Prius C in the Big Hills - a Question...

We haven't driven ours on a real mountain yet, but I have every expectation that it would be the same: down to 40mph after the first half-mile of hard climbing.

Fortunately WV is good about putting climbing lanes on the roads that need it. Put the hazards on so faster passing traffic doesn't clip you, and peppermill your way up.

Good luck!

 

Either the mountain is extremely steep +plus loaded down 5 people, or something is wrong with their prius (poor engine maintmainte, old worn out hybrid battery). I driven up steep hills at 80+ mph before, even with the battery low it should still go up the hill at just about any speed you want especially in a normal prius (non c) the engine will just rev high and sound kinda scary. It's fine though, the engine doesn't rev past 5k rpm

 

I have driven up Mont Eagle pass (I-24 between Nashville and Chattanooga Tn) many times in my little 'C', no trouble going up the steepest/longest direction (west bound Chattanooga to Nashville) just last Thanksgiving weekend. I was doing 75-80 mph up the big hill (sucked the fuel mileage though)-could have driven faster but that is usually the fastest I drive period. I also don't have trouble on on-ramps for the Interstate. If these drivers wait until they are already going up the incline before they start accelerating, it may be too late. Unless you have a bad battery pack, the ICE doesn't allow the battery pace to become depleted....got to be a proactive driver, look ahead and determine when/where to start putting foot down on gas pedal-just physics....

 

I haven't driven that stretch of I-24. Looks like a few miles at 4-6%, so yeah... standing on the pedal for 5 minutes straight including a head start at the bottom.

I'm impressed by your claim that it keeps up over several miles of climbing. I would honestly expect it to slack down partway through. Every time I turn around there's another good discovery in these cars...

 

Nope, just give it more gas... I never have had to put the pedal to the floor for the climb (I think the signs state 5% grade-just never paid attention it is 4.5 miles long, elevation of over 1900 ft). I have the 2015 Prius C TWO and have driven this road about a dozen times in my 3-4 time yearly commute from Indiana to Florida.

 

Yup I drive that stretch of I-24 about every week or every other week. All three of my Prii could fly up if I wanted but I'd have to listen to that engine rev.

 

"They" were probably owners of Gen2 Prii, models years 2004-2009. For the folks who had this problem (*), the Gen3 version fixed it.

(*) This definitely wasn't all Gen2 drivers. Numerous Colorado Prius owners here disputed it. But they knew how to drive up steep mountains, at much higher altitudes than exist back East --

 

Let us know how your C performs while in WV.

 

This is my understanding, so It may be wrong.
The transaxle sends 71% of the engine's torque to Motor/Generator2 and the wheels via mechanical gearing. 29% of the torque goes to M/G1 and is spun into electricity. So the harder the engine works, the more electricity it generates. For something like a 6% grade, you may have a higher State Of Charge at the top than the bottom, no matter how long the hill. As it gets steeper, then you may drain the battery, and with a depleted battery all you have is engine. My Gen 2 zipped around the Smokeys no problems. (same engine as a C)

No point in WV is more than 4620 feet above the lowest point, so all hills are shorter than that.

Googling finds this sign coming out of VA in WV.

WV 55 coming West out of Virginia. Its summit is 3295'
(Truckers are worried going down, you are worried going up, but 1.5 miles of 9% may not drain the battery)

"US 33 (between Harrisonburg, VA and Judy Gap, WV.)

There are three summits along this stretch of US 33. The eastern summit is between Rawley Springs, VA and Brandywine, WV. The east side is 4 miles of 8 to 9% grade. The west side is 4½ miles of 9% grade and both sides have continuous sharp curves and hairpin turns. The highway is two lane on both sides.

The middle summit is between Oak Flat and Franklin, WV. The east side of this hill is 2½ miles of 8% with 25 mph curves. The west side is about 3½ miles of much milder grade. It is 4 to 5% over most of its length. There are some sharp curves near the bottom. The road is two lane on both sides of the hill.

The western summit is between Franklin and Judy Gap, WV. It is 5 miles of steady 9% grade on both sides. Both sides are two lane with sharp curves and hairpin turns. Use caution on this road." Mountain Directory for Truckers, RV, and Motorhome Drivers

Again, they are worried going down, where the turns are more important than going up.

U.S. Route 33 in West Virginia - Wikipedia Looks like 3600 is the highest it gets.

Going down these hills is a great time to use B mode. The first time you use it, it is startling how busy the engine sounds, and the harder you brake the busier it gets. This is normal and won't hurt the engine. To me at least it was not intuitive that hard braking would rev the engine in B, but it is working as an air pump, and pumping a lot!

Most googling about grades in WV will be about education.

 

First, that's fascinating about MG1 and MG2 and how those two motor/generators work. Thank you for posting that.

Secondly, I have been on most of those roads in West Virginia, and they're miserable. I do not like driving on those mountain roads, especially the ones that are old (and steeper). Memory can be fickle, but I'd bet some serious dough that the road I was on in January 2017 showed an 11% grade.

I think. LOL.

As to the Gen 2 Prius, are you sure that it had the same engine as the Prius C? I thought that the Prius C was its own little special engine. Just seeking confirmation.

Thanks again for all the info.

 

The Aqua (Prius C) has the electrics & electronics of the 3rd generation coupled to the engine from the 2nd generation. I think it got its own gearing. I know it got its own battery- 10 modules instead of 14.

 

As I mentioned all my googling for 11% Grades found Educational pages, not Highway pages. The best googling was with "Steep Grade"

Here is the Wikipedia on the engine.

Toyota NZ engine - Wikipedia

As mentioned in the article, some improvements were made in 2012. No external belts being the easiest to spot.

 

On Saturday I'm driving from Las Vegas to Kansas City, MO (and back, of course) to spend Christmas and New years with the family. I'll be putting around 3500 miles in the next 2 weeks on the C. I currently have about 900 miles on the odometer. I'll let you guys know how my brand new C behaves in the mountains of Utah and the Colorado Rockies.

Too bad I'm doing this road trip in the winter, otherwise I'd take my Camaro. The LS engine goes through the Rockies like nothing and still get 26 mpg, also engine braking on 3rd or 4th gear is so good, that I barely have to use the brakes during the whole trip.

Let's see how the C behaves... Do you guys recommend using the "B" gear going downhill for a few seconds or up to a minute? This is my very first automatic (CVT) vehicle and I'm still learning on how the C applies engine braking. Thanks.

 

Use B for as long as needed on the downhill, no time limit.

Or at least, no time limit on any hill you'll find in North America.

Posted via the PriusChat mobile app.

 

B is ideal for steep down hills with more than a 600 foot drop. Less than that can go in the HV Battery for better mileage, but more than that will use the friction brakes. Engine braking can help (in the summer it would also keep the brakes cooler, but overheating the brakes or the battery should not be a concern now)

B will still charge the battery, just slower, and use engine braking more than D.

My memory is fuzzy, (I got married in NV one Saturday, then again in MS the next Saturday) but I think B will be more useful on the return trip.

 

That's why I moved to Vegas

Thanks everyone for the input! I can't believe I've been driving manual transmission in rush hour traffic for 14 years (I'm only 30 y/o) and never knew how great is to drive an automatic/CVT. I should have done this a long time ago lol. My daily commute is tolerable now. Loving the C so far (I'm averaging 48 to 51 mpg on rush hour traffic).

 

Just letting everyone know, the C handled perfect in the Rockies with snow... It never hesitated to climb those super steep grades. I drove 3600 miles during this road trip and I got an average of 45 mpg driving 70 to 72 mph on cruise control. I could've gotten better mileage, but the hills in Colorado killed my average. The first 500 miles of the trip (in the flats of Kansas, before I hit the Rockies) I averaged 49 mpg driving 72 mph on cruise control.

 

My old Gen 1 had more-or-less the same 1NZ engine as the c. Gen 1 had a bigger battery though (38 modules; does the c have only 20? I assume the "10" in #13 is blocks, not modules). Gen 1 may have been a heavier car, and the c inherits a lot of later efficiency gains.

I could drive my Gen 1 with no problem up Rockfish Gap on I-64 at 70 mph. But I was also on the same stretch once where I had let my sister drive, who has a different relationship to speed limits than I have, and there were three of us in the car and she was pretty much holding a steady 80. I was watching the ScanGauge and seeing that the battery was chipping in a steady 10 or 20 amps the whole time to make that speed possible, and I saw the charge ticking down through the 50s, then down through the 40s, knowing as soon as it crossed 40% my sis would suddenly find herself driving a 75 hp car up a mountain—but our exit came just before that happened.

That's right, for torque (I've always remembered it as 72% and 28%, but that's not much different).

There's nothing quite so definitive to say about power, on the other hand, because power is torque ✕ rpm and the rpms of MG1 and MG2 are rarely the same. MG2's rpm is always determined by vehicle speed; the engine's rpm has kind of a complicated relationship to its available power and torque, and those two rpms will determine MG1's. For a given vehicle speed, the ECU gets to pick engine rpm and MG1 rpm—not independently, it has to pick a combination that lies on the nomograph, but it gets to pick any such combination where neither one is overrev'd.

It will pick an engine rpm that's efficient for producing the amount of power needed, and MG1's rpm will be determined by that choice, and in the simple case where the battery is happy (at its target 60% SoC and not needed for added power), all of the power produced by the engine will go to the wheels, but over two paths.

(engine output torque ✕ 0.72) ✕ MG2 rpm will be the amount of power taking the mechanical path, and

(engine output torque ✕ 0.28) ✕ MG1 rpm will be the amount of power converted to electricity by MG1 and sent straight over to MG2's coils to be added right back together with the power that took the mechanical path.

That's the simple case where the battery is neither contributing nor being charged ... the tranny is just splitting engine power into two paths and joining them back together at the mechanical output.

Charging the battery is just a matter of running the engine a little bit harder, and diverting to the battery a little bit of the power that's taking the electrical path. Using power from the battery (as for acceleration or uphill) is just a matter of sneaking in some extra power from the battery to whatever is already flowing on the electrical path

The overdrive (or "heretical") mode is not really as weird as it sounds, just a reminder that algebraic signs don't always have to be positive.

So there are some extreme, illustrative cases:

1. If you're driving at near-zero speed (say, just creeping up a steep driveway), the power taking the mechanical path is near zero (the torque is 72% of engine output torque as always, but multiply it by the near-zero MG2 rpm and it's not much power), and nearly all the engine's output power is following the electrical path, turned into volts by MG1 and flowing over to MG2.
2. You can hit combinations of engine and vehicle speed where MG1 is more-or-less stopped, meaning the electrical path is carrying roughly no power, and the mechanical path all of it.
3. In the overdrive mode, 28% of the engine output torque is hitting MG1 as always, but MG1 is turning the other way: its rpm is 'negative' and so is the power on the electrical path. Meanwhile, 72% of the engine output torque is mechanically reaching MG2, which is spinning "too fast": the product of engine torque out ✕ 0.72 ✕ MG2 rpm comes out to more power than the engine is producing—but only by the same amount that's flowing 'backward' on the electrical path, so nobody's getting any free lunch. It's just a brain-teaser way of doing what every overdrive transmission does.

In all of those cases, the split of engine torque between MG1 and MG2 is the same unchanging 28% and 72% (it's determined by the tooth counts of those gears, so it can't change), but the split of engine power between the two paths can run a whole gamut.