orange cables coming off of the
electric motor and that these three go to the inverter assembly which is up underneath the
hood that we'll take a look at here in a moment that takes power from our DC battery underneath
the vehicle and converts it to AC to drive this electric motor so moving from the drive
unit now to the electronics that help control the motor that do control the motor these three
wires right here are how the power is transferred when you accelerate and when you decelerate for
regenerative braking and then we have sensors around on this drive unit to give feedback to
the computer that controls the transmission and I keep calling it a transmission but
it's a drive unit it's not a transmission okay well let's take a look at where these three
wires connect next okay I told you that the three orange wires coming from the drive unit assembly
that we just looked at went up underneath the hood to a part called the inverter general motors
calls it the single power inverter module the spin and I want to show you that but there are four big
boxes underneath the hood that we need to look at plus one more off to the side here that heats
the coolant going into the heater core to warm the passenger compartment so in all there
are five big boxes here underneath the hood and we can see the top of a power distribution
module underneath that is the inverter assembly that we just talked about off to the right
here is the dc to dc converter that takes our 400 volts and steps it down to around 14
volts to charge our 12-volt battery over here and to supply power for the rest of the vehicle
to run on because the rest of the vehicle other than the powertrain that we've looked at here
the drive unit and air conditioning compressor and some of the heaters are all 12 volt and
then underneath that dc to dc converter is the on-board charger module so that when you
plug in your charge cord to the side of the car it has to convert the ac power from the wall into
dc in order to charge the battery underneath the vehicle well I have all five of these pieces over
here on the workbench so let's go take a look at those now okay as we just saw under the hood
over there we have four big boxes and one other box off to the side that we need to discuss
we're wanting to see how does the power get to the drive unit so the way the power gets to the
drive unit is we start at the high voltage battery underneath the vehicle and that battery has a
connection to this high power distribution module on the back right here and then it splits up and
supplies power to the rest of these boxes and also a connection to the dc fast charge connector on
the side of the vehicle if you have dc fast charge but underneath that and fed power from this is the
single power inverter module or just the inverter this inverter receives power right
here on this electrical connector from the distribution box up here dc and
then on the back here we take off the plug there are our three-phase cable connections so
those three wires on that drive unit connect right here so we have DC power coming in from the
battery the inverter changes it to an ac signal to drive the motor while we're accelerating then
when we decelerate the motor becomes the generator feeds three-phase power back into the inverter
assembly where it runs it through a rectification process and feeds dc power back to the rest of the
system and to charge the battery for regenerative braking anytime you slow down and provided
there's enough room in the battery to accept it but it could also be used by other parts on the
vehicle other high voltage parts that need power all right this inverter assembly has two coolant
hose connections right here on the front and is liquid-cooled it has uh it's part of the
power electronics coolant loop underneath the hood and there are three different
reservoirs for coolant under the hood this is one of them or this is part of one of
them all right so this is the inverter assembly it has a low voltage connection
right here for communication with external computers but this is what drives the
electric motor inside of that drive unit okay this power distribution module also feeds power to
the dc to dc converter right here general motors calls it the accessory power module and I want you
to notice right here I bought this one off of a wrecked vehicle in a salvage yard it has the
battery positive terminal right there so we have battery positive output our charging system
output this would be the same as an alternator's B terminal the feeding the battery this is our
ground right here which the entire housing is it's case grounded but that is your ground cable that
goes over to the battery this is your positive cable that goes to the battery this is the dc
to dc converter it takes in 400-volt power from the battery steps it down to 14 volts right here
notice it is also liquid-cooled and has a black low voltage connection there for communication
and control with other modules on the vehicle so if you look directly under the hood
on the right-hand side you will see this accessory power module as general motors calls
it or dc to dc converter which is what it does right there under the hood now underneath this
is this next box that we need to talk about this box is the onboard charger module assembly
the OBCM and the onboard charger module is used when you plug in your j1772 charge connector
or whatever charge connector you have based on what country you're you're living in but
we have high voltage ac come in right here on this connector this is a, we've got
a four-pin connector in there so one here in the United States that's
between 110 and 240 volts and then we have an output from the onboard charger module
of 350 to 400 volts to charge the high voltage battery under the car while you've got that
charge connector plugged in so so high voltage AC in and high voltage DC out here's our black
electrical connector for communication with other on-board devices, this also gets
hot and needs to be cooled while charging this is only used when charging with an external
charge cord using ac voltage if we're using a dc fast charge this module is totally bypassed and we
go directly through the power distribution module we have power come in right here go
right back out and down to the battery to charge it more quickly not
used at all for dc fast charge okay so those are the four boxes that you
see under the hood and these four boxes sit on a bracket right on top of that drive
unit assembly that we just looked at so when you open the hood on the Chevrolet
Bolt EV and you see these four pieces you know just underneath it is the drive unit with
the electric motor and the gear reduction unit all right now off to the left under the
hood we have the cabin heater control module or coolant heater for the uh heater core
so we have an uh an inlet and an outlet I thought I had those marked but oh here they
are in on this side out on this side we have high voltage DC power from the distribution block right
here and then can communication line right there and this is a 7500 watt or 7.5-kilowatt heater
and this is a ceramic style heater ceramic element heater so this is another box under your hood
it's over there on the passenger side right tucked up against the hood hinge
so this gets hot to the touch that's normal the coolant reaches around 70 to 74
degrees celsius when it's on maximum all right I want to spend just a
little bit more time on this just distribution box so let me slide these other
pieces out of the way just for the moment on this distribution module
I've taken it apart and removed the internal pieces and then
I put them all back together in this housing right here so what i wanted
you to see is that we have a two wire electrical or two-terminal electrical connection
here that's the connection to the battery or from the battery and then these two
terminals have a direct connection over here to the output that goes down to the inverter
module then we have, notice three fuses right there, so these three fuses feed power to
the heater assembly that we just looked at the coolant heater that's his top fuse this middle
one right here comes out of this end connection here and that fuses the accessory power module
right there and then this bottom one the blue blue colored one feeds the
very end one right here which is the heater for the battery coolant
so we actually have two electric heaters on this vehicle one for the passenger compartment heat and
one for battery heat and when we put the vehicle back up in the air and look at the battery I'll
show you that so we have three fuses in this distribution block, I imagine
you can purchase those and replace them but you're not going to just easily
do that because this cover right here although it has a bunch of bolts going in from
the top there's two that come in from the bottom so you'd have to physically unbolt this
undo all the electrical connectors unbolt it and take the cover off to change those and
you should never undo any of these electrical connectors without going through the proper safety
training and following the correct depowering procedure to prevent yourself from getting
injured with potential high voltage situation now also on this distribution block, we have
an input from the DC fast charge so right here I have the charge receptacle used here
in the united states where we have the j1772 round connector five-pin connector there
and then two more pins right there at the bottom these two pins right there connect to these
two wires that plug into the front of this power distribution block so if you have a
bolt ev with dc fast charge it will have a cable plugged into the front of this you'll
notice you may have noticed the one under the hood of the car that we have does not have that i
didn't think we needed it for a training vehicle but that was a mistake for me because I actually
um discovered later that I wished I had it because I need to train other people on how the
the high current DC fast charge system works so it has a lot of additional
components it's not just this cable that are different even the internal pieces
in that distribution module are different there's an additional computer under the
driver's seat for power line communication with the external charger, there's additional
wire harnesses there's different programming for computers it's different yeah well
I already said different harnesses but inside of here, there are two additional
contactors that connect these two terminals from the DC fast charge to these two terminals
on the back to feed the battery to charge it so we won't spend any more time we could spend
hours and hours and hours on the electrical system here but this is just kind of an introductory portion or but this is just kind of
an introductory video to the Bolt EV but i wanted to show you what the major parts were
under the hood so so you'll know what those are nothing mysterious and then the
drive unit underneath and then the only thing left that we need to look
at as far as uh major components are is under the vehicle, we have our high voltage
battery and our battery heater and then we've got the cooling systems the three cooling
systems to look at so let's put the vehicle up in the air and take a look at the high voltage
battery and the high voltage battery heater okay here we are under the vehicle
the battery the high voltage battery is this entire bottom of the vehicle this
black metal section, it goes all the way back to the rear suspension so it starts right
here it's the width of the underbody and it moves all or it goes all the way up to right
here so it is a very large physical battery and it has 96 cell groups at 3.7 volts each for
358 volts nominal and 384 volts approximately when fully charged this is a liquid cooled
battery and so if we look right here we have inlet to the battery and an outlet these two
hoses right here and the inlet comes over and runs through this battery coolant heater so if we
want to heat the coolant going into the battery then we turn that heater on if we want to
cool the coolant going into the battery there's a chiller that's part of the air conditioning system
it's like a little mini evaporator that's up under the hood it's kind of buried you can't see it
very well but that same coolant runs through that as it does the heater but we don't
have those on at the same time so we have a battery heater it's a high voltage heater
we have an orange cable connected to that inlet and outlet there's a special
coolant flushing or bleeding procedure there is a five year 150 000 mile
scheduled maintenance and there's a lot of maintenance on this vehicle a lot of
people think it's just tires and wiper blades no, you read your owner's manual there's a lot of
stuff including a monthly underbody car wash if possible to help keep everything clean underneath
the vehicle so what else do we have here connected to the battery, we have these two big orange heavy
cables right here those are the two heavy cables that go up to the back of that inverter that then
creates the AC voltage three-phase AC voltage to drive the electric motor in the drive unit
we have a high voltage orange connection here a smaller connector and that is the connector
that's used when you plug in your charger charge cable or charge cord to the side of
the vehicle um that is a low amperage charge and the dc fast charge bypasses that little
tiny connector and comes right in on the large connector right there are two ground bonding
wires over here to establish a common ground and then there are two black electrical connections
over here for data communication and uh monitoring of circuits and and
feedback and so on in the battery some of you may have heard that just recently
there was a recall for some Chevrolet Bolt EV batteries catching on fire and the recall was
telling the customer to not charge the battery to 100 percent to charge it
to a lower amount, there's a video from Chevrolet that explains how to do that
using these software selections in the vehicle or if you take it to a dealer they will reprogram the
HPCM2, the computer that controls this to prevent a charge higher than 90 percent while they are
investigating the cause of the battery fires it's my understanding there have just been
a few battery fires five to seven I think out of close to seventy thousand vehicles sold but
it's that's enough to make me concerned because i told you I own a Bolt EV and my wife drives it. I
want to make sure that she is safe and so we have made the adjustments to only charge to 90 percent
maximum but we were all only charging to 80 anyway so I guess we'll see what happens with the
the Bolt EV battery recall whether they change the batteries or if it's a software fix or whatever
they're going to do if you are interested in what's inside the battery I have a whole bunch of
videos on disassembling the battery and showing you what's inside one word of caution there is a
center of gravity point right here it's labeled CG it's there to center your lifting table so
that it stays balanced when you lower it okay all right as we finish up this introduction
to the Chevrolet Bolt EV, I just want to talk briefly about the three different
coolant reservoirs that are under the hood so starting back here with the heater coolant
reservoir this reservoir has a pipe that goes straight down to a pump and then that pump
pumps coolant up into our heater assembly our ceramic heater then it goes over and into the
heater core under the instrument panel here to heat the coolant going into the heater core
for passenger compartment heat and then it returns back to the reservoir itself
so it just makes one big loop all right the next reservoir under the hood
right here on the passenger side is for the high voltage battery the coolant loop associated
with the high voltage battery so just like the the other reservoir there this reservoir
has a hose that goes straight down to a pump where it pumps it to that heater that we looked
at underneath the car then it goes into the battery comes back out of the battery goes to a
chiller assembly that's here underneath the hood that removes heat from the coolant if it's
too hot and then back to the reservoir itself so that is a second coolant loop on this vehicle
okay our third coolant reservoir on the driver's side under the hood here is for what I call the
power electronics coolant loop so just like these other reservoirs there's a hose that goes straight
down to a pump that pump then sends coolant to the inverter assembly under this distribution block
then it comes over to the accessory power module or the dc to dc converter then it goes down
to that box underneath that to the onboard charger module then it goes down to the drive
unit assembly and then back to the reservoir itself this vehicle does not have a radiator
in the traditional sense, it only has an air conditioning condenser system so since the air
conditioning system cools the battery coolant that heat is dissipated through the regular
air conditioning condenser assembly up front so there is no radiator it looks
like a radiator but it's just the condenser for the air conditioning system okay
well this has been a brief introduction to the 2017 through 20 Chevrolet Bolt EV there have
been some changes improvements from 2017 up through 2020 but overall the system functions
the way the same way that we've described here there are new there's a new Chevrolet
Bolt design supposed to be coming out in a little bit larger of a vehicle uh 2022
or so I'm excited to see what that brings with it and what other improvements there
will be there's always an improvement with the next model year some change
that's taken place but with what I've shown you here under the hood of this Chevrolet Bolt EV all
these individual components you could now go to any electric vehicle and find pretty much the
same components they may not be all individual pieces they might be combined into one piece
or two or three pieces instead of four or five they might have hard busbar connections instead of
loose wire connections but every electric vehicle I've ever seen has these same components just
different sizes different locations and so on so if you can understand the basic operation
of the Chevrolet Bolt EV that really will help you into in understanding any electric vehicle
that's out there right now and it'll help you tremendously towards understanding hybrid vehicles
as well well I hope this has been beneficial to you once again it's an honor to be a speaker for
your event and I appreciate that have a good day
Prof. Kelly was one of the first videos on YT that made me understand Toyota's planetary gearset hybrid transaxle in detail. He also goes to disassemble other popular transaxle & transmissions like the ZF 8spd, ZF 9spd, Honda 5AT, Lexus 8AT etc.
His videos are LENGTHY, but if you have time to waste because of lockdown, it is very educational to a gearhead.
This professor and program are fantastic, Im so glad they take the time to upload to YouTube.
As a soon-to-be-graduating ME, this guy is amazing. I wish I'd discovered him sooner. He's able to break complex things down so well.
Who's gonna have to be the first mechanic to tell someone the oil pump went bad on their EV. "OH SURE PAL"
@11:30
This guy is amazing. Thanks for posting this!
I love this channel.
Particularly I like how straightforward he is. No clickbait or sensationalism. Just proper education.
Every video this guy makes is pure gold. Watching him tear down the bolts transmission/motor assembly and reveal that it has only four or five moving parts.... Beautiful.
Can he explain Tesla