The myth of pulse and glide

I agree that we can improve without getting to far into the details of exactly how and why things work.

There is more than one way to do things ... not all are equal.

That does not mean that there are not benefits to be had from those details if we choose to get into them.

For 90+% of people ... I would not recommend getting into the technical side of things ... it just confuses most people ... but that doesn't mean that there is nothing out there to learn from those technical details.

Then of course there are just the tiny ~0.1% of people like me ... that just like knowing and learning about those details... I like learning about the details of who and why a solar cell works ... not that I will ever be designing some new type ... but I still like to learn those details... For me and the tiny few others like me ... it isn't enough to just know it makes electricity in sunlight.

Excellent ... and I 100% agree.... that is also a great place to start with P&G for most beginners to hone their skills.... then as they begin to see the results ... if they want to they can go out and learn more about the why it works and how it does what it does.

Thanks ... that is the kind of thing I had been hoping to see from the beginning :woot:

The data set is clearly missing important information... I would also take this further ...
what is the elevation changes and such of the route used? would also be another important piece ... not all routes respond equally to P&G... the route used could very well be biased against P&G.

Addressing the errors in what is presented... that's what I like to see.

Yeah not all engineers or scientists are any where near equal... I'll agree with that as well.

I was just trying to use it as an example that just because someone gets 100+MPG ... it does not make what they say correct... there are many many people out there that might get less MPG than me ... but who still know more than me about one ting or another ... and I can learn from them and fix errors I might be making.

 

As for not all routes responding equally, I completely agree. This is why I quite often take a different route when coming back from somewhere than the route I use when going somewhere. One example is when I take my wife to work: On the way there, my preferred route allows me to pulse up to 30-35 in 1/4 mile or less and glide for just over 3/4 mile. However, if I take this same route back, I would have to pulse P&G like this twice because it would be uphill. Because of this, I take a different route on the way back that allows me to 30-35 (usually 31 mph) for just over 1/4 mile but coast for ~3/4 mile. The beauty is that both routes (out and back) are the same distance.

 

One observation about technical people (IT, engineers, etc) - they often tend to be too wordy.

Speaking for myself at least, it's the fear that summarizing too much is the same as lying. I'm learning sometimes it's best to answer the question briefly and wait and see if someone really is interested in the details.

I have a different opinion on the graphs: it seems a lot more like "Shock and Awe" - I'm an Expert - end of argument.

 

It does not matter if you're a MIT Engineer to know P&G works, it's how you make P&G work. Go back to the basic SGII Instant MPG reading (not LOD) and find the key folks. The pulse is the key and the glide is the magic built in the transmission.

Don't hold traffic back! Just go with the flow and get there with the best MPG possible!

GaryG

 

Why Pulse and Glide works?

Engine efficiency is a function of compression. Not just the calculated mechanical compression but the real compression of the engine in the real world of driving.

Brake Specific Fuel Consumption graphs demonstrate where an engine is most efficient, but they may not clearly explain why any engine is efficient at certain speeds and loads.

Effective compression is the real compression at the instant when the mixture ignites and produces the multiple of the compression pressure and the work that makes the engine run. Effective compression can be easily read with a vacuum gauge. Highest gear, lowest engine speed and lowest measured vacuum, gives you highest effective compression.
Most automatics will downshift under these parameters so you have to modify P&G in an auto to avoid downshifting.

OK, don't go away yet:

Take any engine and put it on a Dyno and run it at 1600 RPM. Then using the hydraulic variable load capability of the Dyno place a 20 horsepower load on the engine, The Dyno measures fuel consumption at that load. Consider the amount of fuel consumption to be an amount that you assign a measurement of 1 unit.

Increase the load on the engine to 50 horsepower.

Now here is where it gets interesting, you only use half again as much fuel for 50 horsepower as you did for 20. To make this perfectly clear you use 1.5 units of fuel for 50 HP and 1 unit of fuel for 20 HP.

So you got 50 HP divided by 1.5 or 33.3 HP per unit of fuel, instead of 20 HP divided by 1 unit or 20 HP per unit of fuel.

Now you use the cheaper 50 per 1.5 units to accelerate your car up to the higher speed and turn off the engine and spend the extra power using the vehicle itself as an energy storage system.

Now I am pulsing and using more fuel overall during the pulse, but more than recovering that lost fuel during the glide, especially if I turn the engine off and use no fuel.

If I use 1.5 units and pulse for 1/3 rd the time but use no fuel during the glide, I have used 1.5/3 or .5 units of fuel versus 1 unit of fuel when not incorporating P&G.

That's a 100% improvement in fuel economy. By keeping average speeds lower the difference between constant engine speeds and P&G in overall fuel consumption becomes even greater up to about 400% if you were patient enough to pulse to 30 MPH and coast to a stop. The problem here is it will only work on deserted roads and with very patient drivers.

Now here is your trade off, as your speed increases the aero drag increases exponentially.
At higher speeds aero drag is 70% of your energy consumption. At higher speeds (constant without P&G) your engine efficiency increases as it has to sustain higher horsepower to overcome all the drag factors but especially aero.

This means that as average speed increases their is a law of diminishing returns for P&G.
Depending on your CD this speed may range from 55 MPH on up. It would be higher for a car like BASJOOS with very low CD and lower for an SUV.

There is another factor called sectional density. That is the weight you have behind the frontal area of your vehicle. Cars glide further with more passenger weight, but take more energy to get to the peak pulse speed. Small lightweight cars with more frontal area will slow down faster during the glide phase of P&G.

Now I could go on an try to describe the effects of reciprocation losses, pumping losses, transmission losses, and the myriad of other losses involved with the conversion of fuel energy to linear vehicle inertia, but at some point most of you would just get bored and your minds would wander off and comprehension would disappear.

I made a living explaining complicated technical problems to customers who had a broken car. I am not an educated (in the formal sense) engineer and I have tried to make the explanation understandable to most people who might be interested.

I know that if the manufacturers concentrated their energies on designing vehicles so they had the capability to self pulse and glide then every driver could improve their MPG. That is the secret to the future car, to move the effort to the system (car) and reduce the effort of the operator to obtain mileages many non interested parties would consider impossible.

regards
gary

 

I said that I was out of the thread, but I can't resist. That may be the problem we all have

When I worked for DOD I frequently provided TECHNICAL briefings to upper management. The tests of a good presentation were these:
1. Is it firmly grounded in the truth?
2. Introduction, body, summary, discussion. Tell um what you are gonna say, tell um, tell um what you said, answer questions.
3. Be economical in the use of words to guard the valuable time of your audience. Clear, non-repeititive, unembellished language. No strange buzz words or obscure abbreviations.
4. Good charts and graphs. Well defined axes and legends. No undefined graph entries. Liberal use of color if it truly differentiates difficult data.
5. Trust the intelligence of your audience.

From what I see here, many folks could stand to go to the DOD briefing school - no names mentioned.

 

Sad but true.

Sad because to me and the tiny minority like me ... that is the kind of detail discussion that I get the most interested in... and while that post was very well written ... it was just the tip of the ice-berg.

Even if the pulse is not directly more efficient ... the lowered amount of engine losses in the glide can to some degree still compensate for it... and can still give a net benefit.

But I guess the technical details like that ... as you wrote ... most people would just get bored ... and loose interest.

I think this is already happening little by little.

Synergy drive types of transmissions and CVTs are a great step forward in trying to keep the ICE operating as efficiently as possible as often as possible... Hybrid systems to recover some of the losses ... and turn off the engine sometimes when it isn't needed , etc...

As PHEV and REEV come to market they will be able to do even better.

I personally still wonder a bit about where the break even points are for different methods and designs ...

I mean a REEV like the Volt running a ICE at its peak efficiency can offer a nice helping hand to total vehicle net efficiency ... but by running an ICE to power BMS ... to charge a battery ... to discharge a battery ... to power a Motor controls... to Run a Motor .... there are allot of losses there in conversions in that complete cycle to get back to the Mechanical energy it started with.

On the other hand CVTs and Synergy drives and other types of transmissions can only do so much... to try and keep the ICE in a more efficient mode of operation ... and no matter how much they do ... there are varying loads and power needs that just complicate it even more.

I think the tiny bits ... will continue to come ... but for a long time yet to come ... the driver is still going to play a major / dominating role.

Now that is an excellent job of looking at the other details

You can always still work at improving your skills and such... but if you can find a different route that uses less gallons of fuel to drive than that can be a massive benefit ... and the increased skills can continue to help by stacking on top of that.

I know a few months ago I moved to shorten my commute... My commute is now ~1/4 the distance it was... yeah there will be a hit especially in the winter time with a increased % of my commute distance being with a cold engine and such... but the ~1/4 distance provides a massive benefit to reducing my gallons of gas used.... after all even 31MPG for 3 miles uses less fuel than 200 MPG for 20 Miles... and a 3 mile trip can also still benefit from 60 , 80 , or 100+ MPG...

So by all means look for those other details ... find the better routes ... it's all good

 

In other words, if you can't dazzle 'em with brilliance, baffle 'em with bulls***.

That technique sometimes works for persuading your boss to leave you alone to let you get work done or making others quit an argument, but other techniques work better to actually sway opinions.

+1 to Jim's outline.

 

Just a quick note, Ian -- the Volt is set up to power the motor directly from the generator attached to the engine when in charge sustaining mode. This cuts a good bit of inefficiency from the equation by skipping the battery.

 

Anyone ever hear that it's supposed to be impossible a bumblebee can fly?

Did scientists try to discredit the bumblebee or try to find out why they can fly?

 

Until they realized the Bumblebee is providing lift in both directions with his wings.

IamIam.

The combined effects of multiple transformations in the state of energy is something not easily understood, but it is similar to what happens in communication when multiple parties hear a story and try to repeat that same story.

The issue with hybrids, and the reason I like the hydraulic option, is it minimizes the transformations in the state of energy in regeneration. While the energy density of accumulators does not equal batteries in long term application, accumulators are perfect for short term high output power, and they have life expectancies measured in decades and are easily rebuild able.

In another thread a member mentioned a electric-hydraulic hybrid, which is an option being considered. It may be that when battery technology gets to a point where it is affordable and reliable, the electric-hydraulic option will be the winner, but we are not there yet and it may be a while longer before we get there.

A Pev with hydraulic launch assist would be more capable than a PEV alone. The launch assist would be an energy damper for high load acceleration and high regenerative braking. When I read about people hypermiling an early Insight and avoiding regeneration or assist at all costs to maximize mileage, I can only think why have the battery components in the first place? They definitely add weight and considerable complexity to the system while from the practical experience of absolute fuel economy they are useless.

PEV vehicles at this time still have serious energy density deficiencies compared to gasoline or diesel fuel, but hydraulic launch assist would work with either system for two purposes. First is regeneration of over 80% of braking losses. Second is to allow the operator, or the vehicle itself to incorporate Pulse and Glide while maintaining a constant speed.

This is done by pulsing the accumulator with the cheaper energy consumption of using the engine only at its highest BFSC point and using any surplus to charge the accumulator. That same energy is then applied to compensate for the losses that cumulatively reduce vehicle speed in the normal glide phase. There are some losses in the charging of the accumulator, but with accumulators at 96-99% efficiency and pumps at 93+% efficiency the losses are offset (at least to some point) by the losses in encountering higher aero drag in the pulse phase of the current technique.

This is why I believe a power train platform that incorporates short term high energy density storage can be utilized in any vehicle regardless of whether it is powered by IC or electricity.

Eventually that philosophy will be incorporated into vehicles. The technology is available right now, and the Hydraulic option should be better understood and given a chance to compete with the other options.

It should not be exclusive when it comes to development and many examples show that in real world situations the engine on time is around 12 %. When I tested P&G in my brothers 90 Honda Civic, I found that travelling 9 miles in 18 minutes, required the engine to run 4 minutes and 15 seconds, a duty cycle of 255/1080 minutes. That worked out to about 25%.

The percentage is almost a direct function of the average vehicle speed, which for me was 30 MPH. Lower speeds would reduce the engine on time, while higher speeds would increase that same time.

The key is to find a way to disconnect the IC engine from the powertrain, while recovering energy efficiently when deceleration is required and using that same energy to reaccelerate and provide engine P&G without vehicle P&G.

regards
gary

 

A seamless transition from drive to neutral creating a pulse and glide effect while maintaining not a constant velocity, but speeds + or - 1-2mph of target speed.

Re-engaging the motor using the cam to detect positioning and firing on the second or third rev to minimize losses incurred due to unintended engine braking.

A hydraulic launch assist is an idea I've toyed with, however not in exactly the same fashion. The launch assist was spring loaded in my vision.

 

I'm aware that we have reported Ford considering hydraulic hybrids for the F150 and UPS (UPS Takes the Lead on Hydraulic Hybrids) actually has delivery vehicles using this.

If perfected, it bypasses battery and current concerns.

 

I’m coming in late to this discussion.

My job is to read/write technical software documents and make sure the programs or corrections to the programs will meet our business requirements. I also perform QA in test environments and explain the documents and results to management. There is a huge difference between meetings with developers and management! I can have 5 pages of a document describing something that I can explain to management in one sentence.

I would agree that engineers are a bit long winded, explaining things in minute detail when a much simpler explanation would suffice. But, that is the way it is. They want to make sure you completely understand the information they are presenting.

Funny stories and to make a point about the above. I wrote specs for a report that pulls data from our manager bonus program. I do not have the document for the exact wording but I included pages will be numbered in the format “page 1 of 1” in the upper right hand corner of each page including the cover page. First draft I looked at in test had “page 1 of 1” in the upper right hand corner on all pages. I did not specify that the numbers had to be incremental according to the number of pages on the report.

Another time we added download to spreadsheet functionality for the sales force. I included everything I thought we needed. First draft in test….. It downloaded but everything was converted as text. I did not specify that we required all numeric fields be converted as numeric and respond to mathematic functions.

For P&G working. For me it is but not with the expected results. It will take me time to discover what the best acceleration rates are and the best deltas are for my conditions. When I find these I will gladly share for others to benefit from… In layman’s terms of course.

 

Yup and it was a good plan.
And it is a nice system that will benefit a fair number of people.


just my own 2 bits...

Even then... there are significant losses.

Gasoline to ICE to get Mechanical power... 1 Unit output.
Mechanical power to electrical power generator ~0.95 Units output.
( if they get ~95% efficiency )
Control electronics ~0.90 Units output.
( if they get ~95% efficiency )
Electrical power back to mechanical power ~0.85 Units output.
( if they get ~95% efficiency )

Even if they can get ~95% efficiency at each of those steps ... they still lose ~15% of the mechanical power the ICE produced from the gasoline it consumed.

That's the good option where they skip the battery cycle losses... which would add in a second set of control electronics when coming out of the battery... and also the battery losses itself... which even if they are able to get ~95% efficiency in the second set of control electronics and the battery cycle ... that would reduce the net output to ~0.76 Units....

so yeah ... skipping the battery step saves significant inefficiencies ... but the system itself still has efficiency vampires that are less easily removed.

The saving grace for the system is that the efficiency change of the electric motor does not change as much under load , RPM , temperature , etc... variations as a ICE does... it does fluctuate ... just not as much as an ICE does.

Under some conditions this is a net benefit when compared to the losses that happen when the ICE is pulled out of it's preferred efficiency operating conditions.

But with very cleaver transmissions like the Synergy drive ... and others ... The transmission can be used to some degree to keep the ICE closer to it's more efficient operating conditions a greater % of the time.

For instance while cruising on a flat level road ... where the mechanical power output from the ICE in a good / efficient zone ... the ~15% loss in the conversion steps is just wasted energy.

So I still wonder where the break even points / conditions are... and I would also like to eventually get more data on the performance curves of the electronics ... the batteries ... the Electric motor ... the Electric Generator ... the ICE ...etc... some details have begun to come out... but allot is yet to be seen / revealed.

Yeah to the detail people who kept researching it to find out how and why.

That is a good analogy.... I've often struggled myself to try and explain it to non-detail / non-technical people.

Just today a Co-Worker told me I should use an alternator on my E-Bike to get 'free energy'... He meant well ... but he just didn't grasp the details that made his plan not work... I tried to explain it to him ... but as you posted before ... when detail / technical people try to explain something to a non-detail / non-technical person ... the other person very often just looses interest ... so it ends up being an entirely different type of communication skills to communicate like that effectively.

The hydraulic systems I've seen have been a nice alternative ... and as you touched on above... they do have some nice benefits.

I still wonder about some type of advanced Flywheel and transmission systems... Most ICE engines already use a fly wheel as a very efficient method of load leveling short pulses ... and the new transmissions have been getting better and better ... Transmission efficiencies are already very good... and it is a whole different set of problems if you try and run without a transmission at all.... so there is likely to be a transmission anyway.

Of course we will have to wait and see how the research goes on all the many different options to see how they manage to over come the complications / issues involved with each approach.

Still... with so many different approaches being explored ... it is an exciting time to watch as each makes improvements one at a time... tiny little baby steps forward each time... not always in the same way ... one might get a bit better power pulse ... another might get better at higher Voltages ... another might get better at weight ... another might get better at manufacturing costs... another might make improvements in the end of life effect of the parts... etc...etc... Exciting stuff :woot:

I think like so many other things ... it ends up depending on the specifics of the application ... which will greatly effect how I might determine what is 'affordable' or 'reliable'... as both are kind of subjective.

For instance I'm at over 9 years with my Original NiMH battery pack in my 2000 Insight... the few Rav-4EV's that I know of ... are also still on their original battery packs for even longer... I'd say that these ~10 year old technology versions of NiMH batteries have been showing excellent reliability ... but that always depends on the specifics of the application / conditions ... in other applications / conditions , they might not fair as well.

Of course affordable is also subject to personal preferences and the specifics of the application / conditions ...

I've seen EVs and such where ....
PbA batteries can be bought as low as ~$150/kwh.
NiMH 12Ah 'D' cells can be had for ~$520/kwh.
LiFePO4 40Ah Cells can be bought as low as ~$640/kwh.

So , depending on the application / conditions ... batteries either could already have been reliable and affordable enough for many years already ... or they can still have a long way to go.

I think it depends... under some conditions ... they are just dead weight.

But with no IMA / HEV system at all... you do give up things that help ones fuel economy... Auto-Stop, Regen Braking ... less load on the ICE to get that same pulse of power ... etc... etc.

But there again... under many conditions the OEM system can be just extra weight ... especially for allot of Highway driving ... when trying to make use of Lean Burn... etc... etc...

where it breaks even... where it is a hindrance ... where its a benefit ... is all in the details , specifics , and conditions... which we already wrote ... most people just don't care about.

People want that pulse of power to accelerate, pass, etc ... Allot of vehicle ICEs are over powered in order to give the driver those power pulses they want... the IMA system even for it's losses ... is an alternative approach to giving those few & often infrequent power pulses the consumer wants , without over sizing the ICE to do it.

Even putting that aside ... I think that the HEVs have been a good thing ... they have put funding and focus more into better vehicle / mobile application batteries ... control electronics ... Motors ....etc...

And good or bad ... new technology itself is a selling feature ... in and of itself ... even if it doesn't effectively do anything... it still has some retail value, just in the perception of being 'more advanced'.

I can see where that could be a benefit.

Wouldn't a flywheel system have better efficiencies ... not having to have to convert it out of mechanical power / energy at all??? Although there again Flywheels are a long way off to get the energy density needed... without having a significant weight penalty.... and many other issues as well.

I agree.... and I look forward to continuing to read up on the details as they come out bit by tiny bit.

Or at least remove the power losses that result from a connected ICE.

But disconnecting it does a very effective job of that.

 

Quite agreed on the Volt tech, Ian... but it really shines for someone like me who would very seldom use the gas engine.

Of course, then it becomes dead weight -- which is why I'm more inclined to get a full EV and then just pull a generator on a trailer when and if I need more range.

 

Only if it's a small, 2 mode (high efficiency charge and max recharge) turbo-diesel with a 5 or 10 gallon tank for fuel. Please note that if this idea has not been patented, I am placing it as prior art in the public domain (as of the time of this post).

 

In wheel Infinitely Variable Transmissions with accumulators allow the power train to be completely separated from the engine. Accelerating from 0-60 (or pick your speed) is solely accomplished by the power train, irrelevant of engine operation. The threshold of efficiency is 80%. By moving the drive function to the wheels themselves you reduce the RPM eliminate any connection other than supply and return conduits for fluid.

Now you system is Wheel-Accumulator-Wheel. You can have a multiple of acceleration-deceleration events with no engine operation, while you can also use the accumulator to accomplish start-stop of the engine.

When you dedicate engine operation to only accomplish replenishment of accumulator pressure, you can also eliminate the necessity for any throttle control of the engine itself, and focus all function on a narrow range of RPM and a specific range of load, which spells high BSFC operation and only the best efficiency.

As mentioned in the previous response talking about the Volt applying energy directly to the drive, this system can apply engine power directly to the wheels, but only when it is also applying power to the accumulator. Choose your pathway based on efficiency alone.

Most hydraulic pumps suffer significant efficiency losses at higher speeds above 1000+ RPM. You match tire-wheel diameter to the best pump efficiency range to minimize losses.

If my Insight had only a small accumulator and a launch assist rear axle, returning 85% of the inertia lost in braking, it would weigh no more than it does with the battery configuration.

But here lies the real improvement. At constant speeds you can also P&G the engine to charge the accumulator and bleed the accumulator power to the IVT to maintain 45 MPH while cycling the engine at best BSFC. No electric hybrid can do that and it's doubtful that they will ever get the system to overcome the totality of losses to the point where it will be possibly electrically.

My Insight has a CVT, which provides an infinite range of "ratios" but has fixed upper and lower ratio limits. IVTs suffer from no such limitations. In wheel drives can be selectively disconnected to provide better overall efficiency by using 2 wheel drive, when 4 wheel traction is not necessary, while retaining the ability to regenerate at all 4 wheels to the limit of the wheels traction.

Winding up the hydraulic "spring" gives you back most of the energy normally lost or recovered at poor levels of efficiency. I am not trying to argue with you IamIam, but I think your 95% figures are optimistic. Lets say 90%, but 6 transformations, and you are at 53.14%.

90% with 2 transformations gives you 81%, so you can see why wheel to accumulator to wheel has a distinct advantage over electric regeneration. The gap in efficiencies may be impossible to close (emphasis may).

If you can get to 95% (already there with an accumulator) with accumulator and motor, you are at 90.25% hydraulically and the electric option has an even greater gap to close.

Now combine that understanding with the additional advantage of the hydraulic system is the ELIMINATION of the conventional power train and you offset the cost of the hydraulics by eliminating the conventional power train, a significant reduction in overall vehicle complexity, which could be used to cover the additional weight and cost of battery storage.

It may well become obvious to many that the only way to have an effective range in a vehicle, where the stored energy source is a battery, is to use a hydraulic IVT power train and surge storage.

Now you can have a local PEV with an extended range IC power module that you can install for trips and remove for local use. This eliminates the necessity for two vehicles for each purpose.

I believe the technology is already here. My Insight demonstrates the principles to me every day, but if I could convert it to hydraulic storage, while eliminating the battery, electric, motor and the rest of the power train, by substituting 4 in wheel IVTs it would weight the same or less than it does not and have blistering acceleration.

If you only changed the rear axle to launch assist, you would see a benefit with no weight penalty, but I consider that a transitional phase in development of the eventual series hydraulic hybrid.

Please do not think of this point of view as excluding the electric storage option as an eventual replacement for IC and liquid fuel. I think at some point in time we will get there.
Parallel development will get us a large reduction in hydrocarbon use for transportation now, and provide competitive incentive for all involved in future development to place their best cards on the table quickly.

On vacation for a couple of days here, back tomorrow evening.

regards
gary

 

Craig, I have to confess I got the idea a couple of years back from a resourceful RAV4-EV driver.

Here's a question MAYBE you can answer for me. Any chance the upcoming Focus EV won't have an immobilizing function when plugged in? 100mi AER would work fine for me when it comes to normal driving but if it would run with a generator plugged in I could go anywhere in it (for the 2 or 3 times a year I actually want to exceed 100mi on a single trip).

I'd settle for a special outlet in the trunk for such a function... just so long as it is possible without tearing into the wiring/programming!

 

I would gladly settle for an EV Ranger (or similar) with a 75 mile range and the ability to drop a generator in the bed for longer trips.