800+ Mile Club

Not sure why he called me that. Only have about 8k and we bought it in April. And that's including a BIG road trip.

 

Prius orthodoxy diverges here. You are using battery energy that will have to be replaced later, along with conversion losses. Unless those losses improve drivetrain efficiency by an even greater amount, I cannot see where the benefit is.

I personally shoot for minimal battery use in city driving. Two occasions I rely on battery power:
1. Moving from a stop when I do not expect to fire up the ICE at all before I stop again;
2. A little extra juice to my glide to make it to an anticipated stop.

 

Is there a way to prove this with data -- say, using Torque ?

I can accept the ICE ramp up to desired rpm speed is inefficient, but that is going to happen anyway, sooner or later for the case we are discussing. Unless the ramp up is more efficient when the car is moving, I am still at a loss to see why it is better (more efficient.)

I have gotten in the habit of taking a few seconds to move rpm from 0 to 2000, although this is more to keep the ICE quiet. I wonder if it matters to efficiency.

 

I was thinking more along the lines of summing fuel injection vs amps to compare ICE vs battery conditions. That would give you a range of ICE average efficiency required to at least match battery only energy use.

I understand ICE efficiency to mostly be related to torque and rpm. Why does car speed matter ?

 

Thanks for the link Justin.
I enjoyed the read, although I admit I skipped the posts of a certain member.

Qbee had something interesting to say, that at low speeds most of the ICE torque is routed through the electric pathway anyway. While Wayne Gerdes is the king of empiric methods, I always feel much better about a technique after Qbee or Hobbit explain why it works

I can tentatively accept that stomping on the fuel pedal from 0 to 2500 rpm from a stop is not efficient. I wonder how a slow stomp on the fuel pedal over a second or two compares. As it is, the car naturally has an EV only period at the start of acceleration from a stop. We are arguably only discussing an optimal car speed before the ICE kicks in.

 

Fair enough; I doubt there is enough difference in practice between us to make a measurable difference in fuel economy. I would like to find a description of 'gentle acceleration' that distinguishes between accelerating at e.g. 1500 rpm until glide speed in obtained, vs a slower ramp up to a higher rpm pulse of say 2000 rpm.

Why split hairs, when you can ponder the second and third derivative ?

I dally on this point because it matters to other drivers

 

And that is coming from someone who had done both (and can't be "pooh poohed" with a dismissive wave and a patronizing statement of you never having driven a "real" car before).

 

Wow this is impressive! Over 800 miles(!) I assume you had 100's of pissed of drivers following you, speeding around you and beeping at you.. that you passed at the gas station... a couple times! Well done!

 

Actually one of my goals is hypermiling is to be as respectful as possible when doing so. So...no one ever had to follow me. I pretty much drive with the flow of traffic.

 

The electric motors only have so much torque/power so on some uphill grades the Prius doesnt allow you to use the EV mode from a dead stop. On the other hand, at some traffic light stops with a steep downhill grade the Prius can accelerate in EV mode up to 25 mph and if gently accelerated the Prius can continue to accelerate up to 45 mph using only the electric motors in normal mode. The reason Gerdes is recommending using electrical power during the dead stop acceleration is because the Prius needs to regularly use the electrical power it has generated to get the most efficient use out of its limited HV battery capacity. The Prius battery power capacity is not that big and once the battery gets full (SOC = +75%) then it cannot store any more excess braking energy --- so to keep the battery levels low enough so it can readily absorb the braking energy - the Prius needs to use the electric power on a regular basis to prevent the battery SoC from getting too high. IsTM - The most efficient use of electric power is when it is used to extend a glide phase in a P&G cycle. However, I think one of the more *fun* things to do on a Prius is to accelerate downhill from 0-45 mph using only the electric motors.

 

The SOC never reaches full in level driving, or even driving rolling hills. At least for my driving patters, the SOC is more likely to hit low than high due to my tendency for extended glides.

I am skeptical this is Wayne's reason for starting out in EV, but a choice quote would convince me

 

I too personally don't think this is Wayne's reasoning. I think it's very simply that the electric motor is more efficient at those speeds.

 

In a more or less flat driving environment, I think Wayne's recommendation for starting out in EV will work out.
However, in more hilly driving environments, Wayne's use of speed to dictate energy usage is not doable.

I am absolutely sure that torque and not speed is more signficant deciding factor whether a 2010 Prius will allow the electric motors to run without the gasoline engine running. To my misfortune, I live is rather hilly area and I have some traffic intersections[1] where even if the HV battery has a SoC of 60% - from a dead stop, I will be lucky that the electric motors make over 7mph before the Prius switches over to the gasoline engine to climb uphill. I finding on some uphill starts where there is not enough flat road segment to get up to speed that it is best to just use to electric motors to overcome the initial inertia and rolling resistance -say use the electric motors only up to 5 mph and then switching over to the gasoline power at +1.0 gph/+1200 rpm as soon as possible. However, for every uphill there is a downhill -- so there are also traffic interesections where I can get my Prius can go from 0- 45 mph on downhill grade with only electric power .[2]

The Prius SOC is never suppose to reach over 80%; this limitation creates a safety margin to prevents the battery from overcharging, makes it easier for the batteries to recharge(*), and it supposedly extends the lifespan of the HV battery. On my annual trips from Maryland to Michigan when I cross PA (I-80) I come across some steep downhill segments where generative braking on the downhill can sometimes push the HV battery SoC over 75% (fyi - my highest SoC reading was 78% which got me 8 bars on the HSI display). When this happened, my 2010 Prius disabled the Cruise Control while it was going downhill and operated only using the electric motors at speeds greater than 60 mph ( btw - this phenomena occured in normal mode with the tranny in D). During this episode, the Prius electric motors spin very fast and are very loud as they aggressively try to use up the battery power. Only when the SoC dropped below 70% does the Prius restore the Cruise Control functions. It scared the begeezes out of me at the time because I thought I broke the Cruise Control somehow.

(*) batteries donot recharge linearly. As the State of Charge (SoC) gets higher it takes longer to recharge and it takes more current to to recharge. By avoiding recharging the top 20% of the battery capacity - Toyota speeds up the recharging time characteristics of the battery.

[1] starting from a dead stop going north bound on Maryland Route 97[georgia avenue] at the traffic light at Maryland Route185 [Connecticut Avenue] and continue until the traffic light at Bel Pre Road.

[2] starting from a dead stop going Southwest bound on Maryland Route 28 [ Norbeck Rd] at the traffic light at Baltimore Road . Use only the electric motors accelerate up to 45 mph then switch to ICE to nudge the speed up to 50 mph as you go over Rock Creek (part of Lake Needwood Park/Rock Creek Park system) Bridge which is at the bottom of the hill then lower the throttle so the ICE is burning 1 gph as it climb uphill where you will lose up to 15 mph in speed by the time you reach the traffic light at Avery Road.

 

This was really really scary to do - but I overcame my fears and did it.
An 800 mile tank on a Prius with only Gasohol!
We need to keep Sir Drivelot company!



Vehicle: 2010 Toyota Prius III, Blue Ribbon
Tire make model: Yokohama Avid S33D 15 inch
tire Pressure: 48 psi front/46 psi rear
Modifications: 2 scangaugeII (IGN, TPS, AVG, FwT/MPG)( SoC, FLv, GPH, RPM)
Driving Techniques: DWB, DWL, P&G, SHM, SWM, rabbit timing, smart braking, Potential Parking, time shifting, ridge riding, no AC/defroster, no grill blocking
Driving temperatures 66 F to 95 fahrenheit degrees.
Max Speed: 50 mph, target top speed is 30-40 mph most of the time
Driving environment: Urban-Suburban stop and go or slow and go.
Driving mode: Normal or EV.
date driven: July 30th to August 28th 2012
odometer: 2562o to 26420 miles
distance driven: 800.1 miles (trip odometer)
gallons at fill up: 11.252 U.S. gallons, 87 octane (regular) 10% ethanol/Gasohol
MFD average speed estimate = 19 mph
MFD Fuel efficiency estimate = 73.4 mpg
Calculated MPG at the pump = 71.1 mpg
First Fuel Gauge Bar started blinking and beeped @ 658 miles
Miles To Empty reached zero(0) @ 689 miles