Prius Doesn't Coast Very Far When You Let Off On The Gas

I suspect it's a lot easier to roll the car at 15 MPH than at 60.

 

So you're saying you think the same effect you described as "sudden braking" here:

should also be so negligible as to be indistinguishable at 15 MPH from the "neutral" behavior with power on?

 

While also making a Prius impossible to tow.

 

So. The motor is generating more heat when being powered or generating electricity. What isn't carried away by the transmission fluid will dissipate through the case.

This is from an article about actual magnetic braking systems, "A disadvantage is that since the braking force is proportional to the relative velocity of the brake, the brake has no holding force when the moving object is stationary, as provided by static friction in a friction brake, hence in vehicles it must be supplemented by a friction brake."
Eddy current brake - Wikipedia (it mentions the power tool use)

In a free spinning motor, it is merely a part of the drive train losses, and is made up for by having less friction and spinning gears when compared to an automatic transmission.

In fishing,casting reels have extremely free spinning spools. If left unhindered when the bait or lure hits the water, they keep going, with the line now not being pulled off you get a tangled mess. The magnets are on option to controlling that instead of a friction brake or your thumb. It can take fiddling to get working without too much braking, and requires adjusting when changing the terminal gear. I just use my thumb with a leather protector.

 

Well, the evidence is clear that Prius "neutral" is not just a freewheeling MG1.
If you choose to believe otherwise, it's your choice.

 

Of course, when people keep merging or braking in front of you, DRCC will not be as smooth as a skilled driver and result in worse fuel economy. What I mean is that DRCC is more fuel efficient than manual driving if the car is traveling at constant speed.

 

No one is saying that there is no magnetic braking at all. What people are saying is that it is negligible to the drag in the tires, drivetrain, and through the air. And, as it was said, even in a nonhybrid car, there is a drag in the transmission in neutral gear.

In fact, that is exactly how EPA measures the fuel efficiency—through coasting. They put the transmission in neutral to see how long the car takes to stop, and they get the total (aerodynamic, drivetrain, and tire) drag on the car out of that. (The coasting test on a road is followed by a laboratory dynamometer test once the total drag is determined through coasting.) As a matter of fact, I believe the drivetrain drag in a Prius is less than that in a nonhybrid car; so, again, the magnetic braking is negligible in comparison to other components of the drivetrain drag.

 

(Hopefully) coming back to the OP’s question:

There is actually a recent scientific paper on exactly what the OP wants, and it claims improved fuel economy if regenerative braking is reduced during coasting. I can’t download the paper; so, I don’t know if this technology (apparently reducing regenerative braking during coasting through software) is employed in the Gen 5 (or even Gen 4) Prius/Prius Prime and/or if it applies to a skilled driver.

https://www.sae.org/publications/technical-papers/content/2020-01-1195/

 

The Outback is my first car with DRCC. The doing better than CC experience is mostly driving without traffic.

Sounds more like a call for hybrid designers to make the car behave less like an automatic when foot off gas, and let it take more advantage of the neutral like coasting the car could do naturally.

 

DRCC in a nonhybrid vs. a hybrid is apples vs. oranges. It is true that in a nonhybrid, DRCC is not fuel-efficient at all. However, in a hybrid, it is equally fuel-efficient if not more in my experience. Hybrid drivetrains are a lot smarter than nonhybrid drivetrains when it comes to fuel efficiency.

 

Do you know anyone who is able to tow a Prius with the drive wheels on the ground?
I didn't think so.

 

Certainly, it must be more efficient to permit a car to coast than to convert the momentum into electricity then turn the electricity back into motion later. Realising that greater efficiency amongst other cars, speed limits and traffic lights often won't be possible.

In my city, there are a few long and steep descents into a university area that build momentum that can't be turned into any sort of distance because of school zones, blind turns and traffic lights. I've found that the level of regeneration introduced by just taking the foot off the accelerator maintains speed in the mid 20s, which is the legal limit. In car without regeneration, if neither gearing nor braking are used double that is the likely speed. Having the spare bit of charging is more useful.

I do have a long gentle descent I've used for years to measure rolling resistance of tires. Coasting from 65mph to the off ramp turn can vary from entering the turn from 50 to 35 mph depending on tire, inflation and weather. On that sort of descent, regeneration can absolutely get in the way. That kind of opportunity is rare in my area and it isn't the kind of opportunity for which a normal driver would look.

 

But, again, it is drive-by-wire and all about the pedal (brake and gas) modulation in an HEV/PHEV. Use the eco driving mode to get a lot more pedal precision (more range of travel) at low throttle, and it does not take much skill to control the pedal to coast however you like (net negative, positive, or zero force). You can also use the DRCC. Therefore, the OP's concern is a nonissue in my case.

The paper only applies to drivers with minimal or no hypermiling skills in operating an HEV/PHEV.

 

A 2005 Prius is in my pool of experience.

There are many cars you can't tow with the drive wheels on the ground. That doesn't mean you physically can't do so, but because it will damage the transmission.

 

So let's say, you're freewheeling along, with your MG1 turning effortlessly as you go.
What happens when the gasoline engine start up, as it's prone do do? Doesn't the system suddenly engage the MG1 backwards to compensate? Just askin'.

 

Pardon me, but doesn't that mean you can't?

 

If the job of Neutral is to deliver zero torque to the wheels, it can only manipulate the rotation of MG1 to do so. In Drive, it must do so to provide the desired amount of torque to the wheels. It's sheer silliness to say that MG1 is doing nothing while in Neutral.

 

The older Prius manuals told you not to tow with the front wheels on the ground, but people did it anyway. G5 manual is more relaxed.

The only real problem people have ever had with towing is how to get the parking pawl disengaged - shifting from P to N. You need to get the car into at least ON to do that, so if the 12V is totally dead you can be stuck. But once the pawl is disengaged, it rolls freely in N.

(And the pawl can be mechanically disengaged if the 12V won't co-operate, to let you tow a totally dead car, but it's a pain to reach).

 

Yes, it must provided the desired amount of torque to the wheels - zero (or at least negligable drivetrain losses comparible to any other car in N). Which it does by requesting zero torque from MG1 and MG2 - letting them both coast. The same as if the system is in N, including N while not in READY with the high voltage not active.

I'll try asking you again, see if I can get a response. Why are you only talking about MG1? Do you think MG2, bigger, attached firmly to the wheels, and turning at higher rpm, is exempt from your "motor-generators needs to be pushed" belief?

 

The engine isn't prone to start in N. That's one of its key characteristics, and why leaving it in N is a bad idea. It will discharge the HV battery, because it won't start the engine.

Because it needs MG1 to push to start the engine, and N is trying to keep MG1 and MG2 disengaged.

If the engine is already running in as you select N it will stay running, but still it won't charge the battery - the transmission is just freewheeling in neutral.

There is one exception apparently (not sure if this was there in all generations, but it is now) - it will briefly activate MG1 to start the engine if the vehicle exceeds the maximum EV speed. You'd have to be accelerating downhill in N.

But aside from that protection in that extremely unlikely edge case, it keeps the electrics disengaged.