I don't own a hybrid, but have had a question about them on my mind:
We know that on hybrid cars like the Prius, during braking the battery is recharged as the wheels act like generators. But I wonder about two things:
- Is there a conventional braking system pressing metal against metal as a backup for these cars in case the generator function during braking doesn't work properly; and
- If so, what kind of wear does this backup braking system endure, in general (presumably far less than on conventional cars.)
There is a conventional braking system but it is brake pad material against metal, not metal against metal (unless you don't replace the pads after they are worn).
The service brake would have the same or less wear than on a conventional car.
I recently enquired of Toyota UK about the details of the Prius braking system. Some of my comments have previously been posted but here goes again...
The Prius subsystem which handles braking is a blend of electric regenerative and conventional hydraulic technology.
As you tread on the brake pedal the system notes how you did so: how hard; and how suddenly. From this, it works out (very fast) what braking force is required. As much of this as possible is provided by regenerative braking; the rest of done by hydraulic braking (with the usual brake pads and such).
There are several useful benefits from this.
(a) If either of the available braking methods fails, the other continues to provide some kind of slowing force. If the electric side fails, I infer the hydraulic provides all of what's needed.
(b) Regarding your second question, I suppose that the brake pads experience less wear, because regenerative braking is essentially "non-contact" and will handle most of the low-force braking (such as gentle touches on the pedal).
You should realise that much of the Prius is conventional. What is new is how the old is blended with the new.
As an interesting side note, the dealer I work for has ONE recorded case of replacing brake pads on a Prius. I've seen some with well over 100k miles and over 50% of the pad lining remaining.
I don't know but a conventional parking brake is the easiest way. By the way, passenger cars do not have an "emergency brake." They are called a parking brake because they only apply the brakes to the rear wheels and will not stop a vehicle as quickly as the service brake.
The Prius does a good job of emulating a conventional automatic gearshift car. On the dashboard is a button which has the same effect as shifting the lever to Park. It locks the transaxle as usual and is strong enough for level ground. The knob to select [R]everse/[N]eutral/[D]rive (and new [B]attery-recharge option) is just below this button, with functions lined up in the same sequence as on a standard gear lever: imagine the arc which your hand moves through during operation of a standard shift; the same arc is followed in a Prius, just higher up at dashboard level.
Above the rest for your left foot is a easy-use foot brake that engages a very normal mechanical brake. Forget to disengage this and it obstructs your left foot; there is also a warning light.
But in case of hydraulic failure, the mechanical "parking" brake will still function as an emergency brake, correct? I've always called it an "emergency" brake for that reason, and I do practice stopping the car with it (comes from my training as a naval aviator, I guess).
Yes, in case of total hydraulic failure, the mechanical parking brake will still function as an "emergency" brake but stopping distances will probably be at least triple the distance with a normally functioning brake since the front brakes do most of the braking. Nothing like the stopping power of a tailhook though!
The B position is an engine braking function. Seems to me its only purpose is to help in long downhill runs, simulating a stick shift car using the engine to back down a little.
Not to be picky, actually it is touted as an optional instruction to the car to charge the battery using regenerative braking. The driver will be in a better position to know the road ahead so can tell the car to recharge (and, incidentally, slow down). Most of the time, I find this function of little use; but it's nice to be able to choose. As it happens, I do employ it most to apply some e-braking where foot-braking is not essential; but that certainly is not its primary function. Start relying on it and one day you may find the battery can't take more charge -- then braking won't be as hard as hoped and you suddenly have to f-brake anyhow.
At least, all of the above is based on recollections of a tedious trawl through the handbook, as well as general Toyota propaganda.
That can't be right. We all know that the Prius regenerates power whenever you back off the accelerator. The book also mentions that the B function shouldn't be used as a practice, because it will get poorer gas mileage. I see the only purpose as engine braking, but then I am a new owner (a week or so).
I question this explanation, and hope you can back it up with further references of your own or Toyota's. As I said above, I think there will be engine braking only when you are using the B function of the shift lever.
If you say not, I suppose that ends the discussion. ;-)
Not always. Oddly, I have managed to make the car freewheel by a very (NB) light touch on the brake, as well as by a similar touch on the accelerator. Mostly the car decides for itself whether or not to insist on charging the battery, or not doing so. Keep in mind, you are not the boss where such matters are involved. Have you noticed how many gauges are not provided in a Prius? (Such as engine rpm and temperature.)
That'll be because the overall efficiency of charging the battery then recovering the charge to drive the electric motor is smaller than the efficiency of driving the wheels more directly: either by the petrol (US:gas) engine alone or by the petrol engine via the generator driving the electric motor -- which happens more often than some people imagine.
I have a theory, yet to be tested, that one could actually obtain better mileage by the judicious application of a bit of welly: by forcing the car to drive directly from the petrol engine and/or "engine-->generator-->motor", one could cut from the loop the comparatively lossy battery. But that _is_ still just a theory.
Hang in there. And look into those manuals again. ;-) In the end, use it in whichever way works for you. Later versions of the technology will, I expect, enforce whichever practices have been found to be best.
Tip, FWIW: the rear lower storage area (ie, beneath the fold-up panels, where the spare tyre lives) can be made more useful by placing the (separate purchase) optional Toyota rubber mat over the spare. You can fold up the rearmost section of the panelling and sit small/medium coolboxs (up to tall enough for 2-litre soft drinks bottles) securely in the "slot".
If you caught my post of a day or two before the above, you may have seen I mentioned asking Toyota UK for technical data. They provided lavish documentation with diagrams, which prompted my synopsis and inferential explanation. If you have another, I'd be interested to hear it. If your objections are simply that you prefer not to believe (or you are trolling), I can't help you.
Welcome, Gary. I forescast ou'll be driving with a smile. I am.
In hilly terrain I use the B setting in lieu of braking on steep downslopes. Else, I leave it alone. The problem with using B for slowing in traffic is that it doesn't trigger the brake lights.
The hypnotic energy-transfer animation shows that even on level ground the gas engine periodically charges the main battery. The book's advice against using B applies to travel on level ground where indeed the practice does reduce the gas mileage.
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