Reducing Losses in the Rolling Chassis

[NeilBlanchard]

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?

[Laurentiu]

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

[NeilBlanchard]

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...

[dcb]

these guys don't flex much

[NeilBlanchard]

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

[RobertSmalls]

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:


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.

"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.

[NeilBlanchard]

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.

[user removed]

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

[Big Dave]

Ditching the torque converter would help a lot.

[Patrick]

Originally Posted by NeilBlanchard

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...

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