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Car Forum / Toyota / Prius / May 2005"Downshifting"
I had the opportunity to "test drive" a Prius the other day and was greatly impressed with the lack of traffic noise inside the closed car. What a tight fitting car! The acceleration is more than satisfactory and the instruments on the dashboard I taught Driver Education and Driver Training for thirty-five years at a school near my home. I always taught my students to "shift down" when they are going down a long hill. Near my home is a freeway off ramp that has the reputation of being the steepest downgrade of all the freeway off ramps in California. I didn't have the opportunity to drive the Prius down that off ramp, and I forgot to ask the sales person. What is the procedure when driving down a long, steep off ramp. It sppears you can't "shift down!" Does the regenerative braking provide extra braking action on the downgrade? Are the brakes on the Prius sufficiently large and cooled to prevent overheating or glazing? Stan > I had the opportunity to "test drive" a Prius the other day and was greatly > impressed with the lack of traffic noise inside the closed car. What a [quoted text clipped - 15 lines] > > Stan * Stan: There is a way to "downshift" -- just put the joystick in "B", which stands for "braking" (I think.) This fires up the Internal Combustion Engine (ICE) and provides engine braking -- actually, it feels very much like downshifting in a regular transmission. In "D-Drive", you get some braking downhill from regeneration, but not sufficient to protect your brakes on a long, steep section. earle * (Happy owner of my '05, now with 6K miles.) >> I had the opportunity to "test drive" a Prius the other day and was >> greatly [quoted text clipped - 37 lines] > * > (Happy owner of my '05, now with 6K miles.) Beyond my direct experience, but... others on the Yahoo Prius group reported checking their brakes after a long steep downhill and found them still cold. Regenerative braking should be enough for several miles of repeated braking or prolonged deceleration. You can tell when the battery is too full to absorb more by checking the battery icon on the "energy" display. Our 2002 fills after about 2000 feet of descent - I don't know about the second generation models. Once the battery displays full, use of "B" will reduce wear on the brakes. Before that it just wastes energy that could be partially reclaimed. I agree this is very counter-intuitive to us geezers. I downshift our Volvo dozens of times a day to reduce brake wear in this hilly town and have to remind myself the brake is the best way to slow the Prius except on very long low speed descents. (At freeway speed the aerodynamic drag is enough to keep the battery from filling on any decline I've encountered on the West Coast.) Mike > I didn't have the opportunity to drive the Prius down that off ramp, and I > forgot to ask the sales person. What is the procedure when driving down a > long, steep off ramp. It sppears you can't "shift down!" Does the > regenerative braking provide extra braking action on the downgrade? Are the > brakes on the Prius sufficiently large and cooled to prevent overheating or > glazing? When you find yourself riding the brakes when going downhill, put it in "B". This increases engine braking (the engine spins without fuel or spark, using kinetic energy to pump air; "jake brakes" without the noise). Don't forget to put it back in "D" at the bottom of the hill or fuel economy will suffer. > When you find yourself riding the brakes when going downhill, put it in > "B". This increases engine braking (the engine spins without fuel or > spark, using kinetic energy to pump air; "jake brakes" without the > noise). Don't forget to put it back in "D" at the bottom of the hill or > fuel economy will suffer. I was under the impression that constant light to moderate pressure on the Prius brake pedal governed the battery regenerative charging rate and that "riding" the brakes going downhill improved fuel economy. If my understanding is correct, only steady, heavy pressure would engage the mechanical brakes causing them to overheat. > > When you find yourself riding the brakes when going downhill, put it in > > "B". This increases engine braking (the engine spins without fuel or [quoted text clipped - 6 lines] > understanding is correct, only steady, heavy pressure would engage the > mechanical brakes causing them to overheat. True, but after a year of ownership I can't tell when the mechanical brakes have engaged. And some prefer to use "B" rather than wear down the brake pads. Certainly one should use "B" when going down, say, Mount Hamilton near San Francisco. >> > When you find yourself riding the brakes when going downhill, put it in >> > "B". This increases engine braking (the engine spins without fuel or [quoted text clipped - 14 lines] > the brake pads. Certainly one should use "B" when going down, say, > Mount Hamilton near San Francisco. Having bicycled over Mt. Hamilton a few times (when I was young and studly) I think the San Jose side is beyond limit of the battery capacity - IIRC it is about a 4000 ft descent - and using "B" would be just right. The Livermore side should be just fine with regenerative braking. The five mile descent would certainly charge the battery, though! (My worst bicycle accident was on Mt. Hamilton. I was using tubular tires and forgot I had changed the front tire on the way up - it rolled off the rim in one of the turns above the switchbacks at over 30 mph. When I recovered my senses I had almost exactly half a shirt left - the front, left sleeve and collar. My body was road-rashed to match.) Mike |
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