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No more brakes for cars of the future:
Electric cars of the future could be able to ditch conventional brake technology in favour of powerful regeneration by battery-powered motors.
[...] Electric cars already use a combination of conventional friction braking and brake regeneration. The latter slows down vehicles using resistance from the same electric motor that propels the car, feeding that energy into the car's battery to extend its range.
DS, Citroen's luxury arm, said it is "exploring whether regenerative braking alone could eventually be the sole method to slow cars down, helping to better recharge the battery in the process, and doing away with conventional brake discs and pads".
[...] [Conventional brake pads and drums] produce "brake dust", fine particles of metallic material that separates from the pad and disc as part of the braking process.
[...] Dr Asma Beji, a non-exhaust particles expert, said in June 2021 that "the impact on health of brake wear particles is undeniable and cannot be neglected".
[...] Environmental researcher Dr Liza Selley, published a paper for the MRC Centre for Environment and Health at King's College London and Imperial College London in 2020 that suggested "diesel fumes and brake dust appear to be as bad as each other in terms of toxicity in macrophages".
[...] "Macrophages protect the lung from microbes and infections and regulate inflammation, but we found that when they're exposed to brake dust they can no longer take up bacteria.
"Worryingly, this means that brake dust could be contributing to what I call 'London throat' – the constant froggy feeling and string of coughs and colds that city dwellers endure – and more serious infections like pneumonia or bronchitis which we already know to be influenced by diesel exhaust exposure."
DS and other manufacturers including Jaguar and Porsche participate in Formula E electric car racing. The series will eliminate rear disc brakes from its next-generation machines in a bid to improve real-world research into the performance potential of purely regenerative braking.
(Score: 3, Interesting) by Zinho on Thursday May 12 2022, @12:30AM (12 children)
I was under the impression that shorting the ends of a motor worked best as a brake when it was a dead short: i.e. no resistance across the motor's poles. I thought that was why the physical brakes were there - that the effect of regenerative braking was reduced the lower the car's speed - and so the brake pads took up the slack at low speeds.
Does charging the battery give better braking performance than a dead short? If so, why aren't they used exclusively? Are the car designers wanting a manual backup in case of software bugs?
Inquiring minds want to know.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 0) by Anonymous Coward on Thursday May 12 2022, @12:55AM (4 children)
Well, majored in EE in college anyway.
Motor and generator are the two sides of a same coin. Motor converts electric energy into mechanical energy by rotating the rotor. Generator converts mechanical energy (usually from rotating rotor) into electrical energy.
Have no idea what you mean by "shorting the motor,"
Over to you better EEs and the ones familiar with regenerative brakes.
(Score: 5, Informative) by RS3 on Thursday May 12 2022, @02:00AM (3 children)
In a simplification motor and generator might be the same, but in reality optimizations make a motor much better at being a motor, same for generator.
Some motors, mainly "induction motors", won't behave as a generator to any useful extent. And, in fact, electric car motors are, from what I see and read, "induction motors".
Torque: rotational (turning) force
As most people know, a motor generally involves magnetic attraction. We generally have a stator (part that does not turn) and a rotor- part that turns. Some motors have permanent magnets in the rotor, and "field coils" around the perimeter (my washing machine for example, and most new ones). Generally the coils are arranged and wired in 3 "phases". So you energize one coil, and as the rotor moves and the magnets start to align, you now energize the next coil, de-energizing the first coil, and the rotor moves toward the 2nd coil. And so on for the 3rd coil. (Actually it's more complicated than that; ask if you want to know...)
There's a type of motor called "stepper motor" and they're generally like I described above, but usually with 4 phases. They're used in many positioning systems, like the X-Y-Z drives of 3D printer, driving the print head belt in inkjet printers, and many other positioning systems.
Anyway, there are motors without permanent magnets in the rotor, especially older ones made before the super magnets (neodymium, cobalt, etc. alloys) and they had electromagnets (coils) in the rotor (aka armature). Electrical contacts called brushes rubbed on a rotating contact assembly called a "commutator" to get the electricity into the armature coils. Many many motors are made this way and have been since 1800s. Edison made tons of motors that way. They're easy to reverse, easy to control speed, lots of torque and power, can spin very fast and are often very noisey. Most vacuum cleaners have this type of motor, many power tools. And they can run on AC or DC equally well.
Older car generators usually worked this way. The outer field coils were energized by the battery, and the rotating armature caused electric current to flow in the armature coils, through the commutator and brushes, and powered the car and charged the battery. You easily regulate the output by varying the current in the field coils. The output from the armature is DC. in these.
I have a garden tractor that has a motor/generator- one of these ^. It's not very efficient at either, though.
Another type of motor is the "induction motor". It uses AC in stator (field) coils, and due to various designs (inductive and/or capacitive) a rotating magnetic field is created. (Ask if you want to know more about this...) The rotor needs to be magnetically attracted (force) to create torque, right? Just plain steel won't give much pull, so output torque and power would be very low. Nikola Tesla came up with a clever design where the AC in the field coils "induces" an electric current in copper wires embedded in the rotor. In fact, the more you resist the motor's turning (heavier load), the more the induced rotor current, so the stronger the rotor magnetic field, and the harder the motor works. Very very clever. Induction motors are everywhere. Used to be used in washing machines, dishwashers, dryers, pumps, refrigerator compressors, etc. They come in a huge variety of sizes, up to and above 10,000 HP (horsepower, 0.746 KW.)
So again, electric car motors are generally 3-phase induction motors. To get them to generate electricity, for regenerative braking, you have to do some very clever electronic controls to keep rotor current going, but still extract power from the whole thing.
* Most gasoline engines have an "alternator" to generate electricity. It's pretty simple: rather than the more complicated commutator with many copper segments and many armature coils, they just have 1 armature coil, and 2 simple "slip rings" to get current into the rotating electromagnet that is the armature. The field coils are where you get the generated power, and it's AC. In most cars there are 3 stator phases (popular, huh?) and 6 diodes to "rectify" the 3-phase AC into DC for the car. Again, it's very easy to vary the armature current to regulate the output.
(Score: 3, Insightful) by Beryllium Sphere (r) on Thursday May 12 2022, @02:09AM (2 children)
Both the electric motors in my Prius are motor/generators and regenerative braking is mature technology. The problem is that there's a limit to how fast a battery can absorb power and a contingency stop can far exceed that limit. Another problem is that it's a safety-critical system and it is not necessarily easy to match the reliability of pads scraping on a disk.
(Score: 5, Insightful) by RS3 on Thursday May 12 2022, @02:28AM (1 child)
Actually your Prius has separate motor and generator: induction motor, PM rotor generator: https://www.researchgate.net/figure/Motor-generator-and-engine-of-Toyota-Prius-hybrid-THS-II-System-6_fig4_265995537 [researchgate.net]
I will always endorse regenerative braking, but yes, I 100% agree it would be beyond ludicrous stupid to eliminate friction brakes from any vehicle.
Interesting thing: a good friend has a Chevy Bolt he's had for 3+ years. AFAIK, he's had very little trouble with it, but I'll check with him.
Anyway, it does NOT do regenerative braking by default! I though that was stupid! He can put it in a mode where when he lets off the accelerator it regeneratively brakes, and there are several levels. At the highest level, it jerks you forward (sorry, it "derivative's of acceleration"s you forward! :)
IMHO, regenerative braking should happen with the brake pedal! Like as soon as you move the pedal a little. The harder you press the brake pedal, the more it should "pull" power from car's inertia, then at some point (pedal pressure) it should begin to apply friction brakes if needed.
(Score: 3, Funny) by coolgopher on Thursday May 12 2022, @06:19AM
I appreciate that jounce of word play!
(Score: 5, Informative) by lentilla on Thursday May 12 2022, @01:46AM (4 children)
Torque is proportional to the ampere-turns in a direct current (DC) motor. Or: in simple terms, the greater the current, the greater the acceleration.
Assume you have a motor connected to a set of wheels and you are rolling along at speed on a flat surface:
(Score: 0) by Anonymous Coward on Thursday May 12 2022, @02:00AM (3 children)
i.e, turn the motor into a generator - suck the momentum out.
(Score: 2) by kazzie on Thursday May 12 2022, @05:05AM (1 child)
A downside of reversing the terminals (or "plugging" ) is that all the kinetic energy is dissipated as heat within the motor's windings. It's great for a fast emergency stop, but not for regular usage.
(Score: 2) by maxwell demon on Thursday May 12 2022, @07:53AM
I'd say if you feel the need for it in regular usage, you really should rethink your driving style.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Thursday May 12 2022, @06:04AM
Doesn't the Segway control system do something like this?
If you can develop enough enough torque to "burn rubber" (forward), the physics should work to "burn rubber" (reverse).
What I am getting at is that under normal driving circumstances, regenerative braking should be sufficient most of the time, but if necessary, you have the power to forcibly brake, using energy to do so, but it will stop the vehicle every bit as fast as the most advanced mechanical antilock braking possible. It won't be efficient, but it will stop the car as quickly as possible, like ramming a car into reverse direction, which would likely flat take out a transmission. Kinda hard to take out a magnetic field though.
However, everything breaks, and for something as critical as braking, should the braking circuit fail, I would advise a single use mechanical brake be released to lock up the wheels, kinda like we use an air bag - not to be deployed until electronic braking malfunction detected. Once released, one would have to park the car and manually reset all four wheels. If the electronic braking is still detected to be malfunctioning upon attempted drive off, it will simply trip the mechanical brake again.
This might be useful for anti theft as well. It would force someone to use inordinate amounts of time trying to move the vehicle.
Time for the tow truck.
Of course, once the vehicle is parked, everything is powered down, and a mechanical pawl could be used in each wheel to lock all four wheels very similar to how an automatic transmission is locked up with a pawl in Park mode.
I am thinking minimal mechanical moving parts/bearings by using a hub motor in each wheel, including ability to still move the car even if only one motor still works, but severely speed limited as that single motor will also have to stop the car as well, and a panic stop will engage the emergency brake, that most likely you would have to visit each wheel to reset it. ( Gotta make emergency brake reset a PITA so people won't ignore it and glibly use their last braking system to failure).
I would not want to design something dangerous, neither would I want to design anything that leaves their owner stranded if it could have limped home.
Here's the rub though... Just how many of us would have an innate ability to comprehend the problem and be able to compensate? Stuff like this seems to come naturally to people with engineering interests, but would others comprehend the situation? I ask because about a year ago, one of my friend's wife almost made it home, with the oil light on. Only about 10 more miles and she would have made it.
(Score: 2) by kazzie on Thursday May 12 2022, @05:15AM
The advantange of using an external resistor or battery charger is that the excess energy is dissipated there, rather than in the motor.
The disadvantage of using them is that they limit the current flow, and thus the rate at which energy is dissipated. But if you're dissipating it in the motor, it could end up seeing 3 or 5 times (I forget which) it's rated power sent through its windings. You'd need to seriously overengineer your motor if you were going to short/plug it on a regular basis.
(Score: 2) by Immerman on Thursday May 12 2022, @10:19PM
I believe the maximum deceleration torque possible from a motor is generally achieved by applying maximum power to the motor in reverse.
My motor-physics knowledge has faded greatly, but my gut says that shorting the terminals of a DC permanent magnet motor would provide braking force, since you're inducing current in the windings that will resist the changing magnetic field (akin to the way a magnet dropping through a copper pipe in slow motion. But not nearly as much as actively powering that resistance. (akin to firing a railgun upwards, to overextend )
However, if I recall correctly many (most?) modern car motors are actually computer-controlled multi-phase AC motors that contain no permanent magnets, which can be considerably more efficient (as well as being considerably cheaper since they don't require any expensive rare earths for high-strength permanent magnets.)
The efficiency gains are in part because without permanent magnets there are none of those induced "braking" currents when coasting.