I am heading out on a 6600 mile trip from GA to Jackson Hole and back on Wednesday. Any special advice for driving in the mountains out west.

I just had the 60000 mile service done and new tires, which I am going to be upping the psi on tomorrow.

 

Good luck on the trip!

Just a couple of tips:

• climb at 55 miles per hour if you can for the most efficient fuel-to-altitude climb ... I use the truck climbing lane and pace to their speeds
• use "B" as much as possible on the downgrades to minimize stressing your traction batteries
• cruise at ~65 miles per hour as much as you are able, avoid over 70 miles per hour

So what year Prius do you have?

Do me a favor and keep a rough log of your driving segments:

1. miles and time per segment
2. MPG per segment (reset MPG for each)
3. weather (aka., temp, winds)
4. route information

This will help us map your Prius performance on the miles per hour vs MPG charts.

Watch out for thunderstorms in the midwest that can often have hail.

Thanks,
Bob Wilson

 

Use "B" to avoid stressing your hybrid batteries....??

I think the hybrid battery charge/discharge control system is quite well attuned to task of preventing "over-stressing" or even undue "stressing" of the hybrid battery. I sincerely doubt that using engine compression braking ('B") will do anything other than helping to prevent brake fade on a longish downhill drive, just as the owners manual states.

My suggestion would be, for a longish downhill drive, to leave the system in normal mode until/unless the hybrid battery is fully (re)charged. Once that point is reached then regenerative braking can/will no longer be used to assist frictional braking and so it is best to switch to "B" to use engine compression braking to help alleviate the possibility of brake fade.

 

Hi,

This is from a study I did about two months ago:

What I did was 'force charge' my battery in preparation for a battery capacity test. But during the charge, I recorded the maximum and minimum battery module temperatures:

• weakest had 9C increase
• strongest had 7C increase

What we find is charging NiMH batteries is exothermic, it releases heat, making the batteries warmer. This is in addition to the ohmic heating from the charging current. So the batteries can quickly get pretty warm, in fact, hot enough to turn on the fan. Yes, the discharge is endothermic but this appears to be balanced by the ohmic heating from the discharging current.

What appears to happen is driving through mountains, ~1,000 ft. changes, during the descents in "D", the batteries get not only a charge but a lot of heat. During the subsequent climbs, the temperature stays the same until the next downgrade, heating the batteries again.

I verified this on a 925 ft. hill near Huntsville and was able to verify descending in "B" gave half of the heating load to the batteries as compared to descending in "D". For mountains of 1,000 ft or more, there is too much energy to store in the batteries anyway on the descent.

Using "B" is easier on the batteries by minimizing the amount of extra heat. For mountains of 1,000 ft. or more, the batteries can not store all of the energy from the downgrade anyway. I prefer to minimize heating my batteries.

Bob Wilson

ps. Here is the complete picture:

 

"climb at 55 miles per hour if you can" Planning on this, but did not know if I could step out and pass a truck if I needed to. My wife gets a little scared around big trucks.

"use "B" as much as possible on the downgrades" Had not though about this, but will take your suggestion

"cruise at ~65 miles per hour " funny you say this. In my informal test, I have found that I get better mileage at 72 than any where in the 60's. I know what the math and science say, but I swear that I can watch the instant mpg climb when I cruise at 72 -74mph. I will do several test over the 6000 plus mile trip and see what I get.

So what year Prius do you have? 2005

Do me a favor and keep a rough log of your driving segments:

1. miles and time per segment I do this in my head at each fill up, but I will put it on paper so I can update this site.
2. MPG per segment (reset MPG for each) MFD calculation or hand calculation?
3. weather (aka., temp, winds) This should not be a problem, should it. Just kidding. I was going to need new tires in about 200 miles and went ahead and spent the $500 before the trip just for this reason
4. route information I will post my Google map after the trip. Don't want the bad guys to know my every move while I am away.

This will help us map your Prius performance on the miles per hour vs MPG charts.

Watch out for thunderstorms in the midwest that can often have hail.

Thanks,
Bob Wilson

Thank you for the info. If I get an internet connection along the way, I will update as I can.

 

You should have no trouble passing trucks. Pearl continues to surprise the drivers of SUVs and the like, as they pull out to pass me at the bottom of a two lane up long hill. They are astonished as I pull away from them.

Bob is correct in that heat is the enemy with batteries. Nice charts Bob. Probably good advice on using "B" right from the start of the downhill mountain pass portion. I'm not sure it would make a measurable difference in battery life, but it wouldn't hurt.

Do expect to hear the engine roar (quietly) . I've seen Pearl hit 5000 RPM quite a bit, both uphill and down. That's the "maximum recommended engine operation speed". The car will not exceed it, appearantly.

I use a Scanguage II to monitor:
Engine RPM -------------- 12 V Battery voltage
fuel consumption (L/Hr) ----- Coolant temp.

Bob uses a higher tech gadget.

 

Nobody has all the answers so it helps to get every extra data point for every speed. The more the merrier.

GOOD LUCK!
Bob Wilson

ps. This is what I have so far:

 

"Using "B" is easier on the batteries by minimizing the amount of extra heat."

What is your definition of "extra heat"....???

Or are you just "second guessing" the Toyota design engineers...?? Assuming they didn't do their "sums" correctly and therefore the batteries are subject to overheating in certain instances.

I would imagine the overall system is designed not to exceed the charge rate and therefore NOT to generate extra heat, or at least not to generate a level of heat that would inordinantly shorten the battery life.

Regenerative braking is your only source of FREE fuel, so I would allow the system to charge the hybrid battery to the highest level it will/might and only then switch to "b" to reduce the potential for or prevent brake fade.

 

Hmmm, I know that when I was travelling to/from Montana a few years ago, I never tried to go faster than 45 mph while climbing the steep parts. That was where my car seemed to be comfortable in the mountains on steep grades.. go figure

 

An avoidable battery increase in temperature that does not improve vehicle efficiency. It comes directly from field observations. For example:


Of course folks may agree to disagree on whether battery temperature is important. I prefer to avoid it and primarily use the battery to optimize ICE performance.

Bob Wilson