Should a Prius roll backward at a stoplight??

The Prius has a hill-holder feature that attempts to keep it from rolling backwards when in D. It works pretty well, but does have its limits on very steep hills, where you will get some backward roll.

Tom

 

When at a stop, using the brakes to hold position appears to turn off this current. I'm using a Graham scanner and can see the current disappear when the brake is held and the car stopped. If you maintain position on a gentle slope while stopped, the car will be drawing current but holding it with the brake stops the current.

When I'm stopped on a flat section, I'll often put the car in "N" to allow taking my foot off the brake. When the light changes, I slip into "D" and drive off.

I need to go back and check if using the parking brake has the same effect as holding with the brake pedal.

Bob Wilson

 

Well, I just returned from a vacation in Seattle. The Impala that I rented there rolled backward big time when stopped on a hill. You are not alone.


Dave

 

<div class='quotetop'>QUOTE(bwilson4web @ Nov 12 2007, 01:30 AM) [snapback]538239[/snapback]</div>

Please don't do that. I was once bumped into by a fellow who thought that the ground we were stopped on was flat enough, and did not notice as he slowly rolled into me. Nobody ever thinks they can make a mistake like this until they do.

 

<div class='quotetop'>QUOTE(Tideland Prius @ Nov 12 2007, 01:44 AM) [snapback]538146[/snapback]</div>

The Prius doesn't just mimic creep, it has a specific hill-start function to hold position. But as others have said, there is a limit to how much torque it will apply to prevent backwards motion. ("Backwards" being forwards if the transmission is in R).

The creep and hill-start functions are deactivated by sufficient pressure on the brake pedal. How "sufficient" is defined, I'm not sure - I originally thought it was the brake-light relay, but it's not that simple.

 

The amount of creep torque varies depending on how fast you're
drifting in the *opposite* direction. To really get a feel for
this, find an isolated area in a parking lot and let the car drift
backward at about 2 mph and then put it in Drive. If you're not
over the protection threshold when it just beeps and goes into
Neutral, you'll feel a HUGE surge of torque until you stop and then
the normal creep thereafter. The motor sensors are very fine-
resolution and the hybrid computer knows exactly what's going on.
So hill-holding is a variable thing, and equates more to "let us
roll *very* slowly back down the hill" rather than a hard hold but
still plenty of help while moving your foot.
.
_H*