Orange4boy's Rescue and Revival of a 2003 Prius

[Daox]

I'm pretty sure all the Prius block heaters are the same. Its the same one they use in the the Corolla and Matrix too. I think I got mine online for ~$35 US. I got it from www.1sttoyotaparts.com. They don't have it listed on their site so you have to call em.

[MetroMPG]

Marcus, care to summarize cost to date for resurrecting the car?

[orange4boy]

Just took it's first highway run from Bowen to Mission, with a stop at friends in East Van so actually 30%city/70%hwy. Got 4.4 L/100km or 53.46 mpg according the the MFD (usually optimistic) MG1 was almost always warmer than MG2. Needless to say, I'm thrilled.

Love the car. Fairly quiet, smooth and fun. Lot's more tailgaters that when I'm in the van but I was probably driving slower.

Costs so far off the top of my head not including taxes:

Slightly scuffed 2003 Prius 168,000km. $1500
Slightly less scuffed 2001 Transaxle. $1000
Shipping. $90
Parts, oil, ~ $120
25 hours hard labour. Well, sort of free. I'm my own slave.
Total $2710
2001 scuffless Prius on dealer lot with same mileage. $12500
Smugness. Priceless.

Can't wait to continue modding.

About coasting in neutral... Transaxle damage? Max speeds? What are the dangers? How does the oil pump work? Is there some body of knowledge on this?

[Daox]

Its made to coast in neutral, no problems there. The engine will kick in if you exceed max speed. However, if you just use the gas pedal you should be able to shut the engine off pretty easily (once its warmed up). The technique is just let off the gas completely, then apply just a little pressure until all the arrows disappear on the MFD.

[bwilson4web]

Hi,

Originally Posted by orange4boy

. . .
About coasting in neutral... Transaxle damage? Max speeds? What are the dangers? How does the oil pump work? Is there some body of knowledge on this?

The following model showing the relationship between ICE, MG1, and MG2 rpm:

Toyota Prius - Power Split Device

The critical speed is 42 mph, 67 km/h. At or above 67 km/h, the control laws will keep the engine running. Regardless of vehicle speed, it is always OK to put it in "N" as long as the engine is running. So if I'm on a road where I want maximum glide, slip it into "N" and keep on rolling.

Below 67 km/h, the engine is optional, the hybrid operating range. Again, below 67 km/h, it is always OK to put it in "N". But if the engine is off and the car put in "N," it can no longer start the engine. The potential risk is putting the car in "N" on a down grade and having the vehicle speed increase over 67 km/h with the engine off.

As MG1 spins faster and faster, it generates a higher and higher voltage. There is a Dept. of Energy paper (ORNL/TM-2004/247) that maps the voltage vs rpm curve for the NHW20 (2004-2009) Prius showing what happens. The current hypothesis is that with the ICE not turning, the MG1 rpm above 67 km/h can generate voltages so high that the inverter could be at risk from over voltage. The nomographs suggests the following MG1 redlines:

• 6,500 rpm - NHW11 (2001-03) Prius
• 10,000 rpm - NHW20 (2004-09) Prius

My NHW11 has been up to at least 50 mph, 80 km/h, with the engine off and going down hill. Hobbit has done similar overspeed experiments with his NHW20. So the over speed failure isn't 'instant' but neither of us have a great interest in testing to find the absolute MG1 limit. In my case, if going down a grade and my speed increases to 42 mph or higher, I shift the car in "D" to get the engine started and back to "N" but that is how I drive.

The transaxle pump is driven by the engine. However, it is not a pressure based, lubrication system in the traditional sense. The gears and axles are OK with this. The only time significant stresses might occur is when the engine is at full power and then the pump will be turning.

One of the best collections of Prius knowledge is "Prius Technical Stuff," the Yahoogroup. It has message archives going back to 2000, the first NHW11 Prius in North America. Even now, there is a hard core group of Prius technophiles who hang there sharing experiments and addressing rebuilder problems. The files section includes photos, graphs, papers, and other studies ... an unusually rich source. It is the network version of Ecomodder specific for the Prius. FYI, it is 'first post moderated,' which keeps down the the SPAM.

Bob Wilson

[Daox]

In what cases do you use neutral coasting Bob?

[bwilson4web]

Hi,

Originally Posted by Daox

In what cases do you use neutral coasting Bob?

During the first 5 minutes or until the engine coolant reaches 70C and I can get it into Stage-4. For example, I cut through the neighborhood, relatively flat with 25 mph, 40 km/h, speed limits and I'll slip into "N" so the ICE will turn slower. Especially at stop lights where I'll shift into "N" to reduce the fuel burn while waiting for the light. My informal testing suggests stopping and starting the engine manually is more fuel expensive so I just idle in "N". If stopped and in "D", the engine will burn fuel a little faster than "N":


Once I'm in Stage-4, I pretty much just drive the car. Traffic permitting and I can safely use "N", I'll do it but I'm not really obsessive about using "N" to extend rolling. I used to drive a manual and was happy to push in the clutch when I wanted to roll w/o having to hold the accelerator.

Bob Wilson

[Daox]

I was under the impression that mechanically, drive and neutral are identical. Is that incorrect, or is there some other advantage I don't know about to coasting in neutral?

[bwilson4web]

Originally Posted by Daox

I was under the impression that mechanically, drive and neutral are identical. Is that incorrect, or is there some other advantage I don't know about to coasting in neutral?

Mechanically, you are correct. The magic happens with MG1 and the planetary gear. It is so different from ordinary transmissions.

In the Toyota hybrid transmissions, MG1 combines the function of clutch as well as variable gear ratios. The way it works is:

• no current flow - MG1 spins without resistance so the engine driven gears have nothing to 'push' against. This is the equivalent of neutral.
• generator mode - by allowing MG1 to work as a generator, it causes a reactive torque against the engine driven gears. With something to push against on the MG1 side, the engine gears can apply torque to the other side, the ring gear, that drives the wheels. The torque ratio is 28% to MG1 and 72% to the ring gear.
• generator mode normal - the power from MG1 races through the inverter and then feeds into MG2 that is on the ring gear side. So 72% of the ICE power flows through the ring gear and 28% slides around via the electrical circuit. Thus no power is lost except for some ohmic heating and normal gear losses.
• energy recirculate mode - at speeds around 25 mph, 40 km/h, MG1 slows down (check the earlier software model) and can no longer generate power and the resistance torque needed. At this point, power is taken from MG2 that is spinning and is fed to MG1 to work as a motor and make the torque needed by the ICE gears. But because of the gearing, this mechanical power combines with the ICE power on the way to MG2 where some is converted to electrical power to drive MG1.
• variable gear ratio - the MG1 torque is computer controlled by the current. By driving more current, the reactive torque looks like a 'taller gear' and the engine can deliver more power. Less MG1 torque looks like a 'smaller gear' so the engine can deliver less power.

Seriously, it takes an entirely different way of thinking to understand this transaxle. But the more I've studied, more I've come to appreciate what an engineering marvel it is.

Bob Wilson

[talonts]

Originally Posted by bwilson4web

Hi,

During the first 5 minutes or until the engine coolant reaches 70C and I can get it into Stage-4. For example, I cut through the neighborhood, relatively flat with 25 mph, 40 km/h, speed limits and I'll slip into "N" so the ICE will turn slower. Especially at stop lights where I'll shift into "N" to reduce the fuel burn while waiting for the light. My informal testing suggests stopping and starting the engine manually is more fuel expensive so I just idle in "N". If stopped and in "D", the engine will burn fuel a little faster than "N":

Ah, Bob, now I know how some of you guys get stellar mpg in your Prius while I "limp by" at about 45-48 ;-)

I've always know the topography matters a LOT, simply because my 04 got 50-52 when I lived 40 miles east, the only real diffs were limits and it was virtually flat there. Now 40 miles west, I get that 45-48 in either the 04 and 06 for daily driving. When I take the route to recycling that covers most of the route to my wife's work, I get close to her mpg in my 06 (50 on up to 60mpg) , and my size 16 foot makes it a LOT harder to control the pedal than hers.

I have a 0.2mi home street (no limit posted), a 0.2mi 30mph, then 2 miles of 55mph to get to a 65mph road. I have to take that to get to ANYTHING, and ANY shopping is 15mi or more away. My mpg tanks rapidly when starting out on a trip, and still drops a little on the way home due to that 65. It doesn't help that my car is used for virtually all shopping trips, so lots of stop-n-go with cool downs between.

My only other choice is the "back way" that never tops 55, and is nearly the same miles to the point where I would start shopping, so maybe I might have to try it for a couple of weeks to see how it goes. It probably takes 10min more, though, and I'm an impatient guy, so we'll see ;-)