Dynamic cruise issues

Discussion in 'Prime Technical Discussion' started by RobertZ, Aug 9, 2018.

  1. RobertZ

    RobertZ Junior Member

    Joined:
    Jan 14, 2018
    38
    40
    0
    Location:
    Nashua, NH
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    This is for my 2017 Prius Prime, Premium model.
    DynamicCruiseControl works fine most of the time but I had few close calls.
    More than one time on a clear sunny day I am driving on a highway (50-70 MPH) range.
    Following other car with 1 car distance set.
    When other car slows down (not a sudden stop), my car does not slow down quickly so it ends up flashing panic BREAK warning and I have to press the break myself as I don't trust car will stop in time.
    Today I had to slam on the break as if the cruise was off.
    That's another point when the dynamic cruise is working is there an indicator?
    I don't meant that it's ready for radar, I mean it's actively going to break the car or not!
    It's not the case that all of my close calls the DCC was off. It was ON.
    I am only doubting the last instance that may be I had tap the break before that.
    I always pay attention but this is getting scary!
    Has anyone seen this behavior?
     
  2. Bob Comer

    Bob Comer Active Member

    Joined:
    Sep 20, 2010
    499
    309
    0
    Location:
    South Carolina low country
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    I never trust it to brake. It may by itself if I'm not attentive enough, but I'm not going to watch it panic stop/hit something if I can help it.
     
  3. wfolta

    wfolta Active Member

    Joined:
    Jun 13, 2009
    365
    145
    0
    Location:
    Washington DC
    Vehicle:
    2018 Prius
    Model:
    IV
    I haven't had the DCC act like this on our 2018 Prius. You've probably thought of these things, but to throw out everything that comes to mind...

    You say "doesn't slow down quickly", does it slow down too slowly, or not at all?

    I'm pretty sure that if the DCC is active and sensing the car in front of you -- and hence should slow when it does -- you'll see the other-car image in the display. If you don't see the other-car, it doesn't know it's there. As you say, if you tap the brake solidly, you turn CC off, and of course if you're pushing on the gas you override it as well. (Your floor mats are anchored well and not touching the gas, right?)

    Holding the button down long will switch from dynamic to non-dynamic CC. Assuming you're not accidentally doing that.
     
  4. VTBIGDOG

    VTBIGDOG Active Member

    Joined:
    Dec 21, 2016
    167
    120
    0
    Location:
    USA
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    "More than one time on a clear sunny day I am driving on a highway (50-70 MPH) range.
    Following other car with 1 car distance set."

    60 MPH is 88 feet/sec. If you are 20 feet from the car in front of you at that speed, you are a little more than a 1/4 second behind. You should be several seconds behind. Neither the system nor your right foot could react quick enough to maintain that close range if the car in front of you merely backs off the accelerator. Increase the interval and the system will work properly.

    When the person you are tailgating looks in the rear view mirror and can count the fillings in your teeth, you may encounter the infamous 'brake check' so leave an adequate space and you should be good.



    Posted via the PriusChat mobile app.
     
  5. Old Bear

    Old Bear Senior Member

    Joined:
    Sep 15, 2017
    394
    625
    19
    Location:
    Boston, Massachusetts USA
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
    Yes, there is an indicator in the MID but it's not very prominent. It's small and way over on the lower far right in a location more easily seen by a front seat passenger. It's green and I believe it's only visible when the ACC is set and in operation.

    ACC-symbol.jpg MID-display-indicators.jpg

    Quoting from an article by Bill Howard in ExtremeTech dated July 7, 2016:

    ACC just disengaged and you don’t realize it. In heavy traffic situations, you may drive with your foot hovering over the brake because the fool in front of you might brake harder than ACC can slow the car. You may subconsciously tap the brake, not realize it, and believe ACC is still maintaining a safe distance from the car in front — except it isn’t. Somewhere in the instrument panel or head-up display is an indicator to show ACC is engaged, but it’s easy to miss. Typically, cars with ACC also have forward collision warning if you get too close, and sometimes that latter system invokes automatic emergency braking. Some drivers may wish for an algorithm that says, “In heavy traffic, if the driver taps the brakes, then disengage the throttle, but keep active the braking/slowdown part of ACC.”
    My previous car's heads-up display showed the current speed along with "cruise control engaged" and the set speed. It's unfortunate that Toyota did not do something similar.
     
  6. sam spade 2

    sam spade 2 Active Member

    Joined:
    Mar 31, 2018
    897
    435
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    THIS.

    But.....I have found with a similar system in my Fusion, when you do touch the brake pedal, it cancels the cruise control COMPLETELY. That is, if it was slowing down at the time, it STOPS all braking activity and makes it appear that you are suddenly speeding up. :eek:

    This can scare the crap out of you if you are close to the car in front when it happens.

    So.....if you are going to take over manual control while the DCC is slowing down, don't baby it; engage that brake don't just tap it.
     
  7. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

    Joined:
    Oct 17, 2010
    29,316
    18,563
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    I don't think there is a "one car distance" setting? There's three settings IIRC, and they would all invoke some sort of "seconds" rule, ie: both distance and speed.

    Yeah radar cruise bothers me too, for the same reasons:

    1. Do you really trust it? If it's got you stressing, wondering if/when it's going to brake, that's not good.

    2. Is it currently on? Or not...

    A work around: use the most conservative following distance setting?
     
  8. Lucifer

    Lucifer Senior Member

    Joined:
    Aug 23, 2015
    1,011
    469
    0
    Location:
    Nh
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
    At above 50 I always use the three car space, driving at 65 with one car space is going to make for sudden panic stops by the car.
     
  9. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

    Joined:
    Oct 17, 2010
    29,316
    18,563
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Seconds of following distance are more intuitive, work at any speed. If you use the 2 second rule, and considering the average car length*, you would want to have over 9 car lengths (equiv. to your car "space"?) at 50 mph.

    How many seconds is debatable as well. Washington state troopers recommend 4 second following distance on highways, here:

    Is it a 2, 3 or 4-second rule for following on a highway? | Road Warrior

    Some calc:

    upload_2018-8-10_7-20-40.png
     
  10. RobertZ

    RobertZ Junior Member

    Joined:
    Jan 14, 2018
    38
    40
    0
    Location:
    Nashua, NH
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Thank you all for the feedback.
    No I am not purposely tailgating the car but based on the feedback I might set it to 3 car lengths for anything above 50 MPH.

    Fusion example didn't apply, as mine does not accelerate, it's just too slow acting at faster speed to safely stop and me setting it at 1 car length didn't help.
    You would think Toyota had figured this safety issues in the algorithm?
    Lack of indicator is bad (yes I know about the cruise setting on the right) because only way you know it's working is when car decelerates.
    The radar shows the presence of the car in front of you but that display cycles through many other things so it's not a reliable indicator.
    They need readout that stays on like "DCC ON" and "DCC OFF".
     
  11. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    38,070
    9,319
    40
    Location:
    Canada
    Vehicle:
    2010 Prius
    Model:
    N/A
    Yeah I never use 1 bar on the highway. It’s too close for comfort. Just FYI it’s not “1 car” or 3 car” lengths. The bars just represent the “short”, “medium” and “long” distance setting. Actual distance depends on speed so 3 bars at 70mph is different than 3 bars at 40mph.
     
    breakfast, benagi and Mendel Leisk like this.
  12. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

    Joined:
    Oct 17, 2010
    29,316
    18,563
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    The one, two and three bar settings likely equate to some number of seconds of following distance, say for example two, three and four seconds. This would obviously vary with speed, but the seconds stays roughly constant.

    Two-second rule - Wikipedia
     
    #12 Mendel Leisk, Aug 10, 2018
    Last edited: Aug 11, 2018
    Tideland Prius likes this.
  13. CraigCSJ

    CraigCSJ Active Member

    Joined:
    Sep 2, 2004
    252
    122
    0
    Location:
    San Bernardino, CA
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    I believe that if you press the right side steering wheel button four times to the right from the hybrid syenergy display, the display will show if dynamic cruise control is activated, the distance setting, whether it is following a car ahead, and the speed set. This display is like the pop-up window but stays visible all the time.
     
    breakfast likes this.
  14. t_newt

    t_newt Junior Member

    Joined:
    May 27, 2018
    25
    33
    0
    Location:
    94087
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    I have a 2017 Prius Prime and use the dynamic cruise control all the time when I'm on the freeway. I use the 1, 2, or 3 bars setting depending on how packed the traffic is. If you use 3 bars and traffic is packed, cars will just constantly change lanes into the spot in front of you. They won't let you have that big a space no matter how much you might want it.

    I've never had a problem with it braking, even braking hard, when traffic speed suddenly slows down. Nevertheless, as has been mentioned, if traffic is packed together at high speed, then you don't have much leeway for mistakes, and you really need to pay attention and be ready to take over on a moments notice.

    Despite this, as long as traffic isn't too crazy, I find driving with the cruise control more relaxing than without it. It allows me to look further ahead to anticipate traffic changes.
     
    breakfast likes this.
  15. RobertZ

    RobertZ Junior Member

    Joined:
    Jan 14, 2018
    38
    40
    0
    Location:
    Nashua, NH
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Hi All,
    I was hoping that if bar setting keeps distance based on the speed (which makes sense) then it should really keep SAFE distance at 70MPH.
    But it's not doing that at 1 bar.
    I did experiment with 3 bar setting and that resulted in no panic stops.
    Perhaps this should be a warning or automatic change of bars to 3 if speed goes above 60MPH?

    I agree that in heavy traffic 3 bars will leave open space for people to cut in all the time. In those cases I just cancel the cruise.
    CraigJS yes I found that setting. However I hate to give up that display for other information, instead an indicator elsewhere would be nice.
     
  16. breakfast

    breakfast Active Member

    Joined:
    Feb 18, 2015
    251
    175
    0
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    I know I'm piling on (I started my reply much earlier but forgot to post it, so everything below has already been said), but there's your problem.

    Why on earth would you be traveling (let's say Route 3 or the Everett Turnpike) 50-70 MPH with 1 car distance set? Are you some evil tailgater with a deathwish? ;)

    I drive on crazy interstates where it goes from 70 to zero in a flash, and there's no *way* I would trust 1 bar while traveling that fast.

    My rule of thumb:

    Fast moving highway traffic (55 to 75 MPH) - use 3 bars on dynamic cruise

    Slower moving highway traffic (say average speeds on the road 50 or less, or the first slowdown has already happened, or traffic between 50 and 65 where the traffic is heavy enough that a street racer type can't weave around everyone going 90) - 2 bars

    Only in true bumper to bumper traffic do I use 1 bar --- but even in those cases I typically use two.

    --

    As for the indicator you are asking for about whether radar cruise is active, it's there - if you have the normal "hybrid system indicator" showing to the right of the spedometer, keep pushing the right side steering wheel "four-way joystick" to the right until you see the radar cruise icon full time (should be four button presses to get there... it's the fifth icon from the left in this picture from the owner's manual)

    Screen Shot 2018-08-15 at 9.29.03 AM.png
    The screen will look like this:
    Screen Shot 2018-08-15 at 9.30.31 AM.png
     
    #16 breakfast, Aug 15, 2018
    Last edited: Aug 15, 2018
    Old Bear and Tideland Prius like this.
  17. Ralith

    Ralith Junior Member

    Joined:
    Jun 15, 2014
    44
    17
    0
    Location:
    Bloomington, IN
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    There is a radar cruise and normal cruise icons when they are on and then the "SET" icon comes up when they are actively controlling speed

    Just got my Prius Prime Advanced, but I drove it back home 900 some miles.
    Cruise control worked great, I agree at high speeds short distance is too short for me, but other people will still cut in front or me so that's life. I will use 1 if it's relatively light traffic just for safey if someon cut me off. I usually run on medium, as long is really far and starts slowing me down before I would go around someone.
     
Loading...