I was just wondering if someone could explain why the Prius seems to "jump" or gain momentum when I go over an unexpected large bump or pothole? I have not owned the car during a Chicago winter yet, and was thinking today (after I experienced aforementioned jump) about how this could be troublesome.
It did not gain momentum, it just did not continue loosing it at the same rate. Basically your deceleration decreased instead of staying constant. This is the regenerative braking kicking off and switching to friction only braking. Same thing happens if you brake really really gently up until 7mph (in a GenII, not sure of the speed in a GenIII where regen kicks off). Human perception however "feels" acceleration, but it isn't. You just are prepared to keep slowing down at the same speed so you brace for it, but when the acceleration changes unexpectedly, it is as if it is all relative to the acceleration you were at, not 0. If that makes sense.
Adding to the general discussion above, the technical term for what you feel is "jerk", which is the rate of change in acceleration. Your acceleration quickly changed, but not your velocity, which is due to momentum. Acceleration is the second derivative of displacement with respect to time. Jerk is the derivative of acceleration, which makes it the third derivative of displacement with respect to time. Tom
Thank you for your very insightful answers. As for the software update, mine was built in February 2010, so I assumed that it came updated (and the dealer assured me it did). Perhaps I should look into this.
^ Yes do... ask the dealer to confirm if the software update has been applied. If it was not applied, it should help lesson the "jerk".
It is really a useless update created to satisfy the media... I would imagine next time you take it in for an oil change, they will either mention it or not. I wouldnt go out of my way for it...
As mentioned above. This is an "undocumented feature" of Prius and many other hybrids. The "software fix" only -reduced- the effect. It didn't eliminate it. It's there to prevent damage to the HSD in the event of high impact drive torque. You -DON'T- want to eliminate it entirely. It won't bother you in winter any more than in summer. In fact probably less, because you will (should) be braking earlier in winter.
I've had it happen to me once (quite a quick little adrenaline rush too) and I've not forgotten it. I figured that I should adjust my driving behavior a little to account for it (such as following a little further behind cars in front of me, braking a little sooner, etc). Although, if I drive any further behind people, I'll be posting about being on the receiving end of a road rage incident (does the whole friggin' world tailgate?)
I am with you with the belief that the whole world does tailgate. Makes for a very unpleasant commute.
As is also well documented, the Prius seems to induce road rage in tailgaters.................. must be out of jealousy
To be honest I really don't see much of tailgating or road rage here in the Chicago burbs. City may be different, but traffic in the city is slow enough such that tailgating will really get you no where. Maybe people here are just nicer in comparison to other states.
Coming from the pre "brake fix" Prius, it is a welcome thing to "lose" braking for a fleeting portion of a second, only to have the brakes work as they should... Before it made your heart jump (if there was a car in front), now, i'd argue it works as good as any brake...
