Brake delay

Discussion in 'Gen 4 Prius Main Forum' started by Chippingawayatlife, Jun 30, 2017.

  1. Chippingawayatlife

    Chippingawayatlife Active Member

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    Does anyone notice if the brakes on the Prius have a slight delay to them when moderate to high brakes are suddenly applied? Perhaps it's delayed when switching from gas to brakes suddenly.
    I've had three occasions this has happened now. On my 2016 Prius eco without TSS and driving exclusively on pwr mode, I've slammed on or moderately hit the brakes only to find that the brakes kick in slightly delayed. I found the situations slightly dangerous and very embarrassing.

    On the first instance, it was about 8 months ago, about 2 weeks after I bought the car. I think I posted this near miss on PC too. I was on the highway probably going about 50mph cruising with my foot slightly on the throttle. I think the ICE was off. A stopped car suddenly changed lanes into my lane but wasnt accelerating fast enough. I still had plenty of room in front, but hit the brakes fairly hard, slowing quicker than I expected. Thinking back at it now, there was probably a slight delay in the brakes that caused me to hit the brakes a bit more because I didn't get any brake feedback as I was closing in to the car in front.

    On the second instance about 2 months ago, I was about to change from a stopped lane to a moving lane (same area as the first instance, but I'm the stopped car changing lanes haha). From a stop, I creeped out a bit, then noticed that I didn't turn the wheel enough so I hit the brakes suddenly while turning the wheel more. I noticed that the car didn't stop, and by that time, I had turned the wheel enough to get enough clearance from the car in front so I smashed on the gas to go. With my foot on the gas, the brakes suddenly grabbed hard bringing me from maybe 8mph to near 0mph very quickly. At this point I let off the throttle pretty confused and embarrassed. That all happened in maybe 2-4 seconds. It was jerky and felt like how it feels to stall a manual transmission car on 1st gear.

    Today I had another instance of indecision. When coasting downhill to a light at 45mph, the light turned yellow. I could borderline make it, so I smashed the throttle. The engine took its typical time turning on so I didnt have enough power. At this point I was coming close so I needed to stop, but with plenty of room. I quickly switched to medium brakes but noticed that I got nothing. Then I pressed a little more, say medium/ hard because I still had plenty of room. The brakes suddenly grabbed hard that the antilock brakes were activated and my car direction was a bit squirly. This happened until about 15mph, when I let loose the brakes a bit so I slowly reach the stop light, still 5 car lengths away.

    I don't have sudden stops much with this car, so maybe im not used to the Prius behavior yet. I think I recall my old cars brakes having less of a delay where stop means stop. I think these instances of brake delay might be due to my indecision. Maybe MG1 goes from starting the ICE to reversing for Regen? Maybe it has to do with software priming the brakes? But I also feel the throttle lag is causing some of my non-commitment. I don't think this is exclusive to the car, as the delay is so slight. I feel it's slightly my fault and that I'm not used to the Prius. Does this sound normal to you guys?
     
  2. alanclarkeau

    alanclarkeau Senior Member

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    I suspect your last paragraph might be ONE key. With other cars, you take a bit of time to fine-tune your reactions, but soon are able to predict, because you're applying the brakes regularly.

    ANOTHER key - using DRCC a lot means that you just don't touch the brake pedal often. One of my regular commutes, if there is a car in front, I won't touch the brake in 21km except as I reverse out of my driveway and as I park at the other end. My previous car, would be dozens of times.

    THE other key - and I suspect you've hit on it above, is that there are at least 4 different braking systems - the hydraulic, regenerative, DRCC's own braking (mainly using REGEN) and Emergency braking.

    PLUS - there is the way it primes the brakes for greater braking force if it detects that a collision is imminent. If it's done that, I find the braking is quite savage.

    I've had the car for a year (yesterday), and I wouldn't say I'm really used to them yet.
     
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  3. robsnyder20

    robsnyder20 Active Member

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    My first Prius as well, and I can say even though I rarely hit the brakes HARD, there almost seems to be a delay, then the car will practically throw you into the windshield when the brakes catch. When you need to hit the brakes, it seems to have more delay than I would like for 100% braking force. I will say the car stops way faster than my last toyota without ABS, stability, and all those extra safety features.
     
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  4. pakitt

    pakitt Senior Member

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    The Gen4 brakes much more than the Gen3.

    In all cars with ABS, BTW, when you brake you need to brake hard, or it will not work properly.

    That being said, the Gen4 uses regen more aggressively than Gen3, and the fact it is using regen first than brake pads if you don't brake decisively, might play a role for you.

    I would like to correct one statement of alanclarkeau - there is one braking system, 2 braking technologies (hydraulic + regen), 3 different systems that access them (the driver, the DRCC, the emergency braking - the last 2 activating the brakes indipendently of user intervention).
    I have to say that emergency braking and DRCC sometimes are quite strong if not sudden (especially the former).

    So far I have had no problem with the braking power or the braking system so far.

    If you think there is a slight delay, either you need to adapt your braking habits and brake more, or get your brakes checked in case there is actually something wrong.

    Again, this car can brake quite effectively, given you push the pedal brake with intent.
     
  5. alanclarkeau

    alanclarkeau Senior Member

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    With braking systems - I thought I read somewhere that emergency braking is solely hydraulic? Whereas DRCC is only hydraulic if REGEN doesn't meet the need? Would that be right?
     
  6. pakitt

    pakitt Senior Member

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    I think emergency braking does that - directly hydraulic by pre-loading the pressure brake pump.
    Instead DRCC simply "brakes" and the system brakes according to necessary braking force requested by the system.
     
  7. wrprice

    wrprice Active Member

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    FWIW, I've always been impressed with the Prius braking response in panic situations. Gen2, 3, and 4. I suggest you take the vehicle and find a lightly travelled, straight road where it would be safe practicing a hard/panic stop. Get up to 30-40mph, make sure your seatbelt is worn properly, and then step on the pedal hard and fast. You shouldn't notice any hesitation. If you do, take the car for service.

    I do that test on every test drive now. My Gen2 shipped from the factory with an imbalance in the hydraulic brakes, which only became apparent when I had to do a hard braking avoidance manoeuvre on the highway and the car pulled hard to the left. Dealer fixed it under warranty.

    During light to moderate braking, I can feel the transition from regen to hydraulic braking around that 6-7 mph range. Some people interpret the sensation as the brakes "not working" for a moment. What really happens is you're still slowing, but the braking force doesn't increase (neither does it decrease) for just a moment until the pads engage. I think it was more pronounced on Gen2, but it's still there on Gen3/4. If you're feeling this in a quick-stop situation, though, either there's something wrong or you're not pressing firmly on the pedal.
     
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  8. FuelMiser

    FuelMiser Active Member

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    Something about your post, especially the sentence above, makes me think you are using your left foot to hit the brake pedal while your right foot stays on or near the gas pedal. If I am wrong, please accept my apology and disregard the rest. First of all, I have never experienced the delay in braking you describe, and I've had two "panic" braking incidents where ABS activated. I'm very impressed with panic braking in this Prius. But if you are on or near the throttle while applying brakes, Prius does include some logic to prevent "unintentional acceleration" incidents that occurred back in Gen 2 days that could explain the symptoms you describe. Prius does not like it when you apply brakes and accelerator at the same time, so best to use a single foot for these operations.
     
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  9. Chippingawayatlife

    Chippingawayatlife Active Member

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    Thanks everyone.

    I'll try to play with the brakes in an empty parking lot to see how the car reacts under hard braking and gas-then hard braking. I'll try it with my civic or Camry too. But I think you're all right, the Prius brakes with great force, much better than I anticipate.

    I'll answer some of your questions. I did not do any left foot braking. My car does not have TSS (LDW, DRCC, collision warning).
     
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  10. wrprice

    wrprice Active Member

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    I don't think TSS would play into this much, even if you had it. It can anticipate and pre-load the brakes or even apply them automatically in some situations, but you're describing driver "normal" braking input.

    Gen4 under normal circumstances should behave the same with/without TSS, and in my experience similar to previous generations without TSS. TSS is a nice feature, but it doesn't change how the car handles.
     
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