Unable to reset to higher speed in DRCC

Discussion in 'Prime Technical Discussion' started by srivenkat, Oct 2, 2020.

  1. srivenkat

    srivenkat Active Member

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    Hello All,

    While using DRCC, I find that if I set my initial speed to say 50MPH and later accelerate to say 60MPH and try to set that as the new speed by pushing down to SET, it doesn't take effect. This is contrary to my experience on many other Toyotas with regular/traditional cruise control. Anyone else has noticed it?

    Thanks.

    EDIT: Improved clarity.
     
    #1 srivenkat, Oct 2, 2020
    Last edited: Oct 2, 2020
  2. schja01

    schja01 One of very few in Chicagoland

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    Once the system is engaged moving to stalk up then releasing moves it up 1 mph if you hold it it’ll continue to increase about 1 mile an hour per second or so moving the stock down decreases a speed 1 mph per Push or hold it and it’ll continue to take the speed down about 1 mph per second.
     
  3. Bob Comer

    Bob Comer Active Member

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    That's definitely how the prius does it in the 2 priusses I have owned -- if the cruise is already on, the same action as set changes the cruise target 1mph different from what it originally does. If you want to accelerate 10MPH, push up on the stock 10 times. (or disengage the CC, then accelerate, then set. (what a pain. :)
     
  4. srivenkat

    srivenkat Active Member

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    On the 3rd Gen Prius I used to have, as well as my Camry Hybrid and pretty much all other cars I have driven, I could set the cruise speed higher by accelerating (using the pedal) to the higher speed and pushing down on SET again, and I find this isn't happening in my Prime while using DRCC.
     
  5. Bob Comer

    Bob Comer Active Member

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    I'm pretty sure my gen 3 prius acted the same as my prime. Maybe it's a DRCC vs. CC issue as my Gen 3 had DRCC also.
     
  6. Salamander_King

    Salamander_King Senior Member

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    I can't remember how my Gen3 with just regular CC worked, but on PRIME definitely, @schja01 gave you the right answer. Once set, push the stalk up will speed up, but down which is the set will decrease the speed. If you want to set at a new higher speed, you have to first cancel the DRCC by pulling the stalk and then set it at the new higher speed.
    upload_2020-10-2_13-46-3.png
     
    #6 Salamander_King, Oct 2, 2020
    Last edited: Oct 2, 2020
  7. srivenkat

    srivenkat Active Member

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    I am aware of the 1MPH increase/decrease and use it often. It's the other way that I often also used to reset to the higher speed using the pedal and SET that's not working.
     
  8. schja01

    schja01 One of very few in Chicagoland

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    You can engage it without the radar dynamic function and it will work as normal Prius do. To engage in dumb mode press and hold the stalk button until the confirmation message is displayed.
     
  9. Tideland Prius

    Tideland Prius Moderator of the North
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    I've only experienced DRCC in Prius (Gen 3, 4, Prime) and that's how it works. I assume it works the same way on other Toyotas with DRCC.

    The method you're describing is Toyota's regular cruise control.

    For DRCC, you'll have to have to increase the set speed manually. Now, in Canada, we have option of 5km/h increments. There was that option (5mph) in the Gen 3 but I believe it was taken away for Gen 4 in the US version because of complaints.
     
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  10. srivenkat

    srivenkat Active Member

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    Yes, that's what I meant to mention in my original post (which I have clarified in it just now), that the behavior I have seen with regular CC isn't working in DRCC (Prime is the first vehicle for me with DRCC). I wonder why DRCC doesn't allow reSET after pedal acceleration like it does in regular CC.
     
  11. Tideland Prius

    Tideland Prius Moderator of the North
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    I suppose it's because Toyota didn't want to have two different but similar buttons or controls on the stalk (But now that Toyota has moved from the stalk to a button layout for cruise control, maybe they can have separate functions?)

    But the idea is that you are still changing the set speed. The difference is that now the radar controls the speed since it also controls the distance to the vehicle in front, vs. conventional CC where it doesn't know its surroundings and can only respond to the change in set speed command from the driver.

    And that trickles down to the SET function.
     
  12. alinica2001

    alinica2001 Member

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    How do you enable this option ? Via techstream ? I have a C-HR hybrid ( european version ) which does that 5 km/h increment and I would like to do the same on my Prime.
    Thanks!
     
  13. Tideland Prius

    Tideland Prius Moderator of the North
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    I'm not sure actually. Maybe @Elektroingenieur might know?
     
  14. Elektroingenieur

    Elektroingenieur Senior Member

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    The Repair Manual (more info) doesn’t mention any customizable parameters for cruise control behavior.

    The System Diagram page for the Dynamic Radar Cruise Control system says that the driving support ECU assembly receives a “Country specification information signal” from the main body ECU, which has different firmware for each destination country. I imagine this is how the large adjustment increment is determined (Owner’s Manual (PDF), page 397).
     
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  15. Tips

    Tips Member

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    Cruise control on the Prime is a handfull too learn. I thought I had the good old stuck throttle issue. But after 6 mths. I finally mastered how it works, but it was a handful. You will master it in time. Just know how too turn it off! And another thing don't use it when you are in heavy trafic. You will like it once you get it. Check the manual and read it lots as it is confusing as well

    Posted via the PriusChat mobile app.
     
  16. PiPLosAngeles

    PiPLosAngeles Senior Member

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    What's more fun for me is that the speed set on the DRCC and the speedometer get out of sync. Very often I will have it set for 65 and the speedo will read 64 for a prolonged period. Then, bumping it up once gets the speedo to 66. I suspect there's some kind of internal rounding error converting kph to mph.
     
  17. Elektroingenieur

    Elektroingenieur Senior Member

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    Mine does this, too, and I explained why in a previous posting.
     
  18. PiPLosAngeles

    PiPLosAngeles Senior Member

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    The chance to do some science! Luckily it will be straightforward to test these hypotheses. We should observe distinctly different behavior depending on which hypothesis is correct. If it's due to hysteresis control, the phenomenon will be equally likely to occur at all possible speed settings. If it's due to unit conversion errors there will be some speed settings where it's more common than other speed settings.

    A simple test would be to try the following DRCC speed settings and keep track of how often the car settles into cruising 1 mph below the set speed:
    • 61 mph
    • 62 mph
    If it's hysteresis control measures 61 or 62 mph setting should make no difference in how often the car ends up cruising 1 mph below the set speed. However, if it's due to conversion error 61 mph will be approximately 3 times more likely to fall to 60 mph than 62 mph is to fall to 61 mph.

    I had composed a very long explanation of why, but decided against it.
     
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  19. Salamander_King

    Salamander_King Senior Member

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    Interesting. Let us know what you find out. I currently have no occasion to use DRCC. I will not be able to do the experiment myself.
     
  20. jerrymildred

    jerrymildred Senior Member

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    This explanation makes the most sense to me. And it applies to regular cruise just as much as DRCC. If the system tries to hold the speed too precisely, it'll burn a lot more fuel making frequent, abrupt throttle changes than the infrequent and gradual ones used it just keeping it close. Our speed controls and oven burners worked the same way in can making. So do house thermostats. In fact, we replaced our previous one because it was too precise for my taste and making the air conditioner cycle on & off too often. The new one lets you set that dead band. Less wear and tear on the compressor with fewer starts but longer runs.

    Still, if I set the cruise for 60, it'll sometimes want to run at 59 and sometimes at 60, bit I don't think I've ever seen it want to run at 61. I suppose that it's just configured to be a little offset to the low side.
     
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