Running Out of Gas

Two bars left can happen in normal use so your friend did not stress the traction battery. No harm; no foul.

JeffD

 

I am guilty of running out of gas and then using the battery for ~2 miles or more to get to the nearest gas station. On 2 occasions i ran the battery completely flat(no bars). After waiting a few minutes i was able to restart the car, let it idle for a minute until the little bit of gas that was left in the tank recharged the battery a bar or two, then continue driving again.

I have not had any ill effects, although i m able to fill ALL the bars green on the battery meter(I wasnt able to before).

FYI the car is at 144,000+ miles right now, no problems yet....

 

It shouldn't be difficult or problematic to go 2 miles on electric if the terrain is flat (or downhill) to the station, you don't have to make multiple stop/starts, and you start with a normal charge. Shut off all accessories except hazards, do a gentle acceleration to a low speed (say 25-35 mph) then glide down coming into the station.

I do a 1.1 mile all EV acceleration and glide on the flat from a stop to a stop (with a few 90's and about a 10 foot rise for a railroad crossing that I have to brake for then accelerate again) and it only burns 1 bar doing so. Granted this is on a new battery/new car and a disproportionate amount of charge is in that one bar. The car will glide a very long way from 30 mph as long as the terrain is flat, so once up to speed it doesn't take much to maintain it.

I don't know what the "sweet spot" speed is for low speed in EV/glide. I imagine that it is somewhere between 25-35 mph and that running slower will result in greater tire friction losses or more sensitivity to very slight grades.

 

Efficiency testing has shown the hybrid-electric, maximum range speed to be in the 18-20 mph range. I doubt the maximum electric-only range speed is higher than 18-20 mph because the range limit remains the 'heart beat' or fixed overhead.

Elimination of all excess load is key to maximum range. In theory, pulling the fuses for the headlights might add a little range but if you're at this point, you're at 'rearranging the deck chairs on the Titanic.'

GOOD LUCK!
Bob Wilson

 

Note to all who cruise extended periods of time on the battery only: Toyota does not recommend that behavior. It seems the Hybrid Synergy Drive (planetary system) gets its lubrication from an oil pump drived from the gas engine. So, when the engine is off, there is no lubrication to the HSD. Toyota doesn't say how far you can run on electric only, they just say 'extended' periods are not recommended.

 

Bob,

I'm not disputing the speeds you've stated, but wouldn't the above have the opposite effect? The higher the fixed overhead (lights, MFD, ECU's, etc.) the more benefit there would be from running a little faster. Fixed overhead would be the hourly energy expenditure just for having the vehicle on, correct? For example in "glide only" the vehicle should cover more distance on a given charge expenditure for that overhead at 30 mph than at 20 mph or 10 mph. I made note of the average speed effect when calculating the mileage hit from running the headlights during the day.

 

This is true. Take the first derivative and set it to zero to find the optimum speed.

Tom

 

I'm pretty sure the part about the lubrication is wrong as the system would be damaging itself whenever the ICE was off (glide, regen, or electric.) ICE off operation is fundamental to the hybrid system. Besides, European vehicles have an EV mode.

The concern is with drawing the battery to low SOC's repeatedly. The more times one cycles the battery hard and the wider range it is cycled over, the sooner the battery will fail. That is my understanding. For this reason Toyota's management system attempts to keep the SOC within a defined range, temperature, etc.

The worst conditions would seem to be daily long steep mountain climbs where the battery is going to reach a low state of charge, then on the other side it is likely to be charged to the maximum (regen) that the control system will allow. That would exercise the battery to its max.

 

Assuming the data picked up by the ScangaugeII from the CAN-bus is accurate, overhead draw seems to be just a little over 1 Ampere.

One issue, then, would be balancing reducing the impact of that overhead against increased air drag loss for a given speed increment.

Both are pretty small, so it may be that some other changes dominate instead. One obvious one is that the resistive loss fraction of energy expenditure must surely go up at higher motor currents. It would be really interesting if someone has actual data on whether this becomes important enough to set the maximum range speed sooner than the non-linear increase of air drag does so.

One thing seems consistent--away from hypermiling hangouts, almost all drivers seem to overestimate their most fuel-efficient cruise speed.

 

Regarding HSD lubrication, see these:

Yahoo! Groups

Prius Hymotion Plug-In Conversion

 

EZW1,

Thanks for the info. The HSD is still getting lubricated when the ICE is off but spinning at 42+, and below that there is a limited distance it can travel with the traction battery before the ICE starts anyway. So the point is moot for any mode of operation we are discussing. Even the second link which is for a plug in conversion says, "It is already pretty clear that the bearings [the majority of which are ball or needle, so they're already very low-friction] stay adequately lubricated over long periods of engine-off time."

I'm still not sure where your statement from Toyota originated, as they have an EV mode switch in Europe. The only time this appears to be even a possible concern is if you have a plug in conversion and go many cycles without running the ICE at all.

 

Another question about adding gas when running out; I've read there is a minimum needed to add before the engine will start, believe it's around 3 gallons. Has anyone found out if pulling out a main engine fuse will have any effect on this required amount. I'm wondering if this might wipe out the memory of fuel needed. I would try AM2 : Blue 15 amp fuse in right side main engine fuse box. ( fuse names are listed underneath the black fuse cover fuse) since that fuse once caused my car to appear 'dead'. I'm interested in a way to be able to just add 1 gallon to the car, that's easier to carry. Also , wondered if anyone has hacked into the actual values of the fuel tank sender, before it gets misinterpreted by the computer/ gas gauge. Thanks in advance