Synopsis: Vehicle controls are shaped by history but are still slowly evolving.
Vehicle controls continue to evolve, often because the things in a vehicle that can require control also evolve. This is a look at new EV specific question of controlling regen and the trend of one-pedal-driving as well as some new other new vehicle control systems.
EVs are relatively new, and while EVs do remove several controls such as gears and clutches, there is a new key new thing than can be controlled: the level of regenerative braking or “regen”.
EVs can either give the driver exposure to controlling “regen” through high levels of “lift-off” regen, or by fully integrated into regen braking into the braking system, allow the computer to control regen by automatically applying regen braking in place of using the friction brakes whenever possible, removing any need for the driver to be conscious of “regen”. This second approach can lead to the common mistake in car reviews:
- Mistake: “I don’t get much regen when I lift-off, therefore I assume this vehicle has low regen”.
What many don’t consider, is that there are two different systems for controlling regen, and the regen available from lift-off is almost never the full regen an EV can provide, and with most vehicles, nor is it the full regen provided independently of the friction brakes. Full regen on a vehicle with really strong regen capability will normally never occur without pressing the brake pedal, as few people want to experience the force of an emergency stop just from lift-off.
For vehicles like the Porsche Taycan, with regen that can be over 260kW, providing that full level of regen through “lift-off” alone would be comprise driving too much for Porsche engineers, which leaves them believing brake-pedal-regen is the only practical solution.
At the other extreme, some vehicles most notably including Tesla vehicles, only offer “lift-off” regen, which limits the maximum regen control available to the driver and necessitates a high “lift-off-regen” setting to access efficiency, and trades more reliable access to efficient driving for a new fun experience.
While which system will win in the end is unclear, it is clear there will be a lot of confusion over “lift-off regen” vs “brake pedal regen” in the interim.
Using high levels of lift-off-regen requires adopting an EV specific driving style which is also highly suited to also adopting “one-pedal-driving”, where automatic activation of friction brakes is used to supplement regen braking.
Tesla is one to the two world leading EV producers, and as the dominant EV supplier in many countries including the highly influential USA market, some assume how Tesla does things is normal for EVs, but it turns out that the Tesla “no part is the best part” approach simply means Tesla does things differently!
The evolution of driving controls will come from many sources and while many good ideas do come from Tesla, but they are not the only innovators, and were even late to introduce “one-pedal-driving” years after Nissan and BMW.
Tesla has pioneered shifting all driver display information to the entertainment screen, reliance on only “lift-off regen” systems, removal of radar and sonar sensor and cars making fart noises, and Telsa has been a pioneer in the introduction of yokes for steering. Not always practical, but usually fun, and Tesla is always pushing the boundaries of how vehicles are controlled.
But not all new control need be adopted by everyone. Just as only Tesla drivers can need to adapt to using the entertainment screen to see their current speed, they have also learned to adapt to lift-of-regen being the only regen available. Brake pedal based regen is at least equally efficient, does not require adapting to a new way of driving, and may address some safely concerns, but is it as much fun?
The same exploration of alternative control systems will continue as AI, the transition to EVs and other factors change vehicles and how we control them.
We have entered an era where people can configure controls of a vehicle to suit themselves, and not everyone makes the same choices.
Which choice is the most enjoyable is personal and this webpaper can’t substitute for people making their own decision there, but it may help break through the myths and misunderstandings about efficiency implications and how systems work, for regen braking, one-pedal-driving, and other emerging new vehicle control options.
Myths and misunderstandings: Regen in reality is quite different.
One pedal driving in enabled by friction brakes, not regen!
There is a very pervasive myth that one pedal driving is a product of the high regen available in EVs, when the reality is, it is the use of friction brakes to stop the vehicle than enables one pedal driving.
Further, in any EV, even those with low lift-off regen, there is absolutely zero difference between one pedal driving and using the brake pedal beyond the driver’s use of their foot!
In one pedal driving, the actual stopping always comes from the EV automatically applying the friction brakes, which does not harm efficiency.
To understand this, consider what Tesla changed in order to introduce one-pedal-driving: it was the introduction of stopping mode for the friction brakes that made the difference between just high regen and one pedal driving.
Prior Telsa introducing friction brake stopping mode, it was clear regen becomes ineffective at around 3 mph. Do people really think Tesla was turning-off regen braking when the vehicle slows unless “stopping-mode” was set to hold?
The key word in how regen-braking works is “regenerative“. The braking power comes from the battery absorbing the electrical energy generated by using the motor as a generator, and the slower the vehicle, the less electricity can be generated.
The faster the vehicle is moving, the better regen works, and the slower the vehicle the worse it works, down to near zero speed, when there is zero regen. There is a minimum speed at which regen works, preventing regen making a vehicle actually stop. The actual stopping requires friction brakes, but as the friction brakes only need to take over when the vehicle is already at low speed, the wear on the brakes has already been minimised and there is no significant reduction in efficiency.
The efficiency of regen comes from the fact that there is electrical power being generated. Regen braking only functions when the vehicle has enough kinetic energy to forcibly turn the motor to generate electricity.
The good news is that at the speeds when regen stops working, friction braking works extremely well. These are the types of speeds when friction brakes work so well that new drivers end up stopping being stopped before they expect, as less friction brake force is needed when nearly stopped.
At these low speeds, there too little energy to harvest, but also too little energy to worry about being lost, or to cause wear on the friction brakes. There is no real cost to the fact that friction brakes come into play for stopping, but it can still be worth understanding.
Regenerative braking cannot keep the vehicle stationary, as it is not practical to be generating electricity from a stationary vehicle!
An electric motor can be used to hold a vehicle stationary, but doing so consumes electricity and would eventually flatten the battery and is definitely not regen braking, nor a sensible idea. Again, friction brakes are the best solution and use no energy keeping the vehicle stopped.
ICE vehicles could offer one pedal driving if they choose to do so.
Even though lift-off-regen normally will not unleash the full potential of EV regen, it provides enough “engine braking” such that friction brakes will only need to take over at quite low speeds. However, the principle of first use engine braking to slow the vehicle and then apply friction brakes to stop, could also be applied in and ICEV with an automatic transmission.
“Lift-off-regen” is no indicator of actual regen strength.
Many “road-tests” make the mistake of assuming the strength of “lift-off regen” reveals the amount of regen a vehicle can which is completely false. Consider this from a review of the Porsche Taycan, which offers neither the one-pedal-driving, nor high “lift-off-regen” of the Tesla Model 3, yet has according to this review by experienced EV journalist Tom Moloughney, has at 265kW of regen power over 3x the regen of the Tesla Model 3:
Porsche’s implementation of the regenerative braking system for the Taycan is different than the systems on other electric vehicles available today. It’s both very strong and very weak at the same time, it just depends on how you look at it.We Evaluate Porsche Taycan’s Unique Regenerative Braking System
Porsche wanted to do two things when they were designing the Taycan’s regenerative braking system.
First, they wanted to recuperate as much energy as possible, and they believe they achieved that goal. Porsche engineers have said that as much as 90% of the Taycan’s braking will, on average, be achieved through regenerative braking. The Taycan is capable of generating up to 265 kW into the battery pack.
That’s accomplished by adding the front motor’s 175 kW regeneration capability, and the 90 kW recuperated by the rear motor. To put the Taycan’s 265 kW regenerative braking potential into perspective, the Tesla Model 3 can generate a maximum of 77 kW, less than 1/3 of what the Taycan is capable of pumping back into the battery.
Secondly, they wanted to make sure the Taycan would be well suited for high-speed driving on the autobahn, as well as for the track. Strong lift-off regeneration can be cumbersome when the vehicle is being driven at high speeds, and it can cost you lap time when you’re running on a track.
In reality, no one would ever want 265kW of “lift-off-regen” delivering its full high performance braking levels pressing occupants into their seat belts in response to the driver simply lifting their foot from the gas/power pedal! Telsa restricting their highest level of lift-off-regen to 77kW is being practical, but it also highlights how lift-off-regen is by its very nature limited. I suspect even though Telsa vehicles do not have brake by wire, it is possible they may increase regen beyond that 77kW level when the brake pedal is pressed.
This case where designers of a vehicle to choose not provide high lift-off-regen, but do provide a higher level of brake-pedal-regen and in many case when needed higher than the regen people experience on lift-off with a Tesla, is not something unique to either Porsche or the Volkswagen group, as can be seen in this video another EV “personality” known as “Tesla Tom” first tests how brake-pedal-regen is more powerful than “lift-off-regen” in vehicles not branded “Tesla” as those by EV juggernaut BYD.
Lift off regen is not the only regen, and with most EVs not the powerful regen.
Even experienced EV reviewer Tom Moloughney, after having previously seen first hand brake-pedal-regen in a Porsche, did not automatically click that he was seeing it again in the ID.7 which is from the Porsche parent company Volkswagen:
If the driver prefers stronger regenerative braking force, they can select the B driving mode which increases the regen strength considerably, but not enough for a true one-pedal driving experience.InsideEVs: 2025 Volkswagen ID.7 First Drive: The Stealth Premium EV Sedan Choice (at best poor wording)
These words give the impression that the reviewer, again the very knowledgeable Tom Moloughney, understand neither brake-pedal-regen, nor that it is friction braking, not lift-off-regen, which is required to enable one-pedal-driving. The words do not make clear that both driving mode settings of the ID.7 provide the same regen, and that the only change between settings is how the controls work with ultimate regen level in all cases resulting only from brake-pedal-regen. One pedal driving is not offered because VW decided that automatically applying friction brakes as required for one-pedal driving is not desirable.
Even to an experienced journalist, the concept of a vehicle having high-regen, but that regen not being evident when “lifting-off” was radical. Tom Moloughney missed it with the VW and vehicles other than the Porsche, but did understand the perspective explained by Porsche unlike this other reviewer who mistakenly assumed that the brake pedal will always activate friction brakes even with EVs (although I suspect that reviewer also now understands having now worked with others, but videos are not easy to edit).
This myth that “lift-off-regen” is the only regen, perpetuated by the lack of understanding of brake-by-wire is the biggest myth around regen and one-pedal-driving.
One-pedal-driving can be less efficient than more conventional driving.
There are so many myths around “high-regen” and one-pedal-driving but the most culminated in the belief that one-pedal-driving is some holy grail of efficient EV driving. It isn’t. Road & Track explain in this article: One-Pedal Driving Isn’t Necessarily the Most Efficient Way of Driving an EV.
It is not that one-pedal-driving is inefficient, just that it can be slightly less efficient than more conventional “power-pedal” response and using the brake-pedal. One-pedal-driving can still be satisfying, and there is no reason to avoid its use, but neither is there any reason to feel it is in some way necessary.
Consider the following other myths tacked by:
- Regen braking is not the main reason EVs are efficient.
- EVs are not less efficient on the highway because there is less chance to use regen.
- Regen braking does not bring vehicles to a complete stop.
- No, regen settings do not change available regen.
These myths all contribute to the myth of one-pedal-driving being necessary rather than just fun.
Vehicles identified as having “low regen”, often have very powerful regen.
No, regen settings do not change available regen.
OK, Tesla is at least partially an exception due to the lack of brake-by-wire, but even on a Tesla, full regen is always available when using “auto-pilot” or any other automated driving system.
Regen braking is not the main reason EVs are efficient.
In hybrid vehicles, regen braking plays a more significant role, but even in hybrids just the use of an electric motor to aid acceleration reduced fuel consumption and allows use of a smaller less powerful gasoline engine, further improving fuel consumption, and regenerative braking is only one part of the improved efficiency.
With an EV, the main gain in efficiency is elimination combustion, which converts the energy in fuel into heat, and most of the heat is lost through the radiator and engine cooling system and the exhaust with only around 25% of the heat typically able to be converted into moving the vehicle.
Regen is still a form of braking and is not more efficient driving without using the brakes at all.
All use of any form of braking is results in wasted energy. Slowing down reduces kinetic energy. Regen can save around and then later return as much as 70% of the kinetic energy, while friction braking saves 0%, but still around 30% of the energy lost.
EVs are not less efficient on the highway because there is less chance to use regen.
EVs are actually more efficient on the highway than they are in urban driving, and EVs are less efficient when they need to use regen than when no brakes are required. The reason EVs use consume more energy on the highway, is because going faster requires more energy. Air resistance increases with the square of speed, so for 2x the speed, the air resistance increases by 4x!
Familiarity with ICE vehicles creates a distorted perspective.
How can ICE vehicles have low consumption at higher speeds?
Internal combustion engines mask the impact of speed on the need for energy because the provide increased efficiency as they are required to work harder at greater speed. Unlike an electric drive train, where efficiency is high at all times, the efficiency of an internal combustion engine can vary from around 5% at very low loads, to 30% and in some cases higher at higher loads.
So, with an ICEV the effect of driving faster is in part compensated for by the energy improving in efficiency. The result is that factors that have a big impact on EV efficiency, matter less with an ICEV. The problem for ICE vehicles is that operating at low loads is problematic, which means stepping up to a more powerful internal combustion engine, can make a vehicle less efficient when driven at normal speeds.
Regen braking nis not what makes EVs efficient. EVs, like other vehicles, are most efficient when it is possible to avoid all braking.
Regen braking does not spin the electric motors backwards!
I have seen this myth written on several web pages and repeated in online videos.
The motor of an EV is connected to the wheels. When the motor spins backwards, it makes the vehicle moves backwards. This is called reverse! The motor cannot spin backwards when the vehicle is moving forward.
Further, the use of the power of the motor to push against movement would require using energy, while regen braking is generating energy. It is possible to power the motor to slow the vehicle, but this is not regen. Regen makes the motor difficult to rotate as the motor is configured so that rotation will generate electricity, but there is no “spinning the motor backwards” other than when driving it reverse, which uses power in the same manner as does driving forwards.
As explained in more detail below, the motor, when used as a generator, resists being turned, and the vehicle forcing the motor to be rotated generates electricity.
A review of main vehicle controls.
Main controls: Background on the functions and naming.
The evolution of controls is on path to “self-driving” where the driver need only indicate a destination, but there are times, such as when off-road, when it is about the journey not the destination, so being able to directly control the journey will likely remain as a requirement, even if in many cases it does cease to be required. The basic controls for controlling a moving vehicle from a logic perspective are:
- Steering direction: Currently almost always via a “steering wheel”, although the tiller and yoke are alternatives.
- Power level: Now controlled by a Go/Power pedal, also known as an “accelerator”, “gas pedal” or “throttle”, but historically often controlled by hand.
- Brakes: Controlling what level of braking, if any, is to be applied to bring the vehicle to a halt. Currently the “brake pedal”, although handbrakes are also still in use, as directly activating a brake mechanism is currently the normal way to stop.
This topic focus on the main controls, but it is important to note there are far more are supplementary controls including:
- Mode: Forward, reverse, parked etc., less critical and more varied in detail as not normally requires when the vehicle is in motion.
- Supplementary controls such as lights, windscreen wipers demisting and temperature controls.
- Gears: Mostly reduced to a mode function with EVs.
- Clutch: Mostly now with EVs confined to history along with such controls of the past such as the choke.
- Ride height, tractions modes etc.
Of the main controls, moving to EVs does not directly change what is needed in terms of how steering operates. Of the three main controls of steering, power and brakes, it is steering that is least changed with the move to EVs. The only change is that use of electric power steering becomes even more compelling, but many ICE vehicles had already moved from hydraulic to electrical power steering.
It is the control I describe as “Power” which has most clearly makes previous names anachronistic with EVs as although it has always been a control over the power source, in ICE vehicles it began as a throttle directly controlling the fuel air mix of the combustion engine. Not only does the “power” control of an EV function differently mechanically, but it can also be configured to also on “lift-off” to provide different levels of “regen” or regenerative braking and, even in some cases, friction braking.
While I use the name or terminology “power pedal” for EVs, there is no widespread agreement on a new name despite the traditional names all having one of these problems:
- Throttle: became technically obsolete with the move to fuel injection and although even when it was the most accurate description it had started wane in use due perhaps to being too technical.
- Gas pedal: Only logical when the fuel is “gasoline”, and rarely popular in countries such as the UK where the world “petrol” is used in place of “gas” or “gasoline”.
- Accelerator: The control is still needed even to maintain constant speed, and unlike the “brakes” which is a control only needed when deceleration is required, this control is still needed even acceleration is not required.
However, while the name needs no change, in fact the biggest change mechanically is with the brake pedal. While with ICEVs, braking via the brake pedal is always friction braking with the conversion of the energy of motion into heat, with most EVs, the brake pedal also activates regen braking. With ICEVs the use of engine braking quite was normally quite limited, but with EVs the motor(s) and battery can form an integral part of the braking system working together to convert the energy of motion into electrical energy for storage and then later use, and the amount of braking available is sufficient to significantly reduce the use of friction brakes. However, whether the effect of pressing the pedal is regen braking or friction braking, the pedal control is still controlling braking, just as with an ICEV.
ICE Vehicle controls: the historical starting point.
As the control of todays’ EVs are evolutions of the controls of Internal Combustion Engine Vehicles, it is how controls operated with ICEVs that is the starting point for vehicle controls of EVs.
All controls began as ways to mechanically operate components used to achieve what the driver wanted the vehicle to do.
Early automobiles were steered by a tiller, but the steering wheel soon took over, and although some vehicles are experimenting with yokes, there is no change brought about by EVs that necessitates changing steering controls. While controls may change, it is not really EVs bringing that change.
Controls for gears have been changed a lot over the years, but as ICE vehicles had already introduced “shift by wire” and clutch pedal are already rare the “gear selector” control of EVs already is similar to use to that of an ICE vehicle even though what is actually happening is very different.
The main remaining controls are the two remaining pedals, which have the functions of “Brake” and “Power level”, and these are particularly interesting as because these are what is most different with an ICEV and an EV.
In an ICEV, the “Brake” pedal controls only the friction brakes. Early controls for brakes began as a lever, and as brakes became more powerful the lever did need to be rather long in order to provide leverage needed by the operator. However, by 1918 when hydraulic assisted brakes first emerged, the control had already become a pedal, thus enabling leg strength to be used, and despite changes to the details and hydraulic assistance being added, and later brake by wire systems, even in EVs the brake pedal remains a control that can physically control a friction brake system. Even with brake-by-wire, in the event of failure, the system becomes a mechanical control of hydraulic pressure.
Next is the “power” control.
I use the label “GO/power-pedal” instead of any of the traditional labels of “throttle”, “gas pedal” or “accelerator”, because there is no throttle or “gas” in an EV and the pedal does need to pressed even to maintain a constant speed without acceleration.
In early vehicles such as the Model T ford was a steering column mounted hand control. The pedal control appeared in vehicles like the 1910 Peerless Model 27 and the Cadilac Model 30 which also introduced the electric starter motor, although Wikipedia states Wilson-Pitcher in introduced a foot override for the hand throttle1900 that claim may not be quite right given the company was not formed until 1901, so while one sample car may have been built at that time, it is not clear what was actually introduced in production.
Vehicles with a hand throttle continued for a long time, still being present in off-road vehicles like the Mitsubishi Pajero in 1981 with the hand throttle functioning as form of cruise control.
Although now more commonly known as the “gas pedal” or “accelerator”, it was originally called the throttle or “throttle control”, because it controlled a flap that closed off the pipe of fuel-air mix (video here) to be delivered to the engine. Accelerator ‘flat to the floor’ being the throttle ‘fully open’ to allow maximum fuel air mix into the engine. How far the pedal is pressed mechanically controlled the flap allow fuel air mix into the engine.
Control by wire: the ultimate goal?
Vehicle controls are all moving to operation ‘by wire’, which means instead of being physically operated by a by a mechanical connection to the control manipulated by the driver, instead the driver is operating a controller that provides input to a computer, and it is the computer that activates systems to physically controlled the vehicle.
The ultimate goal of ‘by wire’ controls would be to achieve the simplest and most intuitive controls possible that enable the driver to communicate what they want the vehicle to do.
Steering by wire: Not yet a big thing.
Although autonomous driving requires the computer to be able to control the steering, in most vehicles steering done by the computer is still applying force to the same steering controls used by the driver, rather than a true steer by wire system. Lexus is introducing steer by wire, but at time of writing this is still experimental technology, and Tesla has introduced yokes, but curiously so far (2023) without steer by wire.
“Power by wire” required with an EV, and already in use in many modern ICEVs.
The “GO/power pedal” of a modern ICE vehicle with computer controlled electronic fuel injection is no longer mechanical a ‘throttle’ control as now a computer controls the fuel air mix injected into the engine.
On an EV, a computer controls motor speed, which means that the “GO/power pedal” on an EV is also a “by wire” control to computer and the same type of control as an on a modern ICE vehicle.
Where things get more complex, is that historically the “GO/Power pedal” by controlling fuel to the engine, inherently controlled engine braking, as engine braking is an inherent property of an internal combustion engine that happens as a result of reducing fuel supply.
This has meant that traditionally the “Go/power-pedal” has to some extent been a “POWER-AND-BRAKE-pedal”.
Electric motors do not have any inherent “engine braking” and the closest EV equivalent to internal combustion engine braking, is regenerative braking aka regen, but as regen is not an inherent characteristic of an electric motor and can produce far stronger and more effective braking than engine braking of an internal combustion engine, the question arises as to whether regen should be controlled by the “Power-pedal” or if it would be more logical for this to be controlled by the “Brake pedal”.
Not everyone fully agrees on the answer, but all EV so far do at least offer settings with some regen control from the “GO/power-pedal” and all major brands other than Tesla also provide regen control via the “Brake-pedal”.
“Brake-by-wire”: For almost all EVs, but so far, excluding Tesla.
Note: brake-by-wire is also often labelled “blended braking”, but I have avoided this label as Tesla also uses “blended braking” to describe their use of a blend of regenerative and friction braking to implement one pedal driving, which is quite different than the normal use of the term “blended braking” to describe what happens when the brake pedal is pressed.
On most EVs the pedal no longer directly controls the friction brakes, but instead sends a signal to the computer that the driver wants some “stopping force” applied and how that is achieved is determined by the computer.
Not all EVs, mainly because Tesla, with a dedication to minimalism and firm belief that the self-driving future is practically already here, eschews using brake-by-wire.
I am unsure exactly when brake-by-wire was first introduced. From this very sound article from Road &Track it was already in use with the first modern EV, the GM EV1:
GM’s infamous EV1 used regenerative braking to improve range, which was controlled by what we now refer to as a “blended” brake pedal. When the driver stepped on the brake pedal in an EV1, the car blended both friction braking and motor regeneration with an extremely complex brake-by-wire system. A press release from back in the day noted that at low speeds, regeneration could handle 95 percent of the car’s deceleration needs.Road &Track: One-Pedal Driving Isn’t Necessarily the Most Efficient Way of Driving an EV
Which means “brake-by-wire” was in production from 1996 with the GM EV1 if not earlier, for the purpose of allowing the “brake pedal” to control regenerative braking.
In principle, brake by wire means both “Go/Power pedal” and “Brake pedal” have become simply inputs to a computer, what each pedal controls is entirely determined by software. Either pedal can be used to control the motors, regenerative braking, friction brakes, or even steering depending on software. In practice, the big difference between these two pedals is that the “Brake pedal” is designed to directly mechanically control the friction brakes in the event of a system failure.
The added complexity is the requirement for creating a “by wire” control for braking requires a system that switches automatically to a mechanical control if the computer fails. It is the provision of this “fail safe” that makes “brake-by-wire” more complex than conventional brake pedals, and this makes the brake pedal still physically different in how it operates compared to the GO/Power pedal.
As already mentioned, a hydraulic system to assist with applying force to the brakes was introduced as early 1918 as the system and the force required to push the brake otherwise is too great.
However, the hydraulic system is still not “by wire” as pressing the pedal still directly sends hydraulic pressure to apply force an activate the brakes, so even if the power assistance fails, a person can push as hard as they can, and the car will still stop. If the system fails the assistance is lost, but not the brakes.
For ‘brake by wire’, there needs to be a system that allows the physical pedal to still operate the frictions brakes if all else fails. The problem is, with an EV, mostly the friction brakes are not wanted even when the brake pedal is pressed. The solution is that the hydraulics have valve, kept open by the computer, that automatically closes unless instructed by the computer to stay open. When the value is closed, the brakes are in manual mode as with an ICEV, but normally, the computer handles all braking, and only uses friction brakes when necessary.
Regen: The two systems.
Regen system one: Lift off regen, the regen you can feel.
Operation with this implementation system mimics the engine braking of an ICE vehicle, activating regen when the driver eases of the gas/power-pedal. Since the regenerative braking of an electric motor and battery is typically capable of creating a far stronger braking effect than that normally experienced with a combustion engine, most vehicles either, provide only limited rather than full power regenerative braking in response to gas/power-pedal lift-off, or provide an option to provide only limited regenerative braking in response to lift-off.
Regen system two: Brake-by-wire brake pedal regen, the less intrusive regen.
In any EV equipped with brake-by-wire, the full regen potential is available via the brake pedal is pressed, which means whenever the vehicle can use regen and recover electricity, it will. There is no more need to adopt a new driving style to drive efficiently in most EVs than there is for driving a Toyota Prius.
Both “power-pedal” and “brake-pedal” of an EV can be used exactly as with an ICE vehicle, and unless the vehicle is a Tesla, the result will be at least as efficient as any other configuration or driving style.
There is a myth that a very high-regen setting, or even one-pedal-driving, is necessary to drive an EV efficiently, but if the EV is not a Tesla, then as explained in this article from Road & Track: One-Pedal Driving Isn’t Necessarily the Most Efficient Way of Driving an EV.
In the USA and many other markets, Tesla has been the dominant EV brand to such an extent than some people thing of all EVs as Tesla vehicles, and there can be an assumption all EVs are like Teslas. The truth is that Teslas are EVs with quirks and differences from other EVs, and while the Tesla way has a lot of very ardent fans, the Tesla way is not the only way.
Regen level settings: Only as selection for the level of “lift-off-regen”?
Almost all EVs offer some form of “regen level” adjustment. Even Tesla, who initially offered a “low” regen setting, removed it in a late 2020 software update, but then it was reinstated in an April/May 2023 update.
These “regen level adjustments” are about driver preferences, not some magic that needs to be learnt to drive an EV efficiently. These settings are fine tweaks that as Jack from Fully Charged says, are to some extent for “massive EV Nerds“.
Yes, Tesla vehicles are different, and the lack of brake-by-wire means that, in in a Tesla, changing the regen setting to “low” setting is reducing the amount of regenerative braking available with the impact discussed below, but driving a Tesla on “normal”(full) regen is discussed here and is similar to other vehicles.
That is all for the different, Tesla style regen settings, and the rest of this section applies to other EVs which do have brake-by-wire.
Lift-off-regen: With brake-by-wire vehicles, “regen” settings do affect “lift-off-regen” settings, but do not change the total amount of regen in use, as most regen is from brake-pedal-regen.
What is often misunderstood, is that the full regen capability of the vehicle will always be still be available via the “brake-pedal“. In any vehicle with brake-by-wire, the total regen available is unchanged by regen settings, and all that changes is how the vehicle behaves in response to driver input via the “power-pedal“. Some brands like to try to even avoid the name “regen” with the setting in order to avoid confusion.
Lift-off-regen is the regen the driver notices, while in contrast well configured “brake-pedal-regen” feels no different to conventional friction brakes and recovers energy in the most efficient way possible without the driver needing to adjust how they drive. The only accurate way to observe total regen level is via a readout of power usage which indicates negative level during regen.
Many brands even provide dedicated controls to dynamically change the response of “lift-off-regen” regen level”, through controls such as steering wheel mounted paddles. The settings in some vehicles can become complex, but in the end the settings are just tweaking response from the pedals to match driver preferences, and all brands keep simple settings for maximum efficiency, because that results in best result on statutory tests that will determine the official range and efficiency.
The bottom line is that default settings will normally be as efficient as any other setting and offer and convenient driving experience enables a driver to drive with optimum efficiency.
The Tesla difference: brake-by-wire vs minimalism & self-driving.
While most other EV brands adapt brake-by-wire as necessary for optimal EV driving efficiency and allowing EVs to be driven efficiently without adopting new driving styles, so far, Tesla vehicles, at least since the Modes S if not before, do not include brake-by-wire.
Omitting systems other brands include a Tesla theme. In the Models 3 and Y, Tesla also omits a display in front of the driver for speed and other information, which again almost every manufacturer other than Tesla provides. Recently Tesla stopped fitting radar sensors and sonar parking sensors. The idea is that central display can also double as the driver display, cameras also perform the roles of sonar and radar, and the “gas/power pedal” can also control all but emergency braking.
Are the driver pedals beginning to matter less anyway? Already, significant distances are driven using adaptive cruise control systems without any use of the brake pedal. As these systems are computer controlled, they are already able prioritise regenerative braking and deliver optimal efficiency. Tesla already offers “full-self-driving” and is clearly dedicated to a future where almost all driving with need neither a driver display nor driver pedals for stop or go.
So far, just as Tesla drivers seem happy to accept adapting to having no driver display, and many prefer the adjustment to driving style required to drive an EV efficiently without the aid brake-by-wire. and enjoy one-pedal-driving.
Tesla loves minimalism.
That applies to not only cabin ambiance, but also technical equipment, and it is not always even noticeable.
Step into a Tesla model 3, and you can see there is no display in front of the driver. It is obvious.
But not all the things Tesla omits are obvious. If you drive a Tesla, it is not obvious that the driving is different because other EVs have brake-by-wire.
Tesla is also removing RADAR and ultrasonic parking sensors from its cars, but as there are already also cameras, with the rights software it is expected drivers will not experience any difference. What Tesla does is different, and even if it can make driving a Tesla different, it does not make Tesla vehicles necessarily better or worse.
To quote Elon Musk:
Over and over, the tendency is to complicate things. And I have another thing which is, the best part is no part. The best process is no process. It weighs nothing, costs nothing, can’t go wrong. So, as obvious as that sounds, the best part is no part.
Tesla likes to leave out what it can, and while sometimes the driver must adjust, many drivers see it as preferable in order to experience minimalism.
So far, I am not aware of any other EV without brake by wire. From the launch the Model S, at least until the current date of April 2023, all Tesla vehicles have not been equipped with brake-by-wire. This follows the “no part” philosophy, avoids having one more thing that could fail, some believe delivers a better brake pedal feel.
Regen need not make driving different, but do we want it to.
Driving with highest possible “lift-off-regen“: many drivers’ favourite.
The highest setting of “regen” can allow almost one-pedal driving. Using the highest possible regen, with or without one pedal driving, is many drivers’ favourite way of driving an EV either because:
- They are driving a Tesla and low-regen can be less efficient.
- Even though driving a brake-by-wire vehicle, the driver mistakenly believes high-regen is more efficient.
- Regardless of what mode of driving is most efficient, high “lift-off-regen” is regen you can feel, which is more engaging and provides a new and different experience.
Whatever the reason, many are disappointed with vehicles from brands such as Porsche and BYD that provide no option for delivering full regen power via “lift-off-regen” and only provide the highest regen through the brake-by-wire of the “brake-pedal”. Some drivers even mistakenly believing such vehicles have “weak regen”, when the reality is all EVs have strong regen, even if on some EVs it requires using the brake pedal. Lift-off-regen is the regen a driver can feel.
Some EVs only offer their highest regen though a setting for “one-pedal-driving”, but the clearest system is one such in Tesla vehicles, where the regen setting and “stopping mode”, which control the use of friction brakes to supplement regen braking at very low speeds, is a separate control. Contrary to popular myth, regenerative braking is ineffective for bringing vehicles to a complete stop. A high “lift-off-regen” driving mode that still rolls at very low speed allows drivers to train muscle memory for using the brake-pedal as would be used in an emergency, which could be particularly desirable for new drivers.
The only thing required to move from highest possible “lift-off-regen” and one pedal driving, is the addition of a system to stop the vehicle at very low speeds. See the section on “one-deal-driving” for full details.
Tesla low-regen setting and efficiency.
The lack of brake-by-wire means the regen from “lifting off” is the only regen, and thus full regen is only available on the highest regen setting.
Using the Tesla “low” regen setting that was initially available but removed in a late 2020 software update but now reinstated in an April/May 2023 update reduces the amount of regen available to the driver.
The reasons for having a lower “power-pedal” regen setting in a vehicle without brake-by-wire are:
- To provide a more familiar experience for drivers unfamiliar with driving with high regen braking.
- Providing a mode with reduced risk of excess use of regen braking, for use on freeways or other times when little braking may be required.
Without brake-by-wire, the low regen via the power-pedal setting can result in reduced efficiency, and increased reliance on the friction brakes which will increase wear. The low regen setting is best used when vehicles will be driven by drivers unfamiliar with high regen, with Tesla owners best served by becoming familiar with “normal” (full) regen as soon as practical.
Brake-pedal based regen control: An efficient solution for any vehicle with “brake-by-wire”.
An a very efficient alternative to driving with a high “power-pedal” regen setting for drivers of vehicles that are equipped with brake-by-wire is to rely on the computer control regenerative braking when pressing the “brake-pedal” to result in maximum efficiency.
The regen control many reviewers and drivers mistake for “almost no regen”.
Having a much lower regen level for “lift-off-regen” means that when “lifting-off” there is very little braking effect, leaving many drivers feeling very little regenerative braking is in use.
Porsche raised eyebrows when its first EV, the Taycan, debuted without offering a one-pedal driving mode of any sort. It seemed Porsche was leaving an obvious efficiency on the table, though really, it just chose to regenerate energy primarily with the brake pedal. Up to 0.3gs of deceleration—which covers the vast majority of braking events in everyday driving–is handled by motor regeneration, after which point, the friction brakes are added into the mix. Porsche proudly touts that it can put up to 265kW of energy back into the battery pack, which is more than any other automaker. Additionally, the Taycan will even continue to regen when ABS is activated.Road and Track: One-Pedal Driving Isn’t Necessarily the Most Efficient Way of Driving an EV
After years of EV market dominance by Tesla, and ICE vehicles without brake by wire, many people assume that pressing the brake pedal simply activates the friction brakes. For those not being aware of “brake-by-wire” assume Porsche must be crazy to omit high “power-pedal” regen and one-pedal-driving. However, the reality is Porsche offers even higher regen than any Tesla does, just the Porsche only offers that high regen via the brake pedal.
This mindset shaped by experience with Teslas created the false belief that high power-pedal regen is necessary for EV efficiency.
Although technically this approach can offer even greater efficiency that used by Tesla, in practice any gains are difficult to detect, and the main benefit is that drivers do not have to learn a new way of driving. Which would be a big plus if not for the reality that many drivers want to adopt a new way of driving when moving to an EV!
Of the major brands, it is not just Porsche. BYD, the brand producing even more electric vehicles than Tesla, and who even supply battery technology to Tesla, also eschews using the “power-pedal” as the main control of high levels of regen and discourages one-pedal-driving.
With this approach, driving an EV feels like driving an ICEV vehicle. Which, even if technically more efficient, for many drivers is a problem.
Because the main management of regenerative braking results from the driver pressing the “brake-pedal”, lift off regen can be configured as needed to create a familiar driving experience. Because brake-by-wire means that a computer is now controlling what happens when the brake-pedal is pressed, the outcome still feels just the same is the outcome from pressing a conventional brake pedal.
Both power and brake pedals produces responses that feel like what happens with driving an ICE vehicle, even though underneath fully optimised regen is being used whenever braking is required.
The efficiency results from the computer using maximum regen braking before applying the friction brakes, and the efficiency is computer controlled rather than manually controlled.
The biggest negative is that it feels just like driving an ICE vehicle instead of providing the driver a new and different EV driving experience.
Drivers don’t get to feel that regen is at work when braking is activated by the brake-pedal the way they do when it is activated by the power-pedal, but most EVs provide a display indicating the power being either used or regenerated and reading that display can be the only real indication of the role of regen in proving any braking force.
One Pedal Driving: Popular way to drive an EV, or a fad?
What is one pedal driving?
In theory, one-pedal-driving means only one of the two pedal controls in an EV are required during normal driving: the power pedal.
EVs still all have 2 pedals, just as with ICE vehicles with an automatic transmission, because one-pedal-driving does not normal provide emergency stopping power, so the second pedal, the brake pedal, is sometimes required even with the slightly misnamed “one-pedal-driving”. Only “one-pedal-almost-all-of-the-time” gets a bit long.
There is never a third “clutch” pedal control in any current EV, but the “power pedal” and “brake pedal” are both still present with the left pedal as the “Brake pedal” and the right pedal “gas/power pedal” as usual.
Again, that left pedal, the “brake pedal”, is in fact very much still required, it is just in theory rarely required, so the label “one-pedal-driving” is something that can be done for periods of time, but unless the vehicle is trusted to complete all emergency stopping autonomously, one pedal alone is still not enough to always being able to fully control the vehicle.
How one pedal driving works: The steps required.
The is a common misconception that one-pedal-driving make no use of friction braking. This is a misunderstanding.
One pedal braking works by allowing that one pedal to control providing both regen braking and friction braking as needed, and can activate all of the following steps simply as a result of lifting-off the “Power-pedal”:
- Regen braking: Up to the very maximum use of regen braking practical for the vehicle.
- Low speed friction braking: Application of friction brakes to take over from regen braking at very low speeds when regen braking becomes ineffective and only minimum friction braking is require in order to bring a vehicle to a halt and then keep it stationary.
- Supplemental friction braking(optional): An optional but desirable application of the friction brakes to supplement regen braking to provide consistent response in circumstances when the battery is unable to support normal usual levels of regen braking.
Despite the two cases where friction braking is required, unless the brake pedal is used, the regen braking supplies almost all the braking force and the contribution of the friction brakes has a negligible impact on efficiency and little contribution to wear on the friction brakes. However, understanding the role of the friction brakes is key to understanding the limitations of regen braking.
Step 1, regen braking, is well understood, and the limit is the ability of the battery to store the energy from braking. Steps 2 and 3 are less well understood.
Tesla introduced “step 2: low speed friction braking” in 2019 which is what made one-pedal-driving practical in a Tesla:
Stopping Mode enables the 100% one-pedal driving many people have heard about but Tesla has never offered. Tesla cars have almost allowed one-pedal driving, but only slowed to about 3 miles per hour, so you would need to tap on the brakes to avoid rolling into either the intersection or the car ahead of you.Tesla One-Pedal Driving Update — In A Word, Perfecter
The key point being is that without assistance from the friction brakes, there is no “one-pedal-driving”.
Tesla introduced step 3, the automatic use of friction braking to supplement regen braking, perhaps as recently as May 2022 although I had thought Tesla had earlier implementations.
Outside of China, since 2017 the most popular EVs have usually all supported one-pedal-driving since 2017.
The Nissan Leaf introduced one-pedal-driving in 2017, and at that time was the most popular fully electric car in the world and around the time the Tesla Model 3 took over as the biggest selling EV, the Tesla Model 3 also added featured one-pedal-driving.
This means most EV drivers have had access to one-pedal-driving, and many now view one-pedal-driving as a defining feature of a vehicle being a true EV. The misunderstanding is that many people mistakenly think one-pedal-driving is essential for efficient driving of an EV, when there are other alternatives that are, equally efficient, or potentially more efficient.
Whilst some articles do report one pedal driving is NOT the most efficient approach, it is only in vehicles, that unlike Tesla vehicles, are equipped with brake-by-wire that these potentially more efficient approaches as possible. This quite thorough article examines some of the alternatives offered by other brands.
How to configure and optimise one-pedal-driving.
How to configure the EV for one pedal driving varies from EV to EV. For most EVs, it is “regen setting” choice, but for a Tesla, the main requirement is to set the stopping mode to “hold”, and the preferably the “regenerative braking” set to “standard” and not “low” in order to allow maximum possible “Power pedal” regen control.
With one-pedal-driving enabled, an EV will decelerate towards a stop whenever driver stops pressing the “Power pedal”.
In one pedal driving, press the Power pedal harder to go faster and ease off to go slower. Completely easing off the “Power pedal” will make the vehicle stop quickly enough for most situations, which means that the brake pedal will be rarely required.
The two main goals for efficiently using one-pedal-driving, in order are:
- Try to avoid needing the unnecessary of friction brakes.
- Avoiding the unnecessary use of even the regen brakes.
Number 1 is all about avoiding creating situations when more braking force is required than what is available from backing off on the “Power pedal” alone. This requires anticipating traffic and starting braking early.
Number 2 is avoiding the trap of thinking that regen braking is “free” in that it loses no energy at all or even means gaining energy. All energy gained by regen will never be as much as required to get the speed (or altitude) back again.
Given the brake-pedal is still required for an emergency stop, it may be useful to have new drivers spend considerable time without using one-pedal-driving until the reflex for an emergency stop is well established.
Why don’t all EVs feature “One Pedal Driving”?
It becomes a interesting question when you consider there is zero real cost, and the answer is: because they don’t want to!
Even Tesla was “late to the party” with one-pedal-driving, adding the feature as a no cost software update in 2019.
All that is required to provide “one pedal driving” is for the “power-pedal” to be “power-by-wire”, and as all EVs have “power-by-wire” every EV can offer one-pedal-driving by simply providing right software.
All modern EVs have “GO” being “by wire” as the computer controls for the motor. This means that instead of the “power-pedal” mechanically operating mechanical systems to control speed, as was the case with the throttle on the original ICE vehicles, instead with EVs the “power-pedal” provides a signal to the vehicle computer systems.
With this “power-pedal” being “by wire”, the vehicle computer system can determine how to interpret the implications of how far the pedal is pressed. Since the computer has full control over motor power, motor based regenerative braking and, at least on any vehicle with an adaptive cruise control with stop-start, the ability to apply friction braking.
So, any EV can have “One pedal driving”, and all that is required is software.
Reasons a brand does not provide one pedal driving could include:
- Concerns one-pedal-driving can be less efficient than alternatives for brake-by-wire vehicles.
- Concerns over safety as drivers become less practiced as use of the brake pedal.
Any EV that does not have one pedal driving could get one pedal driving through a software update, but it could take a change in philosophy.
Why, or why not, use one-pedal driving?
The logic behind each of the identified for choosing maximum “GO-pedal” regen, suggests in every case it makes sense to add that second step 2 of low-speed friction braking and use one-pedal-driving. Although it is generally a myth that adding this step is more efficient, there is also no reason it would be less efficient. An even more satisfying experience of what feels like engine braking beyond that offered by an ICE vehicle, with zero loss of efficiency.
The overall effect is a new and different driving experience, and most people enjoy new experiences. Many people feel that moving to and EV is far more satisfying if there is also a new driving experience.
Downsides? It can take a little practice, it may not be the most efficient way of driving, and it is important to maintain the reflex to still use the brake pedal in an emergency.
On the subject of practice:
If you’ve ever driven a Tesla, the first time probably went something like this: Everything’s going fine until you need to gently slow down. You lift off the accelerator pedal, and wham! You nearly come to a complete stop. If you have passengers, they probably hate you.Road and Track: One-Pedal Driving Isn’t Necessarily the Most Efficient Way of Driving an EV
This learning curve already applies to use of high-regen, and adding one pedal-driving does not result in there being more to learn, with some even feeling one-pedal-driving make regen more natural, as the strong braking effect continues rather than fading away as the available energy for regenerative braking to harvest falls away.
The biggest potential downside would be if needing to use the brake pedal became too rare, causing the reflex to reach for the brake in an emergency to become “rusty”. There have been some EV crashes where this may have been the cause, but people to failing to brake in an emergency also happens in vehicles without one-pedal-driving.
Is one pedal driving a FAD?
For many, one-pedal-driving has been part of the “EV experience”, but once EVs are common, will it still make sense?
It would make even more sense if we could genuinely eliminate the need to press the brake-pedal, but would we really want to remove any way of overriding “GO” in an autonomous vehicle?
Formula 1 race cars have not adopted one-pedal-driving, which also highlights the limits of the system. One-pedal-driving, by providing no access to full braking force, is inherently limited. It may even be that the use is limited to the vey situations where the goal is “self-driving” as opposed to the racetrack.
Plus, it is not necessarily efficient.
But if it is a fad, then it is clear there is an appetite for something new. Perhaps one-pedal-driving via the “brake-pedal” could be made even more workable, particularly if combined with a degree of self-driving, where the driver can still overrule the system by slowing? It seems to make little sense for the driver to be intervening to go faster, just as it seems illogical to have what is a separate control for “STOP…NOW!”.
Fun vs Efficiency: is one-pedal-driving or high regen more efficient or more fun?
What are the options?
It very much depends on whether you are happy with an EV that drives like an ICE vehicle. A Tesla is very much designed for people who want something different, while owners of an EV Porsche may want an EV that still drives like a Porsche. If the vehicle will be predominantly vehicle will be using adaptive cruise control or autonomous driving, then settings for how the pedals behave should have negligible impact on efficiency, so the priority may be what a question of the driver finds more fun when they do take over.
There are a few scenarios that depend on vehicle:
- For a Tesla the choice will normally one-pedal-driving but perhaps a choice of low-regen for maximum range on a long bland freeway, although in those circumstances the vehicle maybe self-driving anyway.
- For a Porsche or BYD* and some others its low regen for efficiency or performance but while there somewhat higher lift-off-regen for a possible change, there is no option of no one-pedal-driving and regen is mainly regen via brake-pedal-regen.
- For almost all other EVs, it is choice of being like a Tesla for fun and something different or provided there is brake-by-wire unlike a Tesla, then using low regen like a Porsche or BYD for maximum efficiency.
The beg caveat is that many times when driving for efficiency, autonomous driving may be active, so the settings may more be about whatever the driver prefers, of for when efficiency is not important.
*While all Porsches are performance vehicles and BYD vehicles can include the Seal or U9, but although not all BYD vehicles are known for performance there is still no one-pedal-driving.
Making a choice: For most driving, do what you enjoy, that will work best!
In a Tesla, or any other vehicle without brake-by-wire, a higher regen setting does technically enable more efficient driving.
In any vehicle with brake-by-wire, the same efficiency is technically possible with any available setting, and all regen settings do is change which pedal is activating the regen.
In practice, even though the same efficiency is possible with different settings, achieving the technically possible optimum efficiency does get easier with a lower regen setting. One-pedal-driving is in reality more about driving fun than efficiency, and not matter how many myths people choose to believe, the two have rarely gone hand .
But also in practice, efficiency in an EV matters most because range matters most when on a long trip on a quite bland highway, which is normally when there is far less braking, which will usually mean there is least to gain from regenerative braking and most to lose controls being overly sensitive resulting in applying unneeded braking.
Even when driving in urban conditions, where EVs are all so much more efficient than ICEVs that small differences in efficiency often matter, many drivers are often using adaptive cruise control or other driver aids, which result in the human driver rarely pressing the “GO-pedal” anyway.
A practical example.
With a Tesla, if you cannot get better result with “standard” regen, then you may need more practice. I conducted some tests with a BYD vehicle with brake-by-wire, and personally found I consistently achieved slightly better efficiency using a the lowest “regen” setting. Working harder to avoid “lifting-off” more than absolutely necessary and thus avoid activating regenerative braking more than necessary, and it was sometimes more work, but did marginally improve results which confirms that changing regen settings can make efficient driving less work.
But a big surprise when I found a learner-driver I had been instructing achieved better efficiency than I did over a similar course. I have been trained in rally, racing and advanced driving, and yet a learner who still had more to learn could be more efficient? Really? Further analysis revealed they were driving slightly slower on average, and this was the reason. In reality, if you want a little more efficiency, driving slower is a simpler and more effective manner than almost anything else, but it is less fun.
For maximum highway range: use the lowest “regen” if possible.
There can be times when maximum range is needed to reach the next possible charging point, and on the few occasions this does occur, it will be when travelling between towns or cities on the highway.
With a Tesla or a vehicle or without brake-by-wire, “if possible” means “if driving on low-regen does not result in needing use of the brake pedal under normal conditions”. If low regen is possible, it will make fine control of the amount of regen simpler. However, if the vehicles will be using adaptive cruise or autonomous driving the entire time, the setting may make no difference.
With any EV with brake-by-wire, which so far means any EV other than a Tesla, low-regen should, and normally will, be the safest way to ensure maximum range. Also consider the more technical answer.
The more technical answer.
There is evidence that Porsche is correct, and that in vehicles equipped with brake-by-wire, a very low “regen” setting will be most efficient, even though for those accustomed to Tesla vehicles, this can feel like “there is no regen!”
Tesla makes a high regen standard for a reason, but then added the option restored the low regen option for a reason.
Follow brand guidelines. If brand has a recommend setting, there is a reason. Also, it is worth considering if the guideline for when to use a setting apply for the situation in question. Many guidelines are designed around the testing procedures for consumption the car will need to pass such as EPA, WLTP, etc. as having the best figures on these tests can really help sales.
Brands work very hard at achieving the best efficiency for the vehicles during the test cycles.
Unintended acceleration and one pedal driving.
Wikipedia currently 6 factors as potentially responsible for sudden unintended acceleration:
- Pedal misapplication
- Unresponsive (entrapped) pedals
- Electronic throttle control or cruise control failure (see drive by wire)
- Stuck throttle (unrelated to pedal position)
- Shorting of tin whiskers
- Diesel engine runaway – excessive pressure in the crankcase can force mist of engine oil into the intake manifold, which can be burned in the same fashion as diesel fuel.
The only link being suggested here between one pedal driving and unintended acceleration is “Pedal misapplication”. This is the type of unintended acceleration that can be considered as the fault of the driver, because it is the driver pressing the accelerator instead of the brake when they wish to stop the car. Many learner drivers make this mistake at least once while learning, but over time pressing the brake pedal to stop becomes “muscle memory” that no longer requires conscious thought. But could use of one-pedal-driving result in new drivers have a weaker muscle memory to push the brake pedal, potentially resulting in increased unintended acceleration as a result of pedal misapplication?
The answer so far is “maybe”? Being a theorist, not an experimentalist, I look for data collected by others and will link data here:
- Whistleblower Drops 100 Gigabytes of Tesla Secrets to German News Site: Report
- Tesla recalls over 1.1 million vehicles in China for issues including regenerative braking strategy
- Fatal accident puts Tesla in spotlight in China
Background: An In depth look at brakes of varied types.
The principle of braking: Conversation of energy.
There is a principle of physics: Energy is never created or destroyed.
Energy from the battery or fuel tank is converted into kinetic energy: the energy of motion.
The goal of brakes is to reduce speed, which requires converting the energy of motion into a different form of energy. The rule “energy is never created or destroyed” means braking will always be transforming kinetic energy into another form of energy.
Every type of brake needs to have a way to dissipate the energy produced by concerting the kinetic energy into a new form of energy.
Friction brakes transform the kinetic energy into heat and must be able to dispose of the heat in order to continue converting kinetic energy into heat.
Disc brakes and drum brakes are both types of friction brakes. Friction brakes convert the kinetic energy into heat energy. The hotter friction brakes become, the less effective they become as their capacity to accept even more heat becomes reduced. To not lose effectiveness, friction brakes need to be able to dissipate heat, which gives rise to ventilated disc brakes.
Internal combustion engine braking.
The engine braking of a combustion engine also converts kinetic energy into heat, by using motion to pump or suck and compress the air in the cylinders. Compressing the air raises the temperature of the air, which is pumped through the engine transferring heat to the cylinder block and out through the exhaust.
Just for completeness, “air brakes” are not a form of air compression braking, but simply and alternative way of operating friction brakes.
Regen brakes transform the kinetic energy of motion into electrical energy, in much the same way as friction brakes transform the kinetic energy into heat. Just as friction brakes need to be able to dissipate heat to remain able to convert motion into heat, regen brakes must dispose of electrical energy by storing that energy in order to continue converting kinetic energy into electrical energy.
Note that regen braking is just one form of possible braking by than electric motor: it is the efficient braking that recovers energy, but it is not effective at very low speeds or as a parking brake.
There is an alternative way of braking using an electric motor that can be effective even at low speeds by being battery powered in order to exert a force against the current motion of the motor, but this uses energy rather than generates energy. It can work but is not “regen”. An electric motor can also be used as a parking brake by being powered to exert force to resist a stationary motor beginning to spin or rotate, but again this consumes energy, and is not an efficient use of electric charge, and thus is not “regen”.
Both of these uses of the motor would consume energy from the battery as well as generate heat and would be even less efficient even than friction braking, which wastes energy, but does not consume energy! For this reason, neither of these not regenerative braking approaches is used, and friction brakes are used to provide parking brake functionality, and at very low speeds and any time additional braking beyond what regen braking can provide is required.
Regenerative brakes use an electric motor, with the motor configured to operating as a generator, and thus to convert kinetic energy into electrical energy.
How this works, is that moving a magnet past a conducting coil generates a voltage. The means that, since rotating an electric motor rotates a coil past magnets, rotating a permanent magnet electric or induction motor with power to the magnets will generate voltage. Since generating voltage requires energy, this creates resistance to rotation, but once the motor is up to speed, as maintaining the voltage requires no extra energy, the resistance diminishes.
However, if an electrical load such as a circuit with a battery is connected across the coil causing a drop in voltage, spinning the motor will then require whatever force is necessary to restore the voltage. Add the electrical load which consumes some of the voltage, and the motor becomes hard to turn. This is regenerative braking.
Observing the principles by testing.
These principles can all be tested with an appropriate electric scooter or electric bike. I have tested with a Unagi scooter which seems to use induction motors, so it needs to be switched on to see the effects and there is no noticeable resistance to pushing the scooter when it is “off”. This is as would be expected from induction motors and is consistent with the scooter being able to offer selection between either single or dual motor operation. When “on”, there is force needed to start the scooter rolling, but once at walking speed there is negligible resistance to keeping the scooter rolling. The Unagi scooter has regen braking that cannot fully stop the scooter but can slow the scooter sufficiently for the rider to need to use one foot for stability.
The power of regen braking is determined by the amount of power produced by the electrical “load” of the circuit charging the battery. At very low speeds, there is insufficient voltage to power the circuitry that charges the battery,
The effectiveness of the regenerative braking is reliant on the ability to ‘dissipate’ electrical energy by storing that energy it in the battery. Without keeping the voltage at the motor below the voltage generated by spinning coils in a magnetic field, the braking effect would become minimal far sooner than a friction brake becomes too hot, but as long as the electric power can be transferred to the battery as electrical charge, regenerative brakes can prove an effective and almost wear free brake system that generates electricity. The latest Formula-E race cars, have no other rear brakes!
What really limits regenerative braking?
In a vehicle without brake-by-wire, regen available at any given time could be limited by the amount available from lifting off the accelerator, but that is more a question of how much regen braking will be applied in specific control modes, rather than the capability of the vehicle to apply regen braking.
The amount of regen braking a vehicle can possibly apply is mostly determined by:
- The power of the motor(s).
- Front-wheel-drive vs rear-wheel-drive vs all-wheel-drive.
- The ability of the battery to accept charge.
The power of the motor(s): the more powerful a motor, the more deceleration it can provide, and hopefully this needs no further explaining.
The ability of the battery to accept charge: This is usually the main limiting factor. Braking requires converting the energy of movement, kinetic energy, into another form of energy: heat in the case of friction brakes and electrical energy in the case or regenerative brakes. Just as friction braking is limited by the amount of heat that brake discs or drums can dissipate; regen brakes are limited by the amount of electric charge they can dissipate via storing the charge in the battery. A vehicle with a flat charging curve can handle a similar amount of max regen at all levels of charge, while a vehicle with a peaky charge curve will likely vary more in terms of regen braking capability relative to state of charge. Many vehicles have regen-charging limits higher than the regular charging limits, which due to the much shorter duration of high regen during the most intense braking will not result in any problems for battery life.
Front-wheel-drive vs rear-wheel-drive vs all-wheel-drive: While wheels most limiting traction for handling around curves and for acceleration are the rear wheels, the grip available to the front wheels is most critical for stopping as most weight shifts forward to the front wheels during deceleration. The best possible result for regen braking is from most regen braking power from the front motor and less regen braking power from rear motor. Ultimate regen braking power, as with Formula-E is determined mostly by the regen braking of the front motor, but the gentler the braking, the less critical it becomes whether the braking is from the front or rear, but the best balance will aways be when the front wheels are doing most of the braking.
The result is the friction brakes are needed most in a rear-wheel-drive vehicles, less in front-wheel drive-vehicle, and even less in all-wheel-drive vehicles. Rear wheel drive better for ‘go’, front wheel drive better for ‘stop’.
Other new horizons for vehicle control.
Steering by wire and funny yokes.
Several brands see the introduction of new EVs as an opportunity to introduce new controls. Telsa, Lexus and BYD among those looking at steering yokes, that look similar to those in F1. Note that in F1, the steering yoke can only be rotated by slightly less than a half circle in either direction, which allows the drive to keep their hands in place with no need for arms to cross. An F1 car has a huge turning circle and would be useless in a car park. Even on the racing track, it is necessary to spin the rear wheels and force a slide to do a U-turn. Getting a yoke to work in a vehicle that must also be maneuverable in a parking lot is a very different challenge.
This video gives some analysis, but it deserves more, and I do not think Lexus is there yet either.
Camera based “mirrors”.
This is another new topic, with analysis still to be added.
The challenge of replacing mirrors with cameras is that while driver can manoeuvre their head to “pan” the view available in a mirror, no one has yet provided an equivalent for that ability of the driver to change the view with a camera-based system.
- 2023 Nov 7 th: Updated terminology for clarity and new “Regen: Two Systems” section.
- 2023 May 27 th: Added “Unintended acceleration and one pedal driving“.
- 2023 May 12 th: launch as a stand-alone page.
- 2023 January 7 : More on one pedal driving.
Future Updates: Induction and other content to follow….