Driving in bumper-to-bumper crawling traffic

8 mph is where you get the "0 arrow" glide on the gen III, otherwise there are arrows either going to the battery or from the battery.

While reading this thread, I'm realizing there are different interpretations of "bumper to bumper" traffic (and indeed there are different types of bumper to bumper traffic).

The worst is the 2 - 5 mph crawl. Ugh. Using battery power all the time, can't pulse with gasoline and you have to use friction brakes to slow down.

Better is the stopped to 8 mph stuff. At least you can pulse (a little) and glide a little. Stopping is bad, but if you pause after traffic moves you may get to pulse with the gas engine.

Even better is the 5 - 15 mph "Slow and Go", where you can pulse using the gas engine and then coast, but not have to come to a stop. The battery charge will usually keep up for an extended time and my never go down to 2 bars.

 

This is exactly what i mean, when your creeping your braking against the electric motor, which is causing the battery to drain even if you haven't moved much.

While in crawling traffic, I think it is more of a discharge issue (braking against electric motor's simulated creep), instead a charging issue.

On my usually way to work today, I tried going to neutral (after initial movement) i'm not sure if it did anything, the ICE did not go on. So it might improve mpg. But even when driving regular EV, sometimes the ICE does not go on.

 

this is interesting, are you saying that the motor is using energy even while stopped in drive?

 

While true on a normal car, the Prius doesn't work this way. A normal "dumb" automatic transmission tries to move the car forward when in D, whether you are braking or not. The Prius is smarter than that. When you lift your foot from the gas the power is cut from MG2. If you are moving MG2 will attempt a slight amount of regenerative braking to simulate engine drag.

When standing still with the brake depressed, MG2 receives no power. As you release pressure on the brake, MG2 is lightly powered to simulate creep as with a normal automatic. Press harder and the power is stopped. Power and braking are well coordinated.

Tom

 

But this is what we're saying.. with slow speed traffic, the motor is drawing current to push against your braking effort to give the creep simulation.

The triggers to cut/reduce that power surely have to be

a) an increase in speed (not wanted by the driver)
b) an increase in brake pedal effort by the driver ( assuming there is a brake pedal position sensor like the accelerator ?? )
c) lack of a need to increase the speed electrically ( eg downhill ) which would be "glide" or "coasting", or the ice kicking in for some reason and the ECU preferring ICE over motor.

So, in my theory, the ECU is constantly in a state of altering the motor power up and down "testing" the boundary limits.

I guess we could measure the MG torque readings in OBD for a given speed ( eg 5mph ) on a consistent level/gradient to show torque +/-

 

I understand what you are saying, but that's not how it works in the Prius. Saying it doesn't make it so.

Tom

 

Please feel free to share how it works, and your information source, since you evidently have access to the information ?

 

The simulated creep is the culprit.

Is there a way to disable the creep, and make it so it only moves when you push the gas?

 

no.

 

This has been discussed many times before. Our information source is the Prius Chief Engineer, whom we grilled in Detroit. He was a wealth of information, as you might expect. We have also collected a lot of additional information through instrumentation and experimentation.

On a regular manual transmission, the engine attempts to push the car forward all of the time while in D. The torque converter allows it to slip, but it is still trying to move forward. Only the brakes keep the car from moving. When creeping forward, the brakes slip, dissipating part of the energy. Additional energy is dissipated as heat in the torque converter. The remaining energy is used to push the car, doing useful work.

The Prius is moved at a low speeds by the main electric motor, MG2. Both this motor and the brakes are under full computer control. When the driver presses firmly on the brake while the Prius is stopped, the computer recognizes that no motion is wanted or necessary. The mechanical brakes are applied and power is cut from MG2. No power is wasted as it would be with a normal automatic.

To get the Prius to creep, the driver releases pressure on the brake pedal. The computer releases the friction brakes and applies a small amount of power to MG2, causing the Prius to creep forward. Once again, no power is wasted.

There is a small point in between where the friction brakes are applied while a small current is sent to MG2. You can see this with the power monitor or with Scangauge, where power flow to MG2 is indicated but the Prius isn't moving. This is technically the power wasting point that so concerns you. In practice the amount of power being sent to MG2 is nearly zero, so it is of no practical importance. If you want to avoid it, don't sit with the brake lightly applied.

Tom

 

#2 and #3 above are the same thing. #1 and #4 are the same. In a regular Prius (not plug-in), there are only two ways to charge the HV battery: regenerative braking and the ICE. In truth regenerative braking is also powered by the ICE through the kinetic energy stored in the car, but that's getting into more of a physics discussion.

The ICE on a Prius runs for a variety of reasons: 1) To provide motive power, 2) To make heat, and 3) To charge the HV battery. Any of these three can cause the ICE to run, but when it does, it often services more than one condition; in other words, if you have to make heat, you might as well charge the battery.

Getting to the question of which charging method is most efficient, we need to go back to the source of all power in the Prius: the ICE. All energy in a conventional Prius comes from burning gas in the ICE. In descending order, the most efficient use of gas for moving a Prius:

1) Direct propulsion by the ICE.
2) Electrical propulsion from the ICE via MG1 and MG2.
3) Electrical propulsion from the HV battery.
4) Electrical propulsion via regenerated electricity.

The key to understanding this list is that each one adds an additional conversion step to the process:

1) Chemical energy is converted to mechanical energy via combustion.

2) Chemical energy is converted to mechanical energy via combustion. The resultant mechanical energy is converted to electrical energy by MG1 and converted back to mechanical energy by MG2.

3) Chemical energy is converted to mechanical energy via combustion. The resultant mechanical energy is converted to electrical energy by MG1 and the electrical energy is converted into chemical energy in the HV battery. This chemical energy is later converted back into electrical energy by the HV battery. The resultant electrical energy is converted back to mechanical energy by MG2.

4) Kinetic energy is stored in the moving car by some combination of the above three methods. This kinetic energy is converted to electrical energy by MG2 and converted into chemical energy in the HV battery. This chemical energy is later converted back into electrical energy by the HV battery. The resultant electrical energy is converted back to mechanical energy by MG2.

Each conversion step wastes some energy. So why even bother with the expense, weight, and complexity of a hybrid system? The answer is that the alternative is often even more inefficient. Regenerative braking is inefficient, but friction braking is 100% inefficient. The electrical power path through a Prius is inefficient, but a conventional automatic is often even more inefficient. The hybrid system doesn't make it more efficient, it makes it less inefficient. I know that's a quibble, but it will help with understanding if you think of it in this manner.

As for the final question of why the Prius applies some regenerative braking when you lift your foot from the gas, the answer is that it does so to simulate engine drag in a normal car. It would be better to not do this, but then the Prius would not feel like a normal car. Toyota was careful to make the Prius as normal as possible in terms of operation. The same is true for automatic creep. It exists in the Prius just to mimic conventional cars.

Tom

 

I wish there was an Easter egg, to shut off the regen, and creep. Both adds an unnecessary energy conversion step. Because if we want to slow down we just step on the break, and when we want to speed up step on the gas pedal.

Someone figure out the Easter Egg, to turn off auto regen, and sim creep. There has to be one… like hold the EV button down for 30 second, beep the horn, then open the hood, turn on headlights, all while putting your left index finger on your nose.

Other words turn on glide mode. I’m perfectly fine with this, as this is the way I drive my 5 speed Insight.

 

To apply this knowledge to the OP's situation and working with what we have available to us:

When accelerating:
Force the ICE to fire up by getting to the right side of the HSI, but stay out of the power zone. My observations are that this charges the HV at rates of around 10 - 20 A.

When slowing down:
a) Glide - I try to keep BTA at 5 - 10 A.
b) Coast
c) Regenerative brake

The choices are in order of relative efficiency. Which one I choose depends on traffic conditions and SOC.

As SOC drops close to 40%, I know the ICE is about to start up, so I start doing the above to raise/maintain the SOC. The logic to me is that if the ICE is going to start up, I might as well get some propulsive force from it ('most efficient' or 'least inefficient' - see above).

If the traffic conditions get so bad that I can't even accelerate with ICE, then I've found it's usually too late to avoid the ICE eventually charging up the HV without propulsion (least efficient). Leaving a bit of a gap between cars sometimes works.

It does help to have a higher SOC before entering such traffic conditions, but it's hard to influence this as the Prius aims to keep this around 60% in open roads. Once I hit bad traffic SOC soon falls below 50% with 'normal' driving. I start doing the above if I don't think the traffic will clear before it gets to 40%.

We have a highway over here (we call them motorways) called the M25 which is also known as our largest parking lot. I get to practise this a lot in my commute home!

 

The hybrid system allows you to absorb short periods of bumper-to-bumper traffic by using some of the energy which would have been lost as heat. Depending on conditions, it may take about a mile or 10-15 minutes of very slow bumper-to-bumper traffic for the SOC to fall to a level where the ICE kicks in.

If you are aggressive about keeping the SOC up, and lucky, it is possible to defer this episode of inefficiency long enough for the traffic to clear.

A typical example was with my commute home last night:
35 miles, mostly on the slow moving M25. The 'variable speed limit' traffic calming signs were on, mostly set at 40 or 50 mph. These are perfect conditions for varying between P&G, WS and SHM in different lanes, before hitting segments of bumper-to-bumper traffic.

http://priuschat.com/forums/gen-iii...ent.php?attachmentid=34943&stc=1&d=1329582276

Air Temp: 10 C (50F); tyres pumped; grill blocked
Consumption in mpgUK, probably an over-estimate; Scangauge figure for this journey was 61 mpgUS

I should state this is not dull driving with the brain switched off listening to the radio. More like fully alert, total concentration, needing thoughtful anticipation, judgement & quick reactions. For me, the added instrumentation of SGII allows some extra precision which sets up a driving mindset that is nicely placed away from boredom on the one hand and anxiety on the other.

[Strangely similar to the kicks I got many decades ago when I was (sadly) a boy racer in a sports car and when we had open roads!]

 

Put it in neutral.
[edit]Note: when in neutral and ICE runs, the only thing it can do is GENERATE HEAT. It will NOT charge the HV battery![/edit]

 

To effectively counteract the effect of creep or regenerative brake on glide, one option is to guide your use of the brake or accelerator pedal while monitoring current drain from the HV battery with extra instrumentation like Scangauge (e.g., the Xgauge: battery current).

By watching this you can be reassured to know when the car is not trying to creep and you can be more precise using the accelerator pedal to cancel out regenerative braking.

 

jugst don't hit the car in front of you whilst watching the gauge.