Best way to climb a steep hill?

I live at the top of the hill and there is no hope. No matter what I've done it's bad gas mileage.

 

By trying to stay out of the ICE zone you were forcing an inefficiency. By draining the battery you'll force the car to recharge it in addition to moving the car more directly.

Think of the energy that you take from the battery as more expensive since the engine had to do that work anyhow and there are losses both in charging and discharging it.

As you found out, you're best off taking as good a running start as you can and use the ICE up front.

 

The method that works best for me is to gain enough speed on the long level approach to minimize power required on the hill.
In either case, especially the 3 hill set if there are turns involved aka snaking that will consume more gas.
Content yourself with the fact that coming off the hill will gain some of the mpg's back if you don't have turns involved (use the long straight hill)

 

Honestly, just give it the gas early and get up the hill and keep your speed up. The sooner you are done with the hill, the less gas you use. Your car may sound unhappy and your fuel economy may suffer, but that's just life taking you up hill.

 

I have an exaggerated version of what you describe on my daily commute at interstate speeds. There is about 8 miles of either straight uphill/downhill over a 600ft elevation change, or the other option is about 4 undulations covering approximately the same distance (slightly longer).

I find per the MFD MPG that it is more efficient to come downhill via the undulating route and return uphill via the direct route.

I would expect a lower speed trip to be similar, but I don't have enough evidence since battery use and SOC seems to play a more transient role there. I'd think that all Gen's of Prii would be similar in this behavior on elevation changes.

 

This assessment of battery energy is pretty commonly stated, but is, in most cases, incorrect. If the battery is being charged by the regeneration systems, the energy is essentially free. Even when the engine is doing the charging, it is constantly adjusting the rate to use "excess" energy as the engine runs. While you should probably assign some gasoline cost to this charging mode, the battery contains the cheapest energy in the car. If you are driving in stop-and-go traffic, you should use the battery energy as it will be regenerated as you drive. This does not mean use the EV button, but use the battery to extend your glide (EV on the system indicator) while the engine is off. Driving with six bars or more on the battery indicator is wasting the opportunity to reclaim energy and that will decrease your mileage.

 

I agree with drysider's comment that "Even when the engine is doing the charging, it is constantly adjusting the rate to use "excess" energy as the engine runs." An ICE develops its highest efficiency (lowest Specific Fuel Consumption) when the throttle is nearly wide open. Therefore, I suspect, but can't prove, that the ICE sometimes operates at a higher power output and throttle opening than necessary to propel the car. The total work output from the ICE is therefore obtained at higher efficiency (less fuel usage) and the excess energy is stored in the battery, thereby increasing the fuel mileage. I think the best fuel economy is obtained by driving with the ICE off as much as possible. There is a close relationship between EV% and fuel mileage.

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Hardly free. It's a percentage of the kinetic energy reclaimed while slowing. But that kinetic energy came from burning gas. And to the extent that you drain the battery below the "target" charge you'll end up paying it back with interest.

Unless you're assuming that the hill climb will be followed by a descent that maxes out the battery capacity there's no reason to keep the power setting lower than the trigger for the ICE.

 

what i like to do, and i don't recommend this for everyone, but for those with the wherewithall; slow down as you approach hills, to the point where you're comfortable that your not going to get rear eneded. best to stay in the right lane. when you reach the precipus, floor it in power mode. this will recharge your battery as well as get you to the apex in short order. not only do you use the least amount of petrol possible, but you'll have enough kinetic energy to carry you through the next valley and hill. i use this method all the time in the mountainous areas of massachusetts with excellent results. all the best!

 

oops, i see you have a prius c, sorry, disregard everything i just said.

 

The regenerated energy is, as I stated, essentially free. Lacking a good source of thiotimoline, you cannot assign energy costs to an event that has not yet happened, which may not happen, and if it does, it may not happen very much. The gas costs are sunk into getting the vehicle from point A to point B. Anything that happens after the combustion in the cylinder is not causally connected to the burning of the gasoline.

 

But if I hold off using it immediately I can save it for later and avoid the extra gasoline that will be needed to replenish.

I agree that for low speed low load driving EV makes perfect sense. For starting a significant ascent I can't see it.

 

Cmon. The energy required to asend a hill is determined by weight, change in elevation and how quickly its done. Any extra engine power is a result of more gas burned. The trick is minimizing the energy expended. Turns are verboten. The best minimized energy is to gain speed when it's least energy expended and let momentum carry you as far as possible.There's a minimum somewhere in that process and its specific to every vehicle, hill, and weather conditions.

 

Here is my trick to over take a steep hill:
1. Estimate the lowest speed I want on the hill, let say 55 mph on the highway. I speed up as fast as I can before the hill (make sure not put yourself in danger or get a ticket ~70-75 mph).
2. Press more down on gas pedal when come to the hill, but I never floor my car. I just think it is bad for the car in general, so I never floor my car. Hold gas pedal at same level to pass steep mountain. Of course, the speed will drop slowly to ~55 mph when I am at top.

The key is to use momentum to pass the mountain. In general, the slower you go, the better gas milage you get. But for the C on steep hill, the rate is much higher compare to other cars. So instead of 55mph is the lowest, you can drop to lower mph to get better mpg. I just hate to go slower than 55mph on highway, so I tried to stay over 55 mph even on really big hill.

 

Many on this forum are down on cruise control when it comes to hills.

Their point (and it's a valid one) is that in varying terrain the cruise control can't anticipate climbs and descents and thus is always lagging and working to cross purposes.

Here's where it's a good tool: for long (multiple mile) grades. The running start with decaying speed concept only takes you so far. As you're starting a prolonged, relatively steady climb you should establish in your mind the minimum speed you want to use for the climb. Manage your approach and initial climb however you want but plan on engaging the cruise control as you reach your targeted minimum climbing speed. This will prevent you accidentally dropping below that speed and then facing the choice of living with the lower speed or wringing that extra power from the power train to catch up again.

I'm only recommending this for when the grade is not constantly changing.

I have occasion to drive some pretty level stretch of road as well and make it a point to use cruise control there if traffic permits.

 

Ok so what I do is firstly try and avoid the hill especially when I can get 70mph+ to drive through town. If I must climb the hill. I take the car out of eco mode (just remember to put it back on after you've reached the top) I accelerate to just before the power section. If I need to I can pull over, but I have noticed once the car is out of eco mode it's a bit more powerful. And the kicker is, once at the top of the hill, I can engage the braking gear and enjoy the ride.

 

hit the hill at full speed and coast up and down

 

A lot of this comes down to engine efficiency, which is why there is no one right answer for all hills/speeds.



Comparing these graphs, the Gen2 hits peak efficiency at about 28kW, while the Gen3 hits peak at about 20kW. To put that in perspective, a Prius needs somewhere in the vicinity of 14kW to maintain 60mph on a flat. 40mph is only about 6.5kW. This is in essence why pulse and glide works. Even though accelerating and decelerating takes a bit more total work, at lower speeds in particular overall efficiency is raised by pulsing the engine between max efficiency and off compared to just running it at a constant speed.

The same can be true of hills. Even though climbing and falling takes a bit more total work, if it allows you to operate the engine at significantly higher efficiency your total overall efficiency can be better on hills than on the flat (at least flat constant speed, and particularly lower speeds).

Rather than a specific strategy of accelerating/constant speed/decelerating on hills I typically shoot for the ICE rpms that equate to peak efficiency when climbing. I don't have a scangauge, so I've just learned over the years what the engine should sound like If max rpm is 5000, 2500 is an octave below that Once at that rpm sweet spot, I just let the vehicle speed do what it will within reasonable bounds of course. At lower speeds / more gentle hills I would end up accelerating, at higher speeds / steeper hills I'll end up decelerating. If I think a hill will be an accelerating hill, gliding to hit it at a lower speed will let me keep my speed reasonable longer on the way up. If I think a hill will require losing speed, taking a run at it (again at peak efficiency rpm) will similarly help stay at a reasonable speed on the hill longer before having to deviate from peak efficiency. Reasonable speed is based both on safety and on knowing that increasing speed too much will degrade efficiency due to wind resistance.

That sounds like a lot of work, but it just kind of becomes second nature after a while. In general I've found that my overall mileage improves as a result of having hills to play with.

Rob