How to improve Highway MPG?

[lolder]

Drafting behind a big vehicle like a Semi is too nerve wracking even at the car-length-per-10 mile-per-hour standard. You can, however, see several mpg at a reasonable distance even behind a SUV.

[rfruth]

Truckers know what your doing & some of um don't like it (they can't see you in their mirrors) most 4 wheelers have no idea, all they know is someone is on their tail for no reason (now if you see um at a pit stop or you both have a CB radio you can let them know whats going on) 4 me the risk isn't worth the rewards - I stick to the right lane & a sane speed.

[Buster1]

Drafting really works. Of course it is illustrated by watching any auto racing. The Mythbusters did a test on it too (they really do use some good scientific theory of testing) and found it to be significant the closer you get to the lead vehicle. Just be careful.

 

Also, if you want...tape up all your hood and panel seams with some painter's or masking tape. I'm not kidding. Drive a week with and without it over the same hwy route and you'll see the difference.

[Oman]

It is far more complex than that. The gauges only tell you about what is going in and out of the HVB. They do not tell you what is going on between MG1 and MG2. MG2 is always either generating or consuming power. The computer decides if this power is going to go to/from the HVB or to/from MG1. MG1 is also always generating or consuming. When the ICE is idle MG2 can't contribute to wheel power. It consumes a small amount of power spinning at just the right RPM to make sure the ICE stays still. Only MG1 can contribute motive power. With the ICE idle the power that MG1 is allowed to consume is limited to the power stored in the HVB. The computer limits the draw to far below the maximum that the HVB could provide because drawing at maximum would greatly reduce the life of the HVB. MG1 is actually sized to be able to draw from both MG2 and the HVB at the same time since under heavy acceleration it will have both sources. The top speed of 47Mph EV is imposed because MG2 is essentially the transmission. It is only capable of spinning so fast before it risks damage. That spin speed is the difference between the ICE RPM and the final drive RPM. That is also the reason that MG2 is always either consuming or generating power. When the ICE RPM is higher than what is needed at the final drive (heavy acceleration) MG2 allows itself to spin therefore allowing a higher ICE RPM but with carefully controlled drag. This drag is created by generating electricity. This electricity plus what is stored in the HVB is used to augment what the ICE put putting out and sent to MG1.

 

At highway speeds MG2 is actually consuming electric power in order to keep the ICE RPM low compared to the final drive RPM. If there is a lot of spare power in the HVB it will be used but that will quickly be depleted so in reality at highway speeds MG1 is actually dragging a bit to generate electricity to keep MG2 spinning under power. That is one of the reasons that the car is less efficient at highways speeds than one might expect. There is loss at each stage of this power round-trip. But doing this is more efficient than letting the ICE spin at a higher RPM than it needs to. With Atkinson cycle engines you always want to be at the lowest possible rpm.

 

The software to keep track of all this and figure out microsecond by microsecond what combination of power routing and RPMs will be most efficient is pretty amazing.

 

 

 

BTW: Classically the word "Engine" was used to describe something that used an external fuel source and "Motor" was used to describe something that uses an internal or electrical power source.

 

 

I mentioned before "drafting at a safe distance" only.

Whenever there is ample power demand, Ford wants the ICE to run, not the electric motor (they are called "motors", not "engines"). The EV is used for transient acceleration pulses until the computer can increase the ICE rpm for more power.

It is also used for regenerative braking, and duty-cycling the ICE on and off at lower speeds for better efficiency. You can only see the power of the traction motor in reverse. Go to a big open area and carefully, briefly floor it in reverse. The ICE will probably start but it cannot provide power to the wheels in reverse. It can generate electricity which together with the HVB will power the traction motor in reverse. The power is substantial. You can't do this in "D" because the software won't permit it. EV mode is LESS efficient when higher power is required. This is a gas powered vehicle, not electric. The EV components only assist the ICE in efficiency. Plug-in-hybrids are completely different in requirements than the FFH and Prius.

Edited October 25, 2010 by Oman

[lolder]

It is far more complex than that. The gauges only tell you about what is going in and out of the HVB. They do not tell you what is going on between MG1 and MG2. MG2 is always either generating or consuming power. The computer decides if this power is going to go to/from the HVB or to/from MG1. MG1 is also always generating or consuming. When the ICE is idle MG2 can't contribute to wheel power. It consumes a small amount of power spinning at just the right RPM to make sure the ICE stays still. Only MG1 can contribute motive power. With the ICE idle the power that MG1 is allowed to consume is limited to the power stored in the HVB. The computer limits the draw to far below the maximum that the HVB could provide because drawing at maximum would greatly reduce the life of the HVB. MG1 is actually sized to be able to draw from both MG2 and the HVB at the same time since under heavy acceleration it will have both sources. The top speed of 47Mph EV is imposed because MG2 is essentially the transmission. It is only capable of spinning so fast before it risks damage. That spin speed is the difference between the ICE RPM and the final drive RPM. That is also the reason that MG2 is always either consuming or generating power. When the ICE RPM is higher than what is needed at the final drive (heavy acceleration) MG2 allows itself to spin therefore allowing a higher ICE RPM but with carefully controlled drag. This drag is created by generating electricity. This electricity plus what is stored in the HVB is used to augment what the ICE put putting out and sent to MG1.

 

At highway speeds MG2 is actually consuming electric power in order to keep the ICE RPM low compared to the final drive RPM. If there is a lot of spare power in the HVB it will be used but that will quickly be depleted so in reality at highway speeds MG1 is actually dragging a bit to generate electricity to keep MG2 spinning under power. That is one of the reasons that the car is less efficient at highways speeds than one might expect. There is loss at each stage of this power round-trip. But doing this is more efficient than letting the ICE spin at a higher RPM than it needs to. With Atkinson cycle engines you always want to be at the lowest possible rpm.

 

The software to keep track of all this and figure out microsecond by microsecond what combination of power routing and RPMs will be most efficient is pretty amazing.

 

 

 

BTW: Classically the word "Engine" was used to describe something that used an external fuel source and "Motor" was used to describe something that uses an internal or electrical power source.

Precisely. Toyota describes the main traction motor as MG2 and the planetary sun gear motor as MG1. Do you think Ford is different ?

[mort]

Hi Oman,

This is great... but your use of MG1 and MG2 are reversed from the convention seen here. I'd wished they had used transmission and traction.

-mort

[Oman]

I know. Many documents talking about the Ford system use MG1 as the traction motor... maybe a mistake taken to convention? Unfortunately traction and transmission have even the same 1st three letters!

 

I did notice that the hybrid info display actually eludes to the operation I described above. If you look at it while driving at highway speed you will see a set of lines moving from the ICE to the traction motor. The width of the line varies a bit seemingly indicating the amount of current moving in that direction. The flow in that line will switch directions when you slow indicating that the planetary drive motor is now requiring power. It doesn't show the detail as to the source or sink because it only shows the HVB going to the traction motor. But it does show that electrical energy is being transferred between the traction and planetary drive motor one way or the other at just about all times.

 

(note the change in convention used above :>)

 

 

Jon

 

 

Hi Oman,

This is great... but your use of MG1 and MG2 are reversed from the convention seen here. I'd wished they had used transmission and traction.

-mort

[lolder]

I know. Many documents talking about the Ford system use MG1 as the traction motor... maybe a mistake taken to convention? Unfortunately traction and transmission have even the same 1st three letters!

 

I did notice that the hybrid info display actually eludes to the operation I described above. If you look at it while driving at highway speed you will see a set of lines moving from the ICE to the traction motor. The width of the line varies a bit seemingly indicating the amount of current moving in that direction. The flow in that line will switch directions when you slow indicating that the planetary drive motor is now requiring power. It doesn't show the detail as to the source or sink because it only shows the HVB going to the traction motor. But it does show that electrical energy is being transferred between the traction and planetary drive motor one way or the other at just about all times.

 

(note the change in convention used above :>)

 

 

Jon

Do the hypremilers call this "negative-split-power-mode" where the traction motor generates power for the transmission motor to lower the final drive ratio and ICE rpm?

[Oman]

Stupid name but yes. A more accurate name would I think might be power shunt mode. The power used by the transmission motor is not lost, it still ends up back at the wheels. So in essence the ICE and the transmission motor are both providing power to the wheels but some of that is being taken by the traction motor to feed back in to the system. That is why the efficiency of the motors and power controller are more important than the efficiency of the HVB. Only a portion of the power that travels through the system ever makes it into the HVB for storage.

 

 

Jon

 

 

Do the hypremilers call this "negative-split-power-mode" where the traction motor generates power for the transmission motor to lower the final drive ratio and ICE rpm?

[VonoreTn]

Wow Oman,

 

You really understand this gear ratio thing, I'm a mechanical engineer and can't quit follow how you can change gear ratios with a planetary gear setup. Normally you would need some kind of variable speed device like a variable size pulley mechanism they use in motor scooters and some lawn mowers. I've been playing with the mg1, mg2 animation that Mort supplied (below), and starting to get the idea of how it works, but it is still confusing.

 

http://eahart.com/prius/psd/

Edited October 27, 2010 by VonoreTn

[Oman]

There is a reason that it makes so much sense to me. A long time ago I was involved in a project to design a better constant velocity transmission. Essentially this device takes the unbelievably wide RPM ratio from a turbine engine and keeps the output shaft turning at a near constant RPM to drive a generator. It happens that the best design we tested (using simulation software then a real prototype) was a large planetary with an electrically driven sun. These are used to today on jet aircraft.

 

And they also are 2/3 of the hybrid drive system we have in the FFH.

 

I wasn't directly involved with the engineering of the device itself rather the hardware and software that drove the simulations. That however got me pretty darn familiar with the concepts.

 

If I am trying to explain how this works to someone unfamiliar with them I actually start by explaining how the planetary gear works in an automatic transmission. By simply locking one part of the planetary you change the input and output ratios in the other parts compared to when it is free spinning. Once they get that you simply say instead of free or locked you spin it under power from a motor. The amount of spin changes the effective input and output ratios just as lock and free did but with an unlimited range in between.

 

Jon

 

 

 

Wow Omen,

 

You really understand this gear ratio thing, I'm a mechanical engineer and can't quit follow how you can change gear ratios with a planetary gear setup. Normally you would need some kind of variable speed device like a variable size pulley mechanism they use in motor scooters and some lawn mowers. I've been playing with the mg1, mg2 animation that Mort supplied, and starting to get the idea of how it works, but it is still confusing.

[lolder]

Also, the geometry of a planetary gear set determines the fixed ratio of torque that is shared or divided. By varying the sun gear motor/generator between motor and generator in either direction of rotation, they can do almost anything with the power inputs and outputs of the transmission. They can do with electronics what the 6 and 8 speed transmissions aspire to do. They do almost all the same thing the Volt does without 3 clutches!

[VonoreTn]

Also, the geometry of a planetary gear set determines the fixed ratio of torque that is shared or divided. By varying the sun gear motor/generator between motor and generator in either direction of rotation, they can do almost anything with the power inputs and outputs of the transmission. They can do with electronics what the 6 and 8 speed transmissions aspire to do. They do almost all the same thing the Volt does without 3 clutches!

 

I am starting to get it. MG1 is motor generator 1, which is connected to the sun gear. MG2 is the second motor generator set, which is connected to the ring gear, and the ICE is solidly connected to the planetary gear arm. And by varying the two MG's either as support of the ICE or load on it as it generates electricity, you can keep the ICE in an optimum state of RPM and load. The rpms are related by:

 

[N sun X rpm sun + N ring X rpm ring] = [N ring +N sun] X rpm arm

 

Where N is number of teeth in each gear. Given all this, the computer guys can go crazy optimizing ICE loads and support, with a goal of keeping the ICE in the maximum efficiency mode.

 

While I only have a superficial grasp of this strategy, my FFH with 23K miles averaging 39+ mpg is a testimony to the success of this approach so far. That's not based on my FFH gauges, that's based on recording every ounce of fuel I have put in the vehicle.

 

Also this strategy, basically initially invented/embraced by Toyota in their Prius offers a whole new world of FE potential for every car in the world, that is probably competitive with fuel cells and other previously proposed technologies for FE. While fuel cell cars are superior for electricity generation, they have large hurdles to catch up with this system, including weight, energy conversion from battery to motors, and the hydrogen supply infrastructure.

[lolder]

Patents by TRW, Antonov and Solomon have been the subject of patent lawsuits some involving Toyota. They involve manipulating power with two or more motors with a CVT planetary gear set. The idea is not new. Toyota in the 90's decided to refine it, produce it and sell it at a profit. It was difficult for them and risky. They are to be given credit for it. They are not the inventor of the system but I guess they have some patents for innovation. Making it operate smoothly, reliably and efficiently is the charm.

[Oman]

Don't put the traction motor into the equation. Just look at the ICE, MG1, and then the output of the ring gear. MG2 is just adding (or stealing) power to the output. The thing that makes it work so well is that MG1 is capable of turning at up to 6400 RPM - In either direction. That means a total of 12,800 RPM range on the sun gear.

 

That is one reason the "whrrr" or whistle that you sometimes hear on the FFH does not seem to match either the ICE RPM or the vehicle speed. Rather it is a function of the two. When you are accelerating the computer might actually start dropping the RPM of the ICE while the car is still increasing in speed. It can do this by decreasing the speed of MG1 thus changing the whirring sound you hear (seeming to move down in frequency). Neat stuff.

 

Jon

 

 

I am starting to get it. MG1 is motor generator 1, which is connected to the sun gear. MG2 is the second motor generator set, which is connected to the ring gear, and the ICE is solidly connected to the planetary gear arm. And by varying the two MG's either as support of the ICE or load on it as it generates electricity, you can keep the ICE in an optimum state of RPM and load. The rpms are related by:

 

[N sun X rpm sun + N ring X rpm ring] = [N ring +N sun] X rpm arm

 

Where N is number of teeth in each gear. Given all this, the computer guys can go crazy optimizing ICE loads and support, with a goal of keeping the ICE in the maximum efficiency mode.

 

While I only have a superficial grasp of this strategy, my FFH with 23K miles averaging 39+ mpg is a testimony to the success of this approach so far. That's not based on my FFH gauges, that's based on recording every ounce of fuel I have put in the vehicle.

 

Also this strategy, basically initially invented/embraced by Toyota in their Prius offers a whole new world of FE potential for every car in the world, that is probably competitive with fuel cells and other previously proposed technologies for FE. While fuel cell cars are superior for electricity generation, they have large hurdles to catch up with this system, including weight, energy conversion from battery to motors, and the hydrogen supply infrastructure.

[VonoreTn]

Patents by TRW, Antonov and Solomon have been the subject of patent lawsuits some involving Toyota. They involve manipulating power with two or more motors with a CVT planetary gear set. The idea is not new. Toyota in the 90's decided to refine it, produce it and sell it at a profit. It was difficult for them and risky. They are to be given credit for it. They are not the inventor of the system but I guess they have some patents for innovation. Making it operate smoothly, reliably and efficiently is the charm.

 

Thanks for the background. I am not surprised by this story. A similar story is William Edwards Deming and his Statistical Process Control SPC concept which was started in the US but ignored here, then optimized in Japan and finally embraced and fully implemented in the USA in the 90's, about 5 years after Japan had benefited greatly from its contribution to quality control.

 

As you say, Toyota deserves a lot of credit, for taking the risk of putting lots of development and manufacturing money into the idea, and you have to wonder about the detailed story of how and why TRW didn't see the potential of the concept. I know from experience that corporate patents cost corporations a lot of money to procure, so they should take the time to look at the merits/application of them very carefully. And Ford deserves credit for following a pattern that they have followed in the past, rather than play games try to engineer around the Toyota patents, or fight them in court, they treated Toyota with upfront professional respect, paid royalties and proceeded with the concept with Toyota's blessing.

[VonoreTn]

Don't put the traction motor into the equation. Just look at the ICE, MG1, and then the output of the ring gear. MG2 is just adding (or stealing) power to the output. The thing that makes it work so well is that MG1 is capable of turning at up to 6400 RPM - In either direction. That means a total of 12,800 RPM range on the sun gear.

 

That is one reason the "whrrr" or whistle that you sometimes hear on the FFH does not seem to match either the ICE RPM or the vehicle speed. Rather it is a function of the two. When you are accelerating the computer might actually start dropping the RPM of the ICE while the car is still increasing in speed. It can do this by decreasing the speed of MG1 thus changing the whirring sound you hear (seeming to move down in frequency). Neat stuff.

 

Jon

 

But MG2 is part of the system, it is active, so it must be included in the functional description. MG2 changing rpm is what gives MG1 the broad range of rpm. Yeah, I think I have noticed the reduction of ICE rpm while accelerating. Agreed, neat stuff, and repeating, my understanding is superficial at this point.

[lolder]

But MG2 is part of the system, it is active, so it must be included in the functional description. MG2 changing rpm is what gives MG1 the broad range of rpm. Yeah, I think I have noticed the reduction of ICE rpm while accelerating. Agreed, neat stuff, and repeating, my understanding is superficial at this point.

No, you understand it pretty well. A Ford engineer said about it once "it's all about thermal efficiency" of the ICE when running. They run the ICE at the lowest rpm, most advanced spark, leanest mixture and highest throttle plate opening that they can for any given horsepower requirement. Even though a lot is going on all the time, it's low wear type mechanical and electrical operation. No clutches, bands, brushes, torque converters, slip rings; just gears lubricated with oil. There is only resistance heat loss in the M/Gs, power electronics and HVB and a HVB charge/discharge cycle loss. Instead of the HVB you could store energy with flywheels, springs, hydraulic accumulators, etc. but they are unwieldy. The vehicle minutely manages the M/Gs at lightning speed with just phase angle and voltage changes.

[Oman]

In my quote above MG2 is the traction motor. I'll rephrase to traction motor. The reply was actually about understanding how you can use a single planetary to accomplish a very efficient transmission. The traction motor is a huge part of a completed hybrid but it doesn't have anything to do with the planetary and reduction motor being an efficient transmission.

 

As well MG2 doesn't alter the traction motor RPM. The traction motor is geared directly to the wheels. MG2 takes the narrow range of efficient ICE RPM and maps it to the larger wheel RPM. An electric motor already has a large RPM range.

 

 

Jon

 

 

But MG2 is part of the system, it is active, so it must be included in the functional description. MG2 changing rpm is what gives MG1 the broad range of rpm. Yeah, I think I have noticed the reduction of ICE rpm while accelerating. Agreed, neat stuff, and repeating, my understanding is superficial at this point.

[VonoreTn]

I thought MG2 is the traction motor. Are you using the model at the link here regarding the Prius system, which says that MG2 is the traction motor? I assume MG2 is geared directly to the front drive wheels.

 

Prius animation model

 

Is there an error in your first two sentences below, or am I really confused now? If your second sentence said transmission motor, it would make sense to me, although different from the link model.

 

In my quote above MG2 is the traction motor. I'll rephrase to traction motor. The reply was actually about understanding how you can use a single planetary to accomplish a very efficient transmission. The traction motor is a huge part of a completed hybrid but it doesn't have anything to do with the planetary and reduction motor being an efficient transmission.

 

As well MG2 doesn't alter the traction motor RPM. The traction motor is geared directly to the wheels. MG2 takes the narrow range of efficient ICE RPM and maps it to the larger wheel RPM. An electric motor already has a large RPM range.

 

 

Jon