We invented the wheel, but things didn’t stop there. It wasn’t a finished product or a job-well-done, it was the first part of a constantly evolving mechanism for transportation.
Since animals were the driving force behind wheeled transportation, we have had an unending need to make our vehicles go further, faster, and for less money or work. Eventually, we added our environment to car-improvement criteria.
Post-industrial revolution, we saw steam power and then fossil fuels, which would become the mainstay of mass-produced automation to this very day. As we started to max-out the abilities and stats of petrol and diesel cars clever people have investigated adding new parts to make engines better and thus leave our cars improved.
In the last century, we got busy – it became a priority to eke out more economy from whatever fuel was being burnt – and range-extending devices became a thing. We also wanted to know specifically: were there any simple, easy-to-implement solutions to moving vehicles that didn’t cost the earth?
Centrifugal Forces At Work
Flywheels have risen and dropped again repeatedly in the vehicle industry as a potential power source as well as a range-extender.
In principle a flywheel is a spinning disc – and they have existed in cars since the beginning. With the drivetrain of a car, it forms a connection between the engine and the gearbox (via the clutch).
But it doesn’t have its own power, it spins with the output shaft of the engine and keeps things running smoothly.
We know, however, that if you spin a sufficiently rigid and weighted disc or wheel up to a high speed, it can temporarily contain a lot of that kinetic energy already spent spinning it up, and if the bearings and all the parts are up to scratch it can be made even more efficient.
Because of the weight of the wheel spinning, its speed and the centrifugal forces conspire to keep it moving despite smaller forces working against it.
The theory is, you can get some of the energy back either as heat (as in a brake pad on a wheel) or as kinetic energy by re-coupling it with something.
You will almost definitely remember the toy cars from childhood, which after spinning up the wheels manually by running them forwards a few times; speeds off for a short distance, under the inertia, built up in a hidden mechanism. That’s a similar system for kids.
The Simple Science Behind It
The first application of this system is to store energy, from the charging-up phase, then saving it to use later, either for general-purpose – like how you would use a battery - or to just aid a vehicle for example when accelerating.
In the case of the former, we arrive at the Gyro bus.
A very interesting solution and one which could have been implemented into cars if the resources allowed; a heavy flywheel (tons of weight) on an axis is spun up by a motor onboard, powered only by an overhead wire, above a bus stop for example.
It spins up while passengers board or disembarks, and after 30-180 seconds, the bus can leave the stop - disconnecting from the overhead charger – and run-on electricity alone from the flywheel as it works backward, sending its power back to the generator.
Firstly, the top speed in town was good at between 30 and 40mph (depending on load, etc.) but a peak of between 3 or 4 miles between charges meant full power was only theoretically available continuously for 7 minutes. Possibly enough if you have charging points dispersed along the route.
Secondly – and perhaps most importantly – this design is ideal from two perspectives. It is simple in function, relatively cheap to integrate and maintain, presumably; and doesn’t use rare or toxic materials like in a standard battery.
Unfortunately, the idea hasn’t taken off as, since its use in Europe in the late 50s, it was discontinued because of the weight and low efficiency.
KERS: Kinetic Energy Recovery System
What if we made the flywheel smaller and charged it up with energy already being lost while braking in a vehicle? It would be an independent, self-contained system.
For the common-or-garden bicycle, a small flywheel charged up under braking can then supply enough energy to aid the cyclist when needed, like when starting. It could also be a nice acceleration tool, like the nitrous boost seen in The Fast And The Furious.
Introduced as a racing aid to recoup energy under braking and release it when needed as extra power, it was given the name KERS and after starting in F1 it hopped into other cars like the Audi R18 racing car and the Porsche 911 GT3 R Hybrid, using the same principles as the Gyro bus, without the overhead wires.
For the R18 E-Tron Quattro in 2013, the system effectively gives the car 4-wheel drive (Quattro) or bursts of acceleration. More recently, KERS systems in racing have superseded the flywheel with battery storage systems.
That’s not all though for the flywheel. - According to Wired, London buses will potentially also be benefitting from huge flywheels, charging up during braking and letting loose when necessary.
From KERS To Range Extension
Now onto something a little different – range in cars and hybrids.
Typically, in ICE (internal combustion engines) range was extended by using a hybrid system. For vehicles that used an electric drivetrain as the driving force, auxiliary ICE engines (including Wankel engines) were sometimes added to act as a generator to increase the drivable distance (range) if the batteries were too low. That is unlikely to be a problem with the Lucid Air EV and its quoted 500-mile range, however.
Some automakers have toyed with flywheels too, but in the end, extending the range of an EV isn’t viable with a flywheel since they can already recoup energy using an electrical KERS system straight back into the battery as the car brakes or coasts.
The humble flywheel could though still be a viable tool for light vehicles like bicycles and motorbikes, or heavy vehicles which could benefit from the acceleration boost when starting off from a standstill.
In fact, flywheels are used in many, many different applications including wind turbines and industrial machinery, so they aren’t just limited to our kids’ toy Ferraris and Lamborghinis.