So, along my commute I have a 3 mile climb in each direction and it gets pretty steep, I was wondering what way to approach hills and/or mountains, or what ways do you use? Basically what I'm asking is do you accelerate up the hill/mountain as quickly as possible burning more gas for less time or do you accelerate slowly burning less gas for more time? I'm sure that you could perform some sort of mathematical equation for this, but I'm no mathematician, so I'll leave this to someone who wishes to figure it out. Any tips, tricks or otherwise?

 

I'm no expert on this, but because of the way HSD works, your battery will recharge on the way down. So, it's likely most efficient to go ahead and use that battery on the way up and not force the engine to charge it as you're going. I would use significant power going up, using both the engine and motor outputs. If your battery drains, who cares? At least you won't throw out the extra energy once the battery fills up going down.

 

I have lots of these challenges for my daily drive in my HCH.

First, I make sure that I'm going a pretty good speed as the hill begins. I might take 2-3 miles or more to gradually increase my speed to the base.
Basically speaking, I let her slow down on the way up.
Before I begin the hill I'll decide the minimum speed required at the top. Often times the current traffic condition plays a big part in that decision.

You'll also notice that the hill(s) are not linear to the top: they usually have level or more level areas on the way up. These areas do not require as much fuel as the hill itself and you can save a little more on these areas by backing off a bit.

Since this is your daily commute you know the road very well and can plan far in advance.

In my commute I have a set of staircased very long, steep hills. These are paticularly problematic because there is a light that almost always requires a stop before the hills begin.
The staircase begins just on the other side of the light so there is no chance for a long, gradual period of momentum building.
These are in the first quarter of my 46 mile commute and still have ~20 miles to go before getting any real downhill relief.

I'll begin with a fair amount of accelleration from the light * until I reach the base of the hill, then I'll conserve what I've just burned and keep momentum by backing off just enough to maintain speed up the hill.
At this point I'm still well below my desired speed so on the following more level area I'll increase speed again and go back to the astrisk * (above).
I'll increase speed on the level areas until the desired speed is achieved.

I'll also be certain that the AC is not running during these taxing events.

This technique has worked well in both my HCH and Grand Caravan and surely would at least give it a try in your Prius and see what it does.

 

Yeah, on the way down (which is just as long as the way up of course) I have plenty of time to recharge the battery, basically the speed limit is 65 and I can coast down starting at 60 and get up all the way to 75 or so, but it has some dangerous curves that people like to slow down for, so they sometimes get in the way. I was just wondering how the rest of the folks here tackled them. I guess getting up faster is better. I did a not so scientific test of the hill and faster seemed to get me better mileage, but I need more research before I come to a decisive conclusion.

 

Remember that different hybrid systems are good for different things. Hybrid Synergy Drive will give different results than Integrated Motor Assist in the same conditions.

 

You really need to get to know your route and your car to determine the "best" way to tackle hills. There are too many variables that could make any single method the best on a givin day. Certain techniques are always good but as conditions change you must change your method.

What changes? Same car, same hill right? Well not really. The wind and the charge in your pack can make a big difference in how you get over a hill. Traffic, stop lights and rain can affect the results as well. My HCH acts differently depending on how warm the engine is as well.

Examples:

1) I've got 2 similar hills to climb at the beginning of my commute. In the cold the car has not warmed up yet so I can get up the first hill in top gear with no assist if I take a running start at it, if the wind is not too strong in my face. The car is usually warmed up by the second hill and for some reason assist is more aggressive when the car is warmer. While the first hill is longer and steeper I have more trouble climbing the second hill. If the wind is blowing a downshift is required about half way up each hill to make it over.

2) I usually take most downhills with the engine off. If the hill is not steep enough to maintain speed ICE off with current wind situation the ICE must be kept on to add impulse to the system. If the hill is so steep that your speed increases over the limit the ICE must be on to use regen to slow the car down. Also if the pack is low I'll leave the car on to get some regen back in the packs.

3) Cresting hills is traffic dependant for me. Going to work there is more traffic so I crest hills faster so as not to slow anybody up. Coming home at night there is no traffic so I crest hills with just enough speed to make it over the top and the engine off.

4) If the pack is fully charged you might bang up a hill in top gear using a little assist to got over. If the pack is drained you might need to downshift to get upthe hill without assist. A downshift might also be required if it is raining, windy or if for some reason (traffic, stop light) you could not take a good running start at the hill.

Really long hills will drain a pack completely. There is only one such hill in my area and it caught me by surprize because the HCH can take all the other hillls in top gear no problem. I've only been over that hill once and it was quite a struggle once that pack was dead.

 

I live on top of a hill with a bit under two miles of pretty steep grades to get between home and to the freeway. Coming home, I have to climb to the top of the hill, then go back down a rather long cul de sac to the house, so each trip is up and down. What I usually do is get up to speed on the flat part at the base, in some cases requiring somewhat of a "jackrabbit" start because there is a stop light, a short flat part, then a climb, but I've actually averaged a bit better doing this than trying to accelerate while climbing, steadily. Unfortunately, the trip up and down has lots of stop signs, and lots of very sharp turns. This forces me both to drive much slower than would be good for fuel economy, in addition to requiring myself to stop and start often. Going down, I can never maintain momentum for very long either, thanks to the stopsigns.

What I usually do going up is get up to speed, a bit faster than the speed limit, then as I go up, lose speed on the steep parts, and regain it a bit on the flatter parts. I also allow myself to coast up to the stops in such a way I don't even need to use the brakes at all. I've also gotten good at taking each turn as wide and as fast as safely possible, so as to conserve momentum. Finally, I feather the throttle so that the FE is as high as possible, while still delivering "assist." By the time I crest the hill, my battery is close to empty, and I can recharge it a fair amount coasting back to the house.

Going down, I do the following: Shift the car into "S" to control speed (I drive a CVT, not a manual), while still tapping on the brakes just enough so that it kicks in all the regen braking without 'riding' the regular brakes. In addition, I run the air-conditional all-out while going downhill, It actually helps me brake, and it gets the coils nice and cool before I begin my normal drive. Later, when I get on the freeway, I can turn the thermostat to a higher temperature, or switch to fan only.

Since I optimized my semi-daily hill climb routine, I've found my FE has been helped very, very dramatically. For a straight "up and down" trip among the more forgiving routes, I average about 36mpg. That's better than most typical cars average on the whole, and only slightly worse than some lifetime averages for the HCH itself. I average just under 52 overall, even with a lot of short trips (I'm thinking it's time to pump up the tires, they're starting to get a bit too "cushy" for my tastes...)