Over-revving in "B"
#1
Over-revving in "B"
Several times I've been going downhill in "B" and the engine suddenly revs up to a very high rpm -- loud enough to hear.
Most of the time, shifting into "D" takes care of it, but once I had to shift to "N" to slow it down.
This over-revving only happens maybe 1 in 10 times I'm going down the same hill.
Any idea as to what's going on?
Most of the time, shifting into "D" takes care of it, but once I had to shift to "N" to slow it down.
This over-revving only happens maybe 1 in 10 times I'm going down the same hill.
Any idea as to what's going on?
#2
Re: Over-revving in "B"
Engine braking. Putting the vehicle in "B" causes a higher rpm's, which is what slows you down via the engine. Think of it like shifting into a lower gear, the engine will get louder because it is working harder. I rarely use "B" because it puts more wear on the engine and I'd rather wear out my brakes than my engine, brakes are cheaper to replace.
#3
Re: Over-revving in "B"
Originally Posted by PriusNut
Several times I've been going downhill in "B" and the engine suddenly revs up to a very high rpm -- loud enough to hear.
Most of the time, shifting into "D" takes care of it, but once I had to shift to "N" to slow it down.
This over-revving only happens maybe 1 in 10 times I'm going down the same hill.
Any idea as to what's going on?
Most of the time, shifting into "D" takes care of it, but once I had to shift to "N" to slow it down.
This over-revving only happens maybe 1 in 10 times I'm going down the same hill.
Any idea as to what's going on?
It would also help to know your entry speed to the grade and what typical speed ranges you are seeing. The reason is the amount of 'braking force' required is a function of your speed. The faster you go down a hill, the greater the retardation force needed to control the speed.
There is no reason to worry about the ICE over-speeding. It is computer controlled and the controller will prevent any problems. It may seem like "sound and fury" but it signifies 'nothing' to worry about.
Given your report that it happens "1 in 10 times," I'll speculate that it is a function of your traction battery "State of Charge." It may be the higher revs are associated with the battery becoming fully charged and unable to absorb more energy. In that case, the ICE has to work, effectively trying to 'go into reverse' to slow you down. But absent other observations such as MFD display arrows or MPG changes or auxillary instrumentation, this is pure speculation.
I have tried going down some local hills in my NHW11, 03 Prius, at a pretty good clip, entry 70 mph, using "B" and so far, I don't remember hearing the engine race. Using "B" works and my NHW11 Prius reaches a near steady-state descent at 65 mph. If I enter too slow, the vehicle slows to less than 30 mph while descending. If I enter too fast, it will try to run away but a light application of the brake brings it back to a stable speed.
Bob Wilson
#4
Re: Over-revving in "B"
The next time it happens, I'll check the battery state.
http://www.topozone.com/map.asp?lat=41.07212&lon=-74.24627&size=l&symshow=n&u=4&datum=nad27&layer=DR G
The road is called Skyline Drive and seems to drop 300 feet in about a mile.
Thanks
http://www.topozone.com/map.asp?lat=41.07212&lon=-74.24627&size=l&symshow=n&u=4&datum=nad27&layer=DR G
The road is called Skyline Drive and seems to drop 300 feet in about a mile.
Thanks
#5
Re: Over-revving in "B"
Originally Posted by PriusNut
The next time it happens, I'll check the battery state.
http://www.topozone.com/map.asp?lat=41.07212&lon=-74.24627&size=l&symshow=n&u=4&datum=nad27&layer=DR G
The road is called Skyline Drive and seems to drop 300 feet in about a mile.
Thanks
http://www.topozone.com/map.asp?lat=41.07212&lon=-74.24627&size=l&symshow=n&u=4&datum=nad27&layer=DR G
The road is called Skyline Drive and seems to drop 300 feet in about a mile.
Thanks
My hill is a little taller, ~480 ft., and a little longer:
http://hiwaay.net/~bzwilson/prius/pr...r_Brindley.jpg
The "Heart of Dixie Highway" is posted at 65 mph and "B" handles that very nicely.
Bob Wilson
#7
Re: Over-revving in "B"
You don't have to brake when the engine rev's up! Bob explained the high revolutions are perfectly normal. While in "B" mode just let the Prius do its own thing unless "B" is not slowing enough.
Wayne
Wayne
#8
Re: Over-revving in "B"
Grades steeper than 6% are rare on paved public roads, and that's about what you are looking at. The use of Prius B is apparently somewhat controversial. No doubt that it can be overdone, but I wouldn't say that engine wear is a major factor. It makes more noise, there are some unusual things going on inside, but nothing harmful to the engine.
I have driven 2001 Prius almost 100k miles, and I use B on all long descents. Whether 300 feet qualifies as 'long' might be a matter of mood. One thing that is different about the newer model Prius is that you are not allowed to use cruise control in 'B gear', but that may be unrelated to your observations.
DAS
I have driven 2001 Prius almost 100k miles, and I use B on all long descents. Whether 300 feet qualifies as 'long' might be a matter of mood. One thing that is different about the newer model Prius is that you are not allowed to use cruise control in 'B gear', but that may be unrelated to your observations.
DAS
#9
Re: Over-revving in "B"
From a 'human engineering' stand point, I would prefer "B" require a 'release' before engage. The problem is when you leave "P", you hold down the button and have to stop at "P". If you just ride the handle to the stop and let up, you' re in "B" and take a mileage hit. I'm convenced this is what happened to my wife when we rented a Prius in 2001.
Bob Wilson
Bob Wilson
#10
Re: Over-revving in "B"
I watched the Energy screen on the way down my 300 foot hill and, sure enough, as soon as all the battery lines appeared, the engine revved up.
I'm having a hard time believing that the high revs are OK for the engine; it just doesn't sound right.
I want to figure out how to get the battery as low as possible on the way up the hill. Any suggestions?
I'm having a hard time believing that the high revs are OK for the engine; it just doesn't sound right.
I want to figure out how to get the battery as low as possible on the way up the hill. Any suggestions?