My Prius jumps off the road!

[swfoster2]

Has anyone ever had this? (If a thread already exists, sorry)

When I am slowing down approaching an intersection, if the road has bumps or potholes, the car literally jumps off the road a little. It has happened a few times, but last night it really jumped. I was heading south on La Brea approaching Santa Monica Blvd in the right lane. (Target). I was preparing to turn right onto Santa Monica. That part of La Brea has alot of bumps and potholes. Since it's downhill, I was in total EV (about 20 mph)and I had slowed a bit, but then accelerated a little, and it was like the car left the ground momentarily after it hit a patch of bumps. Some of the wheels were actually turning in the air! When it came back down it took me a split second to right its course since the wheels landed at different points. I wasn't worried because it was actually kinda funny. But it was by far the weirdest thing I have had happen yet. No matter- this car rocks

[kdailey356]

i would'nt consider this fun, my car does this when i drive over a metal sewer cover, or pot holes.. this effect is cause by the traction control being activated.

[dogfriend]

Actually, if you are braking, its not the traction control that causes the "jumping" but it is when the regenerative braking "gives up" or releases so that the ABS can be activated. The ABS can only work with the "regular" brakes, so the regenerative braking cannot be used at the same time as the ABS.

[swfoster2]

<div class='quotetop'>QUOTE(CapeCodPrius @ Nov 11 2007, 11:42 PM) [snapback]538214[/snapback]</div>

i would'nt consider this fun, my car does this when i drive over a metal sewer cover, or pot holes.. this effect is cause by the traction control being activated.
[/b]

So this is supposed to happen? It never struck me as being dangerous because the car snaps back so quickly. But, now I know to expect it so I can compensate. No other car I have ever driven has done this. Is this just the Prius or does any car that has traction control do this?

[qbee42]

<div class='quotetop'>QUOTE(cheminee @ Nov 12 2007, 01:59 AM) [snapback]538251[/snapback]</div>

So this is supposed to happen? It never struck me as being dangerous because the car snaps back so quickly. But, now I know to expect it so I can compensate. No other car I have ever driven has done this. Is this just the Prius or does any car that has traction control do this?
[/b]

Normal braking on the Prius is done with only the front wheels. This is because the braking is regenerative, in that the energy is converted into electricity for the battery. If the front tires lose traction, then the control system reverts to hydraulic braking on all four wheels. Hydraulic braking is also engaged when the speed is too low for regenerative actions (about 8 mph), in a panic stop, or any time the battery can no longer accept charge.

Tom

[Sarge]

<div class='quotetop'>QUOTE(qbee42 @ Nov 12 2007, 11:57 AM) [snapback]538442[/snapback]</div>

Normal braking on the Prius is done with only the front wheels. This is because the braking is regenerative, in that the energy is converted into electricity for the battery. If the front tires lose traction, then the control system reverts to hydraulic braking on all four wheels. Hydraulic braking is also engaged when the speed is too low for regenerative actions (about 8 mph), in a panic stop, or any time the battery can no longer accept charge.
[/b]

Tom, I was actually wondering about this exact idea a few days ago. A question for the Prius gurus around here...

To my knowledge, in many modern cars, 'regular' braking is done by all 4 wheels (with varying degrees) to be more stable as the car decelerates. My understanding of regenerative braking on the Prius is that the friction brakes are not used at all and the electric motor is what slows the car under normal braking.... which means only the front wheels provide braking action.

If this is truly the case, shouldn't the car theoretically tend to "nosedive" more than a regular car using 4-wheel braking? I have not noticed this, but based on my (admittedly limited) understanding of physics, I would think this should be the case...? Or is there actually some braking being performed by the rear drums during regenerative braking?

Hmmm...

[okiebutnotfrommuskogee]

<div class='quotetop'>QUOTE(cheminee @ Nov 12 2007, 12:59 AM) [snapback]538251[/snapback]</div>

So this is supposed to happen? It never struck me as being dangerous because the car snaps back so quickly. But, now I know to expect it so I can compensate. No other car I have ever driven has done this. Is this just the Prius or does any car that has traction control do this?
[/b]

The Honda Civic Hybrid that I used to have did a similar thing. If you were stopping and went over a bump or something that made one of the front wheels leave the ground for an instant, the regenerative braking cut off and the car seemed to momentarily surge forward until the driver pressed the brake peddle harder. The first time or two caused some concern, after that it was just a normal thing.

[qbee42]

<div class='quotetop'>QUOTE(Sarge @ Nov 12 2007, 03:39 PM) [snapback]538534[/snapback]</div>

Tom, I was actually wondering about this exact idea a few days ago. A question for the Prius gurus around here...

To my knowledge, in many modern cars, 'regular' braking is done by all 4 wheels (with varying degrees) to be more stable as the car decelerates. My understanding of regenerative braking on the Prius is that the friction brakes are not used at all and the electric motor is what slows the car under normal braking.... which means only the front wheels provide braking action.

If this is truly the case, shouldn't the car theoretically tend to "nosedive" more than a regular car using 4-wheel braking? I have not noticed this, but based on my (admittedly limited) understanding of physics, I would think this should be the case...? Or is there actually some braking being performed by the rear drums during regenerative braking?

Hmmm...
[/b]

It is true that only the front wheels are used during regenerative braking. Physics shows that a car braking with only the front wheels will show no more tendency to nose dive than one braking with all four, assuming all other factors are equal. What will be different is the absolute limit of braking performance. If the forces on the wheels were all equal, half the number of wheels would equal half the braking force. Of course the forces are not equal, and the front wheels contribute more to forward braking that the rear, but still the absolute braking limit is reduced by using only the front wheels. There is also a limit to how much electrical power the Prius can make and use during braking. This is why the control system switches to friction brakes in the event of a panic stop.

Tom

[mjms2b]

<div class='quotetop'>QUOTE(cheminee @ Nov 11 2007, 08:05 PM) [snapback]538195[/snapback]</div>

Has anyone ever had this? (If a thread already exists, sorry)

When I am slowing down approaching an intersection, if the road has bumps or potholes, the car literally jumps off the road a little. It has happened a few times, but last night it really jumped. I was heading south on La Brea approaching Santa Monica Blvd in the right lane. (Target). I was preparing to turn right onto Santa Monica. That part of La Brea has alot of bumps and potholes. Since it's downhill, I was in total EV (about 20 mph)and I had slowed a bit, but then accelerated a little, and it was like the car left the ground momentarily after it hit a patch of bumps. Some of the wheels were actually turning in the air! When it came back down it took me a split second to right its course since the wheels landed at different points. I wasn't worried because it was actually kinda funny. But it was by far the weirdest thing I have had happen yet. No matter- this car rocks
[/b]

I've noticed the same thing, usually in predictable circumstances. I try not to get too hung up on the specifics, but I know that the car is just doing it's thing. Being different is fun!!

[ACORNBLUES]

The acceleration sensation is relative. When the rear brakes engage, the angle at which the car decelerates changes. "jumps off the road"? Please.