Naked Science Forum
Non Life Sciences => Technology => Topic started by: paul cotter on 23/04/2024 17:36:38
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Driving the boss' car(hybrid), as my own has expired, I have noticed some concerning behaviour.(1) When I lift my foot off the throttle pedal the car slows down more rapidly than a non hybrid due to regenerative braking. (2) Moving the selector from D to B one can achieve much greater retardation through an enhanced regenerative process. All well and good as regards fuel economy but neither function appears to activate the rear brake lights such that a driver following would be missing the required visual cue. Unless the lights are activated at a certain speed- I was driving along our ~30m driveway watching for reflection off a window and my speed was obviously quite limited.
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When I lift my foot off the throttle pedal the car slows down more rapidly than a non hybrid due to regenerative braking.
Interesting design choice. Any car slows when you lift off the throttle due to engine braking (unless you disengage), but this choice seems to suggest that the pedal is interpreted as an absolute speed suggestion and not a throttle (power suggestion). This interpretation lets you maintain more constant speed over small hills without so much reaction required at the pedal.
Moving the selector from D to B one can achieve much greater retardation through an enhanced regenerative process.
What is B? (for those who've never seen a B as a valid selection). We with non-hybrids have the low gears, useful for engine braking down hills. Maybe B is a non-American thing.
All well and good as regards fuel economy but neither function appears to activate the rear brake lights such that a driver following would be missing the required visual cue.
Engine braking similarly does not activate the lights. I've used the effect to attempt to ward off tailgaters. I've also been targetted by an insurance fraud guy that attempts to quickly stop without change to the lights (done by riding brakes). It didn't work. Yay reflexes.
Anyway, lack of brake lights during light braking is not new, so can't say it's a new danger with the hybrids.
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Hi Halc. When I take my foot off the "pedal", call it what you want, regenerative braking starts immediately. This is an automatic with park, reverse, neutral, drive and "B", there is no 1 and 2 as on a regular automatic. The B position is for more extreme regenerative braking. If I dropped down through the gears in a manual the retardation could easily be similar but this is not quite comparable as I see it as it depends on one's driving habits. In Ireland when changing down in a manual the recommended method is to lightly touch the brakes as one disengages the clutch and then to take one's foot off the brake when the lower gear has been accessed and then to repeat as necessary. Not saying I do this but if done, the following driver sees the momentary brake applications. Rules may be different in the states.
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the pedal is interpreted as an absolute speed suggestion and not a throttle (power suggestion). This interpretation lets you maintain more constant speed over small hills without so much reaction required at the pedal.
Cruise controls maintain a constant speed as the gradient changes, unlike drivers' right feet, which leaves the strange feeling that you're accelerating uphill and decelerating downhill. Other drivers around you also make the same mistake.
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Hi.
In Ireland when changing down in a manual the recommended method is to lightly touch the brakes
As far as I know that's not written in the "highway code" booklet (for the mainland UK) or generally expected - but I have once had such advice from my driving instructor.
There are also alternatives, like double de-clutching (double clutching in the U.S.): The strongest slowing down effect is caused within moments of lifting your foot off the clutch pedal when you change to a lower gear. This is when the engine, drive shafts on the engine side of the gear box and gear wheels in the gear box which were only spinning at (for example) 2000 rpm has to increase to 3000 rpm since you are initially at the same road speed but will now be in a lower gear. An option then is to shift gear to neutral, ensure the clutch pedal is then released, briefly touch the accelerator pedal to spin everything (engine and the gears in the gear box) and then clutch and shift again to the new lower gear. This isn't in the highway code either but it can be done and you will soon get quite good at it.
https://en.wikipedia.org/wiki/Double_clutching_(technique) (that article talks about reducing wear-and-tear rather than application in racing).
Another level up again is to just change gear without even using the clutch pedal. You ease your foot slightly on the accelerator to reduce the pressure or contact force between gear teeth, then move the gear stick to neutral, then increase pressure on the accelator again (but it won't be any seconds, just milli-seconds because without any load the engine will pick up rpm almost instantly), then when the new gear is spinning at about the right rpm you'll push the gear stick again and engage the new gear while everything is still spinning. With a lot of practice (which involves a lot of terrible noises from the gearbox while you fail) you can perfect this. To practise this, the usual requirement is to use your dads car and be about 17 - 18 years old. Your dad will have enough money to get their gearbox repaired and re-built after all the times you failed and have broken gear wheel teeth while trying to enage a gear wheel spinning for 4000 rpm to another gear wheel that was only spinning for 2000 rpm etc. (and after-all, new drivers do make mistakes even while making less extreme racing gear changes). Once you own your own car, you won't try it again because the technique of double de-clutching is actually good enough and considerably cheaper.
Anyway, all of these driving techniques are fast becoming obselete because most new cars will be fully automatic. These days, they (automatics) are better and don't result in a loss of performance (e.g. fuel economy).
I suppose we should address the original question:
Does regenerative braking have a hazardous complication?
Possibly but the driver behind shouldn't be following that close. If they are then according to the highway code you must now adjust your own driving appropriately. For example, reduce your speed so that they can stop in their braking distance. It's not exactly what they deserve but it's what is safe and recommended. Her Majesty's Secret Service takes a dim view of it if we keep deploying the special counter measures on ordinary civillian drivers who were just too close.
Best Wishes.
[ These days Her = His but all the films are based on Her Majesty's Secret Service ]
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[ These days Her = His
Very woke. Or possibly medieval, depending on how you look at it.
And speaking of the middle ages, should mine horse decide on a whim to stop suddenly without illuminating its posterior lantern, wouldst not the following rider be liable should he collide with us?
Not entirely irrelevant. The father of a childhood friend was unable to claim insurance for a hoofprint in the bonnet (hood) of his Daimler Dart (O blessed memory) because the Usurers of Lloyds Coffee House said he must have been driving too close to said animal.
Yea, bang up to date, forsooth, you may have seen recent TV footage of a couple of riderless horses cantering through London and colliding with various horseless carriages. The official explanation that they were military horses (as indeed they were) spooked by a loud noise (ibid) makes one wonder: hath not the British Army adopted ye musket, nay even the drum and bugle? Or were they perhaps Special Forces steeds trained with rubber shoes and covert whinnies?
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but neither function appears to activate the rear brake lights...
My car (fully EV, Polestar 2) can be set to one pedal or two pedal driving; the former makes maximum use of regenerative breaking and I barely need to use the brakes. It definitely puts the brake lights on in this mode.
So maybe this is a foible of some makes?
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Thanks Chris, that is an interesting observation. The car I am referring to may operate the brake lights during retardation at a higher speed than that which I was limited to in a ~30m driveway. Any strong retardation should activate the rear brake lights, in my opinion. Anything that adds to even a marginal increase in safety at no or negligible cost is a no-brainer.
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I completely agree. Definitely safer if the car behind knows you are slowing down.
That said, in my previous car, and in my wife's present (non EV) car, just taking your foot off the accelerator (and hence slowing down) does not trigger a brake light warning, although the rate of deceleration is obviously considerably slower.
Maybe it's a rate thing? Is there a standard set by the industry to address this? ie slow down at more than a specific rate and that's regarded as "braking" and needs a warning light?
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Definitely safer if the car behind knows you are slowing down.
Did anyone ever check whether the introduction of brake lights resulted in people following closer behind the car in front?
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That indeed is a possible unintended consequence- whether it has been researched, I do not know.
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Most lights these days are appaling, the indicators have been shrunk so you cannot see them, brakelights are numerous and blinding so when in stationary traffic you are blinded by the car infront, and headlights have become dazzling.
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Did anyone ever check whether the introduction of brake lights resulted in people following closer behind the car in front?
As they have been mandatory for about 100 years it would be difficult to disentangle this hypothesis from the statistics of increased traffic density, increased speeds, mandatory speed limits, improved tyre treads, and brakes that actually work.
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Maybe it's a rate thing? Is there a standard set by the industry to address this? ie slow down at more than a specific rate and that's regarded as "braking" and needs a warning light?
A rate thing but also a suddenness thing. If I am gently engine-braking down a hill, it would be unsafe to have the brake lights on all the way. What if a deer suddenly pops in front? Now I hit the brake hard and the guy behind me takes considerably longer to react because my brake lights haven't changed state.
This effect BTW is the MO of insurance fraud traps, at least one of which I've been a target. Heavy dense traffic, but at speed, and the car ahead of me has brake lights on for some time without slowing. Suddenly when I'm close he hits it hard, hoping to cash in on my insurance. Didn't work. If I'm that close in heavy traffic, my foot is already hovering on the brake pedal, something I cannot do if the car is going to brake every time I take my foot off the accelerator.
My car (fully EV, Polestar 2) can be set to one pedal or two pedal driving; the former makes maximum use of regenerative breaking and I barely need to use the brakes.
How does that work? Take your foot off and the car does full panic braking? Anything less and you either need to use that other pedal in 1-pedal mode, or you have to be really precise at all times as to the pedal pressure being applied.
How does cruise control work with 1-pedal systems?
If the brake lights are to come on at any level of regenerative braking, does cruise control need to put on the brake lights every time it goes down hill despite not slowing down?
Another note: How efficient is regenerative braking. How much energy is lost regenerating and then re-accelerating? How can an EV get decent range if it cannot just coast and allow a minor variation in speed?
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Hi Halc, I think what Chris is referring to as "one pedal" driving is operating with the selector in the "B" position that I alluded to. In that scenario the "throttle" pedal gives normal torque to the wheels when depressed such that it appears identical to operating with D selected. When the pedal is released a quite severe retardation is applied, much more than in the D position. As such unless hard braking is required there is no need to use the brake pedal but it is available if needed. I have only used the boss' car a little as I try to reinstate my own vehicle so what I have said may not be accurate. Also previously I have only driven manual petrol(gasoline) models and this is my first experience with a hybrid.
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That indeed is a possible unintended consequence- whether it has been researched, I do not know.
I think I do.
As they have been mandatory for about 100 years it would be difficult to disentangle this hypothesis from the statistics of increased traffic density, increased speeds, mandatory speed limits, improved tyre treads, and brakes that actually work.
That's why I asked.
I recently spoke to a guy on Twitter who designed side-impact protection for cars, so I asked him if there was any evidence that SIP had saved any lives. He didn't have an answer, and the more I pressed him the more he squirmed.
People just assume that if something's intended to save lives, then it does save lives. Drugs would probably be an exception, generally they don't get a a licence without some evidence that they work first.
My car (fully EV, Polestar 2) can be set to one pedal or two pedal driving; the former makes maximum use of regenerative breaking and I barely need to use the brakes. It definitely puts the brake lights on in this mode.
I've never driven an electric car, but I don't like the idea of having braking shared between two pedals rather than separate pedals for brake and accelerator. I can foresee dangerous dithering: if an emergency starts to develop I can imagine being undecided whether staying on one pedal will provide enough brake force or whether I need to move to the other. That's not going to be conducive to fast reaction time, and if you continue jumping for the brake automatically like in an ICE car it risks creating a pile up with unnecessarily sharp braking. Far better to put your foot on the brake, and then just modulate the pressure according to how the situation develops.
I think I'd want a switch for a "simulate ICE" mode, in which the regenerative braking simulates engine overrun unless I swap to the brake pedal.
Another note: How efficient is regenerative braking. How much energy is lost regenerating and then re-accelerating? How can an EV get decent range if it cannot just coast and allow a minor variation in speed?
I suppose the answer would have to be that you can still coast by adjusting your foot position accurately/carefully enough, but I doubt people will, and the idea doesn't appeal to me much.
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I recently spoke to a guy on Twitter who designed side-impact protection for cars, so I asked him if there was any evidence that SIP had saved any lives. He didn't have an answer, and the more I pressed him the more he squirmed.
It's relatively easy to assess the damage to occupants caused by a lateral collision, then check the statistics of percentage fatalities normalised by probable impact speed. Intuitively, I doubt that anyone is more tempted to drive into vehicle A rather than B because A has SIP, so a first-order approximation would suffice.
Drug licencing depends on where you are. In the USA it has to be "no worse than" or "significantly cheaper than" an existing product and in the EU it doesn't actually have to work at all, as long as it meets production quality control standards.