Extended driving on an incline

I don't understand the question. Is this your experience? Or are you asking how the Prius works?

The car is pretty smart and does a great job regulating the battery and a great job going up hills. I travel along a very hilly commute (Rt. 2 west of Boston) and still manage in the 50s for mileage through this winter (with the hopes of higher once it finally warms up).

 

9% grade for 8 miles, sea level to 4570' no problem on cruise at 65 miles per hour.

 

To put it closer to home, I drove the Grapevine with my '05 (that's I-5 for the unitiated between L.A. and Bakersfield -- a long time graveyard for brakes and radiators). It basically did fine in terms of speed -- so long as no-one cut me off and I had to regain speed. The mpg on an extended uphill climb was comparatively terrible -- that is, compared to other driving in the Prius. I suspect that I made up the mpg by driving that same route back and watching the display show 99.9 mpg for extended periods of time.

Ted


Ok, I know how sensitive people get when there is an appearance of crticism, but I think this is a valid question.

Has anyone driven the prius over an extended period of time on an incline? At some point the batteries lose all it's juice and the gasoline engine is the only thing powering the car. So the 140+ hp car becomes a 76 hp car. Does is still have enough power to make it comfortably up?

I'm just thinking about the philosophy difference between the civic hybrid and the prius. Civic has lower hp overall but its gasoline is 93 hp.

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I wouldn't expect it to be a problem though I have not done mountain driving. Keep in mind that on the way down, you'll get great mileage as well as a terrific charge of the battery. FYI - You'll probably top off the battery and end up with engine braking instead.

Good luck.

 

Should be just fine. With most cars, I'd be more concerned about the brakes on the downhill. CA has some pretty long steep downhills that require a lot of braking. In our old Accord, I can remember the brakes getting overheated on the incline going down to Santa Cruz. This is where I would expect the Prius, with regenerative braking (and the infamous B mode) to really shine. Can someone confirm this?

 

Towne Pass in Death Valley tops out at 13%, which is quite steep for a paved road. I have driven over it and did need to slow down near the top, as would most other vehicles I suppose.

Interesting to do the same climb with the cruise control, because then when the HV battery charge drops to some preset level, CC cuts out. But press the accel pedal and the power is available.

 

Our '06 does nicely in the Santa Cruz mountains. If i'm in traffic, i'll use B, otherwise its just a nice, fast drive on the way down (either side).

 

Us B mode all the time on long steep hills hardly ever touch the brakes. Lots of mountain passes here in B.C. and have never had a problem going up or down.

 

I wouldn't call it extended driving on an incline, but I regularly drive up grades in my new 2006. Of the 460 miles on the odometer, nearly 150 have been up an incline. My commute includes the 7% side of the Sepulveda pass in the morning, and the 10% side in the late afternoon. This is nealy a 1200 foot change in elevation going each way.

First of all, when it's traveling at the rate of traffic, the car doesn't struggle at all. The ICE runs at high RPM, but it moves easily with the flow of traffic. But, accelerating from a stop, or even a near stop on the grade is more of a struggle than it was in my last car (a Camry).

The battery assistance on an incline is far less dramatic than advertized... in fact the charge indicator vascilates through the entire trip, which would seem to reflect that the battery is only infrequently engaged.

On the incline the car averages 25 MPG at 65 MPH if the flow of traffic is steady. When it has to accelerate and decelerate that average can go as low as 14 MPG over the three miles of slope. I've found recently that the cruise control is actually fractionally less efficient on this stretch than conventional control over the accelerator.

Coming down the far side of the pass, though, I average above 99 MPG and generate a full load of charge (I'm not sure whether a SOC with all bars full is particularly good for the batteries, but my car spends a good third of the time in this state). When I return to surface streets the car doesn't want to come out of stealth mode. In fact, it doesn't want to stop. When I come to stoplights, for the first few miles after leaving the freeway, the car bucks slightly engaging the elecrtic motor and disengaging it to kill some of the excess charge.

By the end of the day, with two trips through the pass I still average above 50 MPG, largely due to the excessive charge that the trip downhill genrerates. The car is more efficient going South, up the 10% and down the 7% grade, because it gets better efficiency going up the more extreme grade and better distributes the potential energy over a longer stretch of roadway. On the way in to work in the morning I'm lucky if I get it over 40 MPG on cooler mornings.

Mind you, this is a brand new car, not broken in... but I do try to drive it carefully.

 

Ok.. excuse my lack of knowledge...

How do you know the '%' grade of a hill? I've never seen it on any road sign, etc.

 

rarely if ever published. some mountain roads mention it on grade warning signs.

 

Just for fun I did a search for the Sepulveda Pass. I found a great picture.

 

With some major roadways its a matter of easily accessible public record:

Like Fargo Street, or Eldred Street in Los Angeles...

And with others you calculate it. Rise over run. Altitude in feet, divided by the distance traveled in feet.

 

Coming back from picking up my Prius in Mesa AZ I drove through the mountains near Payson AZ. Going up one incline with a passing lane I saw a Hay truck nearing the top. I wanted to get by him before losing the passing lane. I topped the hill and saw 95 mph on the speedometer. I did not have it floored and it felt as if I still had more power. I will be driving to Sandia Peak soon. 5000 ft climb in 14 miles. I will report back after that.

 

The short answer is: don't try to pass anybody. Constant speed will be OK.

If you are curious about the car's limits, this math will give a reasonable approximation:

The ICE maxes out at 55 kW,
Prius weight 1400 Kg (with one passenger)
Flat energy use at 30 - 50 mph is about 10 kW, leaving 45 kW for climbing
1 mph = ~ .45 meter/second, so climbing/second is incline% * speed(mph) * .45 in meters/sec
Work of climbing is m*g*Height, power is m*g*Height/second

Example: Can you stay at 33 mph on a 10% incline :
You are climbing ~ 1.5 meters/second, so power required is
1400 Kg * 1.5 meter/sec * 9.8 meters/sec^2 ~ 21000 watts, or 21 kW.
More than enough.

50% faster, you say ? 32 kW, at 50 mph.

As an aside, a short trip through Wikipedia trending the size of engines will show you that 75 hp was a quite respectable engine not so long ago. The roads have not changed much .. only the marketing hype.

 

Sandia is a snap. Although having the HV fill up, and then *waste* the rest of the energy going down is painful.

 

Where are the Coloradans?

centel, where will your mountain driving be?

I've been on Prius boards since '01, as have a few others here. The ONLY reported cases I remember reading about where the battery was exhausted and could not contribute to a climb was approaching the Eisenhower Tunnel on I-70. For the last couple of miles the power did indeed drop significantly (but not to a crawl---more like 30-40 MPH).

That was on Gen 1's. The Gen 2 significantly boosted the battery power. I don't remember reading about any such instances since the '04s came out. But tripp and the other Coloradans can tell us.

Frank's experience in BC is instructive. So is that of anyone who climbs the Grapevine, or the run to Cajon Pass on I-15 up to Victorville, CA.

I've taken my Gen IIs from Sacramento up US 50 to Tahoe and I-80 to Reno. Never came close to depleting the battery that I know of---but those routes offer a few plateaus along the way where the battery can recover a little. The most punishing climb I can think of, with no respite for the battery, is that one on I-70. (The road up to Mt. Evans would be another---anyone do that one?)