Throughout my career as a mechanic, I’ve worked on trucks, trailers, vans, cars, buses, cranes, and even airport ground gear.
HGVs are what I trained on as an apprentice many years ago but over the last 5 or 6 years I’ve found myself working solely on cars. Trucks are much more fun to work on and with everything being so big you always remain childlike while around them. I loved my days as a young apprentice and it's probably due to the entire HGV industry having such an adolescent sense of humour woven into it. I mean what 16-year-old wouldn't find it funny when asked to go service a truck's "grease nipples"? Truth be told I still snigger at the terminology now, and I'm 42-years old! And then there are male and female parts to fit, "male" being anything that goes into something and "female" being a part that gets entered by its male counterpart. In fact, the whole industry is just one big innuendo and HGV mechanics revel in it. It's honestly the perfect career for a man-child like myself.
Domestic vehicles, on the other hand, are built with the consumer in mind and are therefore a royal pain in the backside to work on, french cars being especially so. Take Renault for example. Here is a manufacturer that decided it would be a good idea to place the access panel for the pollen filter right next to the clutch pedal, meaning that this serviceable item requires the removal of the entire clutch pedal mechanism before it can be replaced. Madness. Knowing this helps you to understand why car mechanics are generally grumpy gits. I have no love for cars and IMO they do nothing for me other than getting me from A to B. Conversations involving BHP, mapping, or twin turbos will put me to sleep faster than a right hook from Mike Tyson. For me, cars are like porn stars. They may look good on the outside and they may even give you the ride of your life, but if you have to look after one you’ll soon learn that what you actually have is an over-complicated, swiftly depreciating, mega-bitch who's ready to empty your wallet at a moments notice.
So why the heck have I chosen to work on them, you might ask? Well, the simple answer is, I just love taking things to pieces, finding out what's wrong, fixing it, and then building it all back together again. And even though cars may not possess any wow factor for me, they still have an engine, and just the thought of how an engine works with all those moving parts coming together in near-perfect harmony and absolute synchronicity will always be something that fascinates me. Suck, squeeze, bang, blow! A 4-stroke symphony and a miracle of engineering, whether it be performed on a 6-cylinder 8.3lt Cummins engine or a 2-cylinder twin air 875cc Fiat 500. Combustion engines rock!
There's A New Kid On The Block
By now most of us are well accustomed to seeing, not hearing, electric cars driving on the roads. Tesla seems to be the poster boy of the industry and the reason I say that is because my 8-year old step-son literally freaks out every time he sees one, much like I used to when I was his age and I saw a Porsche. Tesla cars don’t do much for me, in fact, the whole EV(electric vehicle) styling department needs to have a word with itself. Maybe they’ve all seen too many sci-fi movies and can’t imagine anything other than blocky shapes and harsh angles. There are exceptions of course and one that springs to mind is the BMW i8.
Wowza! Now that is one sexy-looking EV. Well, in actual fact the BMW i8 isn’t an EV, it’s a PHEV (Plug-in Hybrid Electric Vehicle), which brings me nicely on to one of the interesting and lesser-understood elements within the world of electric vehicles...
So what type of EV would you like? Plug-in? Hybrid plug-in? Maybe you'd like an MHEV (Mild Hybrid Electric Vehicle)? And have you put any thought into the power source configuration? I mean we have Toyota's very own Hybrid System? Or you might prefer the Series Hybrid System?...Hmmm, I'm not so sure though, you look like someone who'd enjoy a Parallel Hybrid System...Am I right?
I bet you didn't realise there was so much choice in the EV market? But don't threat, it's not as confusing as it seems. Let me break it down for you.
As for the power source configuration, well, there isn't much for you to think about, as 75% of the entire EV fleet has the parallel hybrid system powering you down the road. "But what the heck is a Parallel Hybrid System?", I hear you ask...(Don't worry, this won't take long to explain)
Note: Before we go any further, one fundamental priciple of electric vehicles must be understood.
No matter what EV we speak about, be that EV, HEV, PHEV, or MHEV, the battery pack will always supply and store DC(Direct Current) voltage to the inverter. This is simply because DC can be stored in a battery whereas AC can not. DC voltage is then sent from the battery to an inverter which turns DC into AC. AC voltage is then sent to a Motor Generator that turns AC electrical energy into kinetic energy to enable the wheels of the vehicle to rotate. The Motor Generator is named as such because it has two functions; one is to act as a motor to power the vehicle and the other to act as a generator to generate electricity in order to recharge the battery (The process of recharging the battery is called Regenerative Energy Recovery, which we will come to later on).
Series Hybrid
As the picture illustrates, in a series hybrid configuration there is no direct drive between the combustion engine and the driven wheels. This means the car can not have mechanical and electrical energy driving the wheels at the same time. The on-board computer will choose, depending on the driving conditions, whether the inverter powers the AC generator using the engine or the battery. However, even when the vehicle is being powered by its combustion engine, the engine is in-fact powering an electric motor and not the wheels directly.
Parallel Hybrid System
As I mentioned before, this configuration is the most commonly used throughout the industry. As you can see, the main difference here is that there is a transmission box bolted between the engine and motor generator, creating a direct drive-line from engine to wheels. In a parallel hybrid system, both battery and engine can simultaneously supply power to the wheels. This utilises both power sources during their optimum output range.
Interesting fact time!
Combustion engine suck when it comes to instant power but perform excellently through mid-range revs, ie 3rd and 4th gear. Contrastingly, electric motors give great performance and extraordinary power at low revs, but then tend to tether off once they getting to mid-range. Together, electric motors and combustions engines compliment each other perfectly, filling in where the other lacks performance and therefore enabling maximum power throughout its range. Here is a simple graph to help explain this concept...
Toyota Hybrid System
Here’s where things get slightly more complicated with Toyota’s Hybrid System.
The Toyota Synergy Hybrid incorporates an ICE (internal combustion engine) and 2 motor generators, MG1 & MG2. The purpose of MG1 is to start up the combustion engine and to recharge the high voltage battery during regenerative energy recovery. While the purpose of MG2 is also to recharge the high voltage battery, it’s main function is to drive the wheels via a CVT (constant velocity transmission or constantly variable transmission). The power from the ICE and MG2 is managed by the PSD (Power Splitting Device). MG1, MG2, the PSD, and the CVT are all housed in what’s called a “Transaxle”.
Constantly Variable Transmission
Regular transmissions use a series of gears that are selected by either the driver moving the gear lever (manual transmission) or automatically by the transmission control module (automatic transmission). The different gear ratios allow for the vehicle to move smoothly through its speed range. However, this conventional type of transmission is limited to the ratios of the gears within the gearbox. For example, 1st gear is for speeds of 0 to 10mph and 2nd gear is for 10mph to 20mph, and so on until you reach top gear (5th or 6th). The CVT on the other hand has no such limitations as it can change seamlessly through a continuous range of gear ratios allowing the power source to operate at its optimal RPM throughout the speed range. CVTs are found in many EVs but the CVT itself is nothing new. Subaru where using this technology back in the 1980’s.
Fully electric vehicles, in most instances, have only one gear that will propel the vehicle through its complete speed range. It is only when there is an additional ICE that there becomes the need for a conventional automatic transmission unit or a CVT.
Power distribution
I mentioned earlier how hybrid vehicles utilise the high voltage battery and the internal combustion engine to allow maximum efficiency throughout the power range. Below are a series of images to help better understand at what points each power source is used to enable optimal efficiency.
Regenerative Energy Recovery
For me, this is the part where EVs get really interesting. Regenerative energy recovery is something all electric vehicles do and they do this while decelerating. Deceleration may occur through braking via the brake pedal or simply through what is commonly known as engine braking.
While driving there are often time when you take your foot off the accelerator and allow the vehicle to slow down without using the brakes, this is a form of engine braking. In this scenario the engine is no longer driving the wheels, momentum is now the driving force propelling the vehicle. The longer you coast in this state the slower your vehicle will go. This deceleration is caused by the frictional forces created by the gears inside the gearbox. This friction uses up the kinetic energy and unless you apply power to drive those gears your car will eventually come to a complete stop. In a conventional vehicle this kinetic energy is allowed to go to waste but it an EV this momentum is used to drive the motor generator, turning what used to be an electric motor into an electric generator. The electricity created by the wheels of the car driving the motor generator is then sent to the inverter where the AC voltage is converted to DC voltage which in turn is then sent to the high voltage battery.
Clever stuff! But wait, it’s gets better…
They’re brakes, Jim, but not as we know them.
So, you think that’s your brakes slowing you down…? Think again. In an EV your brake pedal is nothing more than a lever which, depending on how hard you press the pedal, sends an electrical signal to a computer which then interprets your action and decides how much “braking” has been requested by the driver. The fact that this is all done in a fraction of the time it takes to say “fuck, that’s fast” is amazing enough. But what’s even more amazing than that is how the computer makes you think your brakes are slowing you down, when in actual fact what is happening is the electro-magnets inside the motor generator are being powered up. This results in an increase in the magnetic force which in-turn increases the effort required for the rotor arm to turn past the electro-magnets. The rotor arm of the motor generator are what drive the wheels of the car, and if the rotor arm has to pass a very strong magnet in order to turn, then this means that magnet will slow you down. Here is a short video I’ve found on YouTube which helps illustrate this process.
(Video created by Alex Sibila)
Respect The High Voltage Battery, Because Your Life Depends On It.
Make a mistake while working on the high voltage system of an EV and it could quite possibly be the last mistake you ever make. This was something my tutor said over and over again during my recent EV training course. At the time of writing this post, I am a level-3 EV technician, which means I am less likely to be found melting underneath the bonnet of an EV.
One of the items of safety equipment you use when working on any EV is a long pole with a hooked end, amusingly named the “Bo-Peep hook”. During training we were shown this hook and asked what it would be used for. “It’s to pull the mechanic clear of the vehicle in the case of an electric shock”, I replied. The tutor responded with a comment that will stick with me until the day I retire. He said, “Well, you’re kind of right, but you’ll more likely be pulling pieces of a person away from the car rather than a full person. These batteries hold 201.6v and the AC motors create 500v. At these kinds of voltages you don’t get a second chance or a close call”. To make sure I got the point he went on to tell me how the power surge will “split you open like the skin of a sausage”…Gulp!
As a level-3 HV technician, I can now confidently check and isolate the high voltage battery, allowing me to work on the high voltage components. The high voltage components consist of; the battery, the inverter, the air conditioning pump, the high voltage cooling system, and the motor generators. My training allows me to remove all but one of these components, that one being the high voltage battery. Tools insulated to 1000v are required and the Bo-Peep hook will always be there to scrape my bubbling corpse from the engine bay if ever I forget my training.
It’s exciting times in the motor trade and if you’re not willing to get to grips with the world of EVs you’ll be left to rot in the scrapyard.
It’s great to feel enthusiastic about cars and even better to be part of an reemerging and reinvented technology. We’re not quite there yet with the flying cars, but at least we’ve taken a step closer towards the future of transport. Who knows where this could go…
Hopefully you’ve all found this post interesting and not too confusing. It would be great to hear your feedback so please leave a comment.
