When we are trying to plan for the future we may tend to rely on our current “knowledge bank” and add to that background information by being aware of any general trends within the industry. In addition, the engineer needs to be very aware of how their discipline fits into the industrial landscape and how it may react, or respond, to the ongoing changes. In many cases the action is reactive because influence is restricted, but that does not always have to be the case. If the engineer is proactive, it may be possible to influence changes and indeed preempt future designs.
The following is an opinion, formed through research of the global automotive industry and a general awareness of Electric Vehicle (EV)/autonomous driving developments.
From the outset I need to say I am certain that engineers, whether they are electrical, chemical, or mechanical, are creative individuals, addressing identified needs to meet market demands. The “status quo” is not in an engineer’s genes – they continually seek to improve. If faced with a difficult problem that hinders product development, they will work to find a viable solution. In addition to innovation, problem solving is their primary purpose in life - and at the moment they are working at quite a pace on EVs and autonomous driving.
The presentation is in three parts - first considering “EV and autonomous driving developments”, second “braking concerns of EVs” and in the third and final part “the future of friction braking – as we know it”.
Part 1 - EVs and autonomous vehicle developments as of now
Some 10 years ago I attended a committee meeting of the Division of Automotive Engineers, a subset of the Institution of Mechanical Engineers. The Chair at the time said “autonomous driving will never happen” – how wrong he was - and we can now fast forward to today.
I recall an article titled “An engineer’s introduction to electric vehicles (EVs)” which said.
“According to a forecast by International Energy Agency, the use of Electric Vehicles will grow from 3 million to 125 million by the year 2030. That is almost 41 times of what it is today, with the increasing demand of fossil fuel and problems with pollution it seems most likely to happen”.
Of course, it will happen, the above being an understatement. The inertia to changes is falling away. Autonomous vehicles are now operating successfully on the roads. There are some issues with testing, but we need only review recalls on established designs to see that “glitches” are part of the DNA of the automotive industry – and braking is no exception to recalls. Not convinced – search “Braking Recalls” – you will realise that friction brakes have their problems. Such EV development problems are the lifeblood of cynics who magnify these so they can present them as the reasons why we should not follow such a path, inferring they are simply not safe. It is easy to hide from such advances in technology but there is a need for all of us to evaluate the rate of developments over the last few years and accept that changes are coming. We all appreciate that such developments are already demonstrating an exponential increase - and suppliers will need to adapt sooner than they would like.
To measure the advances you may search for “autonomous patent applications” over the last few years – and note the rate of increase. If there are any doubts about such advances you may review NIO’s sports car (autonomous) and Tesla, the latter leading the market in EV development, and production. Indeed, look at the marketing structure NIO are introducing into Norway – including servicing and battery exchanges. Companies and organisations making use of commercial vehicles are commissioning electric vehicles now – by the thousand. Typically, Amazon’s involvement with EV start-up Rivian, delivery businesses and state-owned services are “buying-in” to EVs. Also, see VW’s budget for electric vehicle development and the number of new models they intend to launch by 2030. In addition, review Jaguar Land Rover, Ford, and GM near distance plans for EVs. The latter two to introduce 33 new EV models to their existing ranges.
Geely Automobile Holdings are to make the Volvo electric cars in China and intend to launch 15 “new energy vehicles” in China. Indeed, the Volvo “Polestar” electric vehicle is intended to embrace a subscription service – a car on demand without ownership – the Uber model.
In 2018 it was reported that Xi Jinping (Chinese President) said,
“We know that incumbent automakers around the world will resist changing to clean transport systems for years to come. So, with that head start, we will require Chinese companies to build all-electric vehicles to first clean up the air in our cities. Then, with leadership in EV technology established, we will export to the world, where we will dominate because of our superior costs.”
In 2020 China produced 93% of all EVs made in APAC countries.
Regenerative braking can absorb 50 to 80% of all braking, around 70% being an accepted value. The introduction necessitates no extra weight - only software. Of course, such rates depend on battery condition, but battery management may ensure such capacity is always available. Once such developments are in-place (and that will not be long) friction braking will begin to experience its demise.
Part 2 - Braking Concerns of Electric Vehicles
Friction braking has not changed significantly over the years – only peripherals such as ABS being added to the basic operating principle.
The main questions which arise from the introduction of EVs are:
Who will trigger the changes to braking technology?
Is the friction braking industry behind the curve?
Can the friction braking industry be proactive, innovative and lead the technological advances - lead the curve, or will they be become reactive to the demands of the OEMs?
Are they capable of a significant mindset change as the electric and autonomous vehicles develop?
Is the friction brake, as we know it, on cars and trucks nearing the end of its useful life?
Who will first see the effects of changes?
At the moment we are not driving the future – it is out of our hands as we are not placed within the supply chain at a sufficiently high level – and we need to recognise that fact and partner with appropriate visionaries. There are also alternative suppliers that can “step-in” to fill any void if first choice is not suitable. We must also ask whether it is feasible that the new autonomous driving technologies could even reduce the need for emergency stops? My instinct is to say “no”, but then I add, “not at the moment”, and add further, “maybe later this year”. Braking efficiency in governed by the tyre/road adhesion and not by the brake. Without downforce, the possible deceleration will be in the region of 0.8g – regardless of the system used.
If I may indulge in some analysis, I present some figures for consideration.
A vehicle has a mass of 2000kg.
Deceleration 120kph (33.33m/s) to zero
Tyre/road adhesion level of 0.8.
Braking/deceleration time is 4.25s
Distance travelled is 71m.
Using the above it is calculated that a braking force of 15696N, 1.111MJ of energy absorbed and power of 262kW as being necessary to decelerate the vehicle from top speed to zero.
For interest, the NIO EP9 sports car has 4 motors each of 250kW of power and has negotiated the Nürburgring racetrack autonomously.
Consecutive Braking: Regenerative followed by friction braking.
When regenerative braking is initiated the electric motors act as generators. Regeneration may absorb most of the energy (say 70%) and then friction brakes are currently needed to bring the vehicle to a stop. If that is accepted as a premise, then the above energy to be absorbed by the friction brake reduces to 0.333MJ and at that point the speed decreases to 18.26m/s (66kph). Braking time for 0.8g deceleration is now 2.33s giving power absorbed by friction brakes 143kW.
The regenerative braking is activated for 1.92s, during which 405kW of power is absorbed. This results in 540A current flow if using 750V batteries. Friction braking is then used to absorb the remaining energy.
Concurrent Braking: Regenerative at the same time as friction braking
Time for both braking events remains at 4.25s giving regenerative power absorbed 183kW and friction braking power 78kW.
Clearly there will be an optimum “blending” that proves most beneficial to both systems.
Operational Concerns
ABS is not an issue and can be employed in a similar way to hydraulic brakes. In addition, through vector control, the acceleration and braking can add significantly to ESP operation. If there is a need to reduce current flow but still use 100% adhesion utilisation, then possibly integrate a flywheel into the driveline – and then control the current flow into the batteries? Remember, we are engineers, we are problem solvers - even though some of our problems emanate from our own innovations. That is embedded in the development process and to be expected.
Regarding charging points. Cable television was quick to uproot roads and walkways to connect homes. Is it imagined that recharge supplies will be restricted to limited areas, or streets will be lined with such stations? Of course there will always be a need for friction brakes – but there will be significantly fewer suppliers than exist at the moment and fewer in the supply chain. Those that remain will be reduced in size.
Part 3 - A consider view of the future of friction braking
An analogy: The introduction of EVs will be like a flood around a mountain – the mountain being the braking community supply chain pyramid. It will start at the bottom of the mountain, impacting the initial players early. It will progressively rise as the developments increase and during that rise will absorb more of the chain, but at a reduced rate as the industry reduces in size. Without change the lower supply chain will flounder in the evolutionary changes and the top tier will have to adjust accordingly.
Although there are a vast number of units on the road at the moment, I firmly believe user demand will not increase as predicted nor remain the same, as some believe. That opinion is formulated because the “work from home” will become more commonplace and the current environmental concerns begin to bite. It is cheaper by around 30% to run an EV rather than an IC vehicle. Health also blights the IC vehicle in many ways. A recent survey in the UK says 1 in 19 deaths are the result of air pollution.
The links of brake dust to health issues will increase as research concentrates on such problems. The cost to continuously reduce harmful emissions from brakes may far outweigh the benefits of developing new friction materials. NVH is a significant outlay for the friction braking industry and that will reduce as EVs increase in number, and friction brakes decline in usage due to regenerative braking. As such it is anticipated that noise fix shim companies will be the first to see the effects. Replacement pads will reduce as usage falls, eventually resulting in pad replacement being non-existent. The second to feel the effects will be backplate and friction material suppliers followed by conventional hydraulic brake design unless the latter changes to meet technological demands. The disposal of oil is not good when the vehicle reaches the end of its life, and this should be a consideration.
Consider the following:
In 2018 the first self-driving cars appeared on public roads.
Around now, the complete industry will start to be disrupted. You may already be experiencing it.
The populace will not want to own a car anymore. You will call a car with your phone; it will show up at your location and drive you to your destination. Elon Musk refers to this concept as the Robotaxi.
You will not need to park it; you only pay for the driven distance and can be productive while driving.
Our youngsters will never get a driver's license and will never own a car.
It will change the cities because we will need 90-95% fewer cars. We can transform former parking space into parks.
1.2 million people die each year in car accidents worldwide. We now have one accident every 100,000 km, with autonomous driving that will drop to one accident in 10 million km. That will save a million lives each year.
In conclusion:
I don’t really believe it will be a good move to ignore the developments of electric or autonomous vehicles – the developments will be faster than anybody anticipates at the moment.
The braking industry needs to be looking towards bringing a vehicle to a stop using technologies other than a friction brake – if they don’t seek alternative systems, somebody else will.
The time-base for such developments is vague and driven by stakeholders on both sides of the argument. The industry needs to be impartial.
The industry would do well to monitor ongoing developments and “think outside the box” ……. and start partnering.
My suggestion is that suppliers should not accept the status quo and should continue to increase their awareness of EV/autonomous developments, so keeping ahead of the curve. The OEMs are partnering to reduce costs of development – the friction brake industry should do the same.
Professor John Fieldhouse is currently an advisor to industry and provider of short courses regarding braking and NVH issues. He is a National Teaching Fellow and has for many years been a visiting professor at The University of Leeds - teaching chassis systems and vehicle performance. He holds a BSc from the University of Leeds and gained a PhD at the University of Huddersfield where he was awarded professorial status. John is a member of and an instructor in Brake Academy.
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