Reducing Losses in the Rolling Chassis
 

While power plant efficiency is a very important factor to the overall vehicle's efficiency, there are lots of ways to improve the rolling chassis, as well.

Rolling efficiency is the most basic function of any vehicle; however it may be powered. This involves:

* Tires, wheels, wheel bearings, suspension, wheel alignment (loaded and in motion).

* Ride height and attitude -- both of these are critical to good aerodynamic drag, and we should not leave them to chance.

* All aspects of aerodynamics: overall shape and size, specific details, ventilation of the passenger compartment, motor/drivetrain cooling/temperature control. By using good passive air management, we can both improve the air flow around and through the vehicle; and avoid needing a power input to actively solve these requirements.

* Weight and friction of all moving parts (if you can avoid power steering and power brakes, this reduces the losses of operating the vehicle).

+ Temperature stability affects a lot of things: the people, and the drivetrain in particular. Learning from buildings, we should use insulation and low-e glazing to help stabilize the temperatures.

+ Braking should be regenerative: either electrical whenever possible, or, we should use hydraulic motors and a small accumulator; instead of friction brakes which produce waste heat.

+ Especially if the brakes are regenerative hydraulic, then the suspension should also be regenerative; and use the shock pistons to also pressurize the accumulator. If possible, the entire suspension springing should be hydraulic, I think. Because flexing springs also produce waste heat. Alternatively, the suspension could be electromagnetic.

Can you add to this list of improvements, please?

I like what Michelin is doing with their "Active Wheel" system

I agree that airless tires are what we need -- and I would like to see this go even farther: to reduce rolling resistance to an absolute minimum, and to make even better use of the regenerative suspension I mentioned above -- I think the tires should have virtually no flex! This "wins" in two ways...

these guys don't flex much
http://www.ambient-light-photography...in%20wheel.jpg

Exactly! Add a rubber tread, and we'd be good to go! Bring it on...

This seems like a great place to post the road load equation:

Road load = (rolling resistance) + (aero drag) + (intertal and gravitational loads)

F = m*g*Crr*V + .5*rho*CdA*V² + m*(g*dZ/dt+dV/dt)




Although many generalizations are available, there are no absolutes about the relative size of each term. I'd encourage you to measure each term for your driving style and set your priorities accordingly.

I will argue that the importance of reducing mass is underestimated. Hypermilers underestimate it because energy that you put in to the car during acceleration and ascent is stored as potential energy that is later released. However, if you brake, you've wasted that energy. Regen only recovers a certain percentage, though it's better than the 0% you get back without regen.

Mass begets mass: Adding a 50kg accessory to the car will require the addition of approximately 50kg of additional structure and propulsion systems. In the case of a gas engine, the larger displacement required as a result of additional mass also results in cruising at a higher BSFC.

I could write a book on the subject of automotive efficiency, but that's been done before, so I'll limit myself to another paragraph.

CdA. It is not due to a lack of knowledge about the benefits of boat-tailing, nor a lack of skill on the part of the responsible parties, that we so seldom see production cars shaped like a streamlined body. It is because aerodynamics is not the primary determinant of the car's basic shape, or even of many of the details. Customers desire a prominent grille, muscular fenders, open wheel wells, and an identifiable sedan or wagon. In the case where they allow a Priusian fastback, they desire a very usable cargo area with easy access. The Insight's cargo area is very small, and not tall enough to be very useful. This helps explain why this $20k, 60+MPG rated vehicle never sold in large quantities.

What we EcoModders are doing is striking a different balance between curb appeal, comfort, utility, versatility, cost, and efficiency. If you're willing to throw away EVERYTHING expect efficiency, you can build a 200+mpg vehicle.

A vehicle with relatively high road load:
http://ecomodder.com/blog/wp-content...treamliner.jpg

A vehicle with lower road load, but less versatility. You can get extremely low CRR bicycle tires, and I'd love to see an Edison2 that rolls on four of them. The safety aspect might be lacking, so drive carefully.
http://www.adventuresofgreg.com/images/frame.jpg
"Critical Power human powered vehicle is one of the most energy efficient vehicles in the world. With a drag coefficient of .25 (CdA sq ft), wheel rolling resistance of .0050 (Crr) and weight of 70 pounds..."

So there's two examples of very low CdA combined with very low mass.

another example
 

Thanks for that, Matt. Another example is C. Michael Lewis' Electrathon vehicle we saw in Watkins Glen, NY. He traveled 62 miles and used 938wH, which is 2,249MPGe or ~15.13Wh/mile.

I agree that weight is very important, though I think it is more important to achieve higher efficiency on each of four things (in approximate order of importance):

Drivetrain efficiency.
Aerodynamic drag.
Weight.
Rolling efficiency.

The hydraulic hybrid power train was 78% efficient at recovering braking energy. This was a quote from Ryan Waddington at Next Energy in Detroit when I went there for a conference with Ricardo in 2006.

I had transitioned from an engine configuration to a direct in wheel drive over the summer of 2006 and Ricardo told me they were not prepared to consider the drive configuration.

Ryan suggested the best way to rapidly implement the design would be to configure it as a launch assist rear axle in a FWD car. With run flat tires or even other airless designs not capable of going flat with low RR, you could use the spare tire well as a location point for the accumulator, with it shielded with sheet metal in case of a catastrophic failure in an accident.

This would allow a currently produced vehicle to be upgraded to a launch assist option without any major redesign, or siginifiant additional manufacturing cost. No payback time period, immediate mileage benefit.

This would allow regenerative braking, but there is a critical additional benefit.

As long as your in wheel drives are truly Infinitely Variable Transmissions, you could configure the engine to go into a phase of operation where it only operated at highest BSFC while replenishing fluid pressure to the accumulator, when cruising at constant speeds with fairly light overall energy requirements. I would guess the threshold would be somewhere around 60 MPH, but if RR aero and other parasitic drag losses could be reduced overall then the 60 MPH figure would increase.

It is CRITICAL that you objectively consider this most crucial component of the system.

Understand a graph of energy demands with the 0 requirement line, where you have positive energy requirements above the line, and unnecessary losses below the line. The graph bounces all over the place, while the system I am proposing would eliminate all below the line losses and the positive requirement peaks would also disappear.

Cycling the engine only at highest BSGC would produce periods of 0 (on the line) no energy requirement, with periods of engine operation only at highest efficiency.

I have probably linked the INNAS HH BMW here several times previously, but they doubled the overall mileage using this exact operational tactic, so the benefit is documented by their efforts as well as the efforts of others.

I do NOT discount or have any reason to not consider the same power train configuration with pressure replenishment accomplished by simple applying battery power directly to an electric motor to pump hydraulic pressure to the accumulator. This would even possibly eliminate the necessity of any module to convert the battery energy to AC for the motor itself (cost $1900 for my insight)

I would imagine a Nissan leaf with a simple launch assist rear axle could possibly increase its range by 50% which would make it much more practical for many people who need that additional range.

The prototype is in the process of being designed to be built, and the motorcycle I am using to build a complete vehicle will weigh about half of the weight of its original configuration. Hopefully in a few months it will be operational. If it works as I think it will, it will refute any claims of HH being impractical due to weight penalties. INNAS has already proven that there is no weight penalty, but their design uses fixed displacement pumps which are less efficient, since fluid is constantly moving through the in wheel pump-drives.

My design would not need the transformers used in the INNAS configuration since the variable and reversible displacement in each in wheel drive allows infinite adjustment of the power applied to each wheel individually. The configuration could even be used to produce a vehicle that could corner unbelievably by apply different levels of power to each wheel completely independently of the other wheels.

regards
Mech

Ditching the torque converter would help a lot.

I'm not sure that would help:

The pneumatic tire also has the more important effect of vastly reducing rolling resistance compared to a solid tire. Because the internal air pressure acts in all directions, a pneumatic tire is able to "absorb" bumps in the road as it rolls over them without experiencing a reaction force opposite to the direction of travel, as is the case with a solid (or foam-filled) tire. The difference between the rolling resistance of a pneumatic and solid tire is easily felt when propelling wheelchairs or baby buggies fitted with either type so long as the terrain has a significant roughness in relation to the wheel diameter.

Tire - Wikipedia, the free encyclopedia

Thanks Patrick -- I think the key phrase is "so long as the terrain has a significant roughness in relation to the wheel diameter"

Roads are typically fairly smooth, and other than potholes, they do not have "a significant roughness in relation to the wheel diameter". Nothing a little experimentation wouldn't help determine.

Yeah, but if you cut off the flanges, they corner like cr*p :-(

Err... And where do YOU live? Around here, a good many roads (the major paved ones, not dirt or paved side roads) are pretty darned rough. I can & do see significant differences in real-time mpg on different stretches of (level) road. And of course there's I-80 over the Sierra: the last time I drove that, I was worrying about high-centering on the ruts that traffic had worn into the concrete.

I'm in the Not Ga Ga Over Solid Tires camp.

I think bicycles offer the perfect illustration why. For decades my ride was a Fuji road bike with 27 x 1 tires at 105 psi. I still have it but now I much prefer to hop on my full-suspension mountain bike with 26 x I think 2" slicks at 65 psi- and that's just for going around town 100% on pavement. The comfort factor in favor of the MTB is practically beyond debate, but I've found the r.r. on the much heavier bike with the lower pressure fatties to be very favorably comparable. So I'm not beat up OR worn out when I get there.

You know, once upon a time solid tires were the standard and pneumatics shoved em out of the market partly because of the rolling resistance improvement- as noted in a previous post.

I suppose if a vehicle rides like crap it would save gas... cuz nobody would want to use it unless it was absolutely necessary.

That said, I could totally get behind a compliant yet airless tire system, if only to address my impression that only, oh, 10% of the motoring public knows what a pressure gauge and air hose are for. :rolleyes:

well, there's solid tires and there's airless designs of tires (a.k.a. "tweels"), totally different things.
We have to look out for these in the future when they manage to outcome some of their drawbacks (such as vibration &noise)
http://declubz.com/blog/wp-content/u...less-tires.jpghttp://www.toxel.com/wp-content/uplo...07/tweel03.jpghttp://www.xensory.com/blogs/transpo...next/tweel.jpg

Video

I think you'll find the airless tires has more mass than the pnuematic tires - which is probably why you haven't heard much from the vehicle manufacturers on this subject.

I had the same thoughts, ouch. New Mexico is NOT known for smooth roads, and those are the ones that are paved.

Are they planning on sealing up the sides of those tires? I could just imagine getting 5lbs of mud stuck into the side throwing them way out of ballance.

You of course, would have to tune the suspension to work with solid/airless tires. And if you did have regenerative shock absorbers, the solid tires would "pass along" most of the energy to the shocks; rather than the tire heating up.

The "TWEELS" are all made to work just like pneumatic tires -- and not only with dirt/mud/snow build up in those open cells -- the aero drag from these is pretty horrible, too.

I'm not going to say it cant be done, because suspension systems have advanced so far as it is, but running a solid/airless tire makes it harder to get a smooth comfortable ride that will be necessary for the masses to accept them as an option. On top of that the transition to motors in the hubs is going to increase the unsprung weight putting even more demand on the suspension to smooth things out.

I do not care much for hub motors just think what happens when you hit that big pot hole that looks like a puddle and you pop your tire and bend the rim. Time for a new motor.

The tweel is a neat concept and could be a viable choice if they fix the high speed vibration, noise, and heat issue. Probably could be fixed by sealing the sides and placing it under a slight vacuum.

Has anyone tried reducing the weight of a vehicle by sealing the frame of the car and filling it with helium? I know that it sounds ridiculous but if it is not under pressure the air gap in the frame will be lighter and since it is a noble gas it will not react with the metal and cannot ignite.

Re: Tweels and such: I'm certain the engineers did not overlook the pitfalls of the open architecture. It's just that a marketing presentation for the concept would fall flat (pun!!! :rolleyes: ) if sidewall membranes were installed and the thing looked just like a conventional tire.

I think airless tires have one MAJOR drawback:

People.

A pneumatic tire can only be neglected until it pops, and then the user MUST replace it.

Airless tires would need some way of becoming absolutely undriveable when worn past safe margins, or you know a good 20% of the people on the road would just keep blindly driving on them 'till they're 10" diameter and the brake disc was contacting the road.

What I want to know is where the F are our peristaltic self inflating tires? Been hearing about them forever but when I visit the tire store they just aren't there.

"Lack of tire pressure maintainence" i.e. people, is the biggest problem with pneumatic tires, and the best reason to install twheels. I'll stick with my LRR pneumatics for the forseeable future, of course.

Once the twheel runs out of rubber, and the steel meets the road, it will be sufficiently undrivable for lack of traction that the people you refer to will have to apply a can of spray-on undercoating, or screw scraps of old tire to their bare twheel.

There's not enough volume there to make it worthwhile. You need hundreds of thousands of cubic feet.

Someone did make a bicycle frame of tubing about the gauge and size of a soda can. Air pressure was used to prevent buckling, and it did come out somewhat lighter. Unfortunately, the wind resistance issue was more important.

I saw a picture of an Atlas rocket in a museum. Apparently, the upper fuel tank is so thin-walled that it too needs pressure to support the payload. Unfortunately, the museum air supply had failed, and the rocket looked, shall we say, unable to penetrate. :-)

Other issues that relate to rolling efficiency:

Wheel Alignment while rolling straight and while turning.

Dragging/free spinning brakes

Wheel bearings -- wear and rolling drag.