What makes cars fuel efficient?
Cars back in the day were much more fuel efficient than todays cars.
For example. The 1992 - 1995 Civic VX gets from 42 - 60 MPG The Geo Metro Xfi gets from 40 - 65 MPG From my observations what makes these vehicles so fuel efficient? 1) Lower HP 2) Light Weight Now comparing to Compact cars today why can't we have gas efficient cars like these without the battery pack? I think safety regulations play a big deal in part of this because there are certain guidelines to how much a vehicle has to weigh and there is a min. HP it has to have. Even the new Chevy Aveo gets 24-34 MPG which I think its not that great when you factor it's 1.6liter engine and it's weight of 2300lbs. It should be getting at least 30 city and 40 HWY Is there anyway to modify the Aveo's transmission so that it gets this kind of MPG? |
I also blame whiny barsteward auto hacks and reviewers who complain about 0-60 times being "poor" at 9 seconds.... back in the day anything doing better than 15 was a sports model. Least powerful motor you can buy in a compact these days? 105 HP I think... which was the most powerful motor you could get in a Chrysler minivan back in 1985...
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i own a civic VX and I have to say its not that bad. I get good FE and not have to sacrifice performance. I also had the geo metro and I have to say that its handling was pretty bad but its performance was okay to get by with.
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less efficient: more cams and valves. more moving parts, more friction parts (more valves=more pressure against cam, more resistance as they have to climb the lobes, more pressure on bearings). Emissions equipment and tuning, both noise and gaseous.
that's why the dinosaur of an engine in my truck gets 25 mpg mixed. 4 speed manual (no OD), 2.5l (big engine for this forum), and a computer that makes a pocket calculator feel good but OHV and a gear-driven cam. that and the springs are so light the valves float over 5k or so I've heard. hell it got 24 mpg going 65mph carrying 1000lbs |
It's a conspiracy I tell you.
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Was just looking up my drag coefficient (.36) and saw lots of bad reviews saying my Cavalier didn't have enough cam and valve stuff and only 115HP.I didn't see any complaint about the high drag or low EPA estimated MPG's.
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Theoretically, when you have one cam driving intakes, and one cam driving exhausts, you can have them turning half the speed with shallower ramped lobes. This means both that friction is reduced, because it increases with the square of RPM, so two 1500 RPM camshafts cause less frictional drag than one 3000 RPM camshaft at the same motor speed, additionally, because of the shallower ramps, I believe less powerful springs are required to keep the valve on profile and stop it skipping or floating, so there's less lossage there too.... however, they only get into premium engines that are tuned more for power because higher parts count means higher production and assembly costs, so it's not immediately obvious that twin cams=higher efficiency.
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I wouldn't call them effecient.
They waste most of the energy they consume. Hypermiling demonstrates this perfectly. To be effecient they need to be designed to hypermile naturally, without the driver having to be distracted from staying alive. Every act it takes to hypermile could be programmed to perform automatically, which makes it a practical solution immediately. The next step is to make it mandatory that every vehicle have a regenerative capacity so there is no need to use friction brakes. It's called a launch assist axle. Then they need to be able to shut off and restart the engine rapidly with minimum fuss, to eliminate the totally wasted fuel consumed at idle. Next you have to disconnect the engine from the accelerator pedal, by using the transmission for acceleration with the engine and some form of short term high output storage, enough for one acceleration cycle. I like flywheels or hydraulic storage for this becasue both systems are reaching the threshold of efficiency to make them the best system for great acceleration combined with the engine if necessary. They will also be virtually maintenance free with 500K life expectancies, and actually take about 600 fewer parts per vehicle to build. Take a 1500 pound vehicle with a 1 liter turbocharged HCCI multifuel engine, connect it to an infinitely variable drivetrain with capacitive storage and you have the ingredients to make a vehicle that can maintain any speed while the engine does exactly the same thing as an engine off coast in hypermiling but the storage and transmission allow a constant vehicle speed. regards gary |
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As far as inefficiency, I'd say size is one factor but the engine is your biggest culprit. That 1.6 in the Aveo we actually ran some testing on yesterday, that poor little engine is so gutless down low I'm suprised it gets 24MPG driving around town as it is, probably the low displacement. It's the first car I've seen we had to redline to make it up a couple of the acceleration ramps on our fuel economy test. Engine inefficiencies is one of the things I hope to address when I start working R&D with an automaker (crossing fingers). |
it's a 2.2L, I don't know what OHV is. It's got 2200 SFI on the injector cover.I was relieved to find I have a timing chain rather than a belt at 85K miles.
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As opposed to OHC = OverHead Camshaft = cam directly actuates valves. Wikipedia is your friend. |
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People think they want power but they don't realize you don't need much. In Europe small cars can come with 1.2 liter engines. In the US, if you want a vw rabbit, you get a 2.5l 5 cylinder. Isn't this overkill? |
horse power is always peek horse power and that peek is around 5,500 - 6,000 rpm on most civic engines, the peek torque on the other hand ranges between 3,000-4,500rpm, the cars that get better mileage tend to have better torque and at lower engine speeds like the crx hf had peek torque at around 2,500rpm and because of that feels like a very powerful car even tho the peek horse power was around 60hp.
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Yeah, you know that made my brain itch when I typed it, read that somewhere recently, hadn't thought about it carefully. Maybe that's what it was, the reduced mass, due to driving pairs of valves off one lobe and needing less leverage or something.
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chevette engine specs:(1.6L all iron everything) bore and stroke: 3.228 x 2.980 82.0 x 75.7 mm compression ratio: 8.5:1 net HP/@rpm: 70 @ 5200 max torque@rpm: 82 @ 2400 i belive 0-60 was in the 17 second range |
"From my observations what makes these vehicles so fuel efficient? 1) Lower HP"
This shouldn't be oversimplified. For example, compare the VX and CX ('92-'95). The VX has 31% more power, and still gets 13% better mpg. Why? Because the CX was built to be cheap to buy, and the VX was built to use less gas. The VX has a bunch of subtle tricks to boost FE, like roller cam followers to reduce engine friction. A good technical listing of various VX FE ingredients is in this pdf. "i own a civic VX and I have to say its not that bad." The VX has 18% more torque (and the same weight) as the Fiat 124 Spyder I used to drive. That was considered a sports car. What's happened is that our expectations have changed. Trouble is, we can't really afford our new expectations. |
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One more thing. Someone mentioned drag. This is another problem, ESPECIALLY with small cars (which tend to be MUCH less sleek these days than larger offerings). If you look at a 15-20 year old small car vs a new one, the new one is guaranteed to be taller and chunkier than an offering from the late 1980s or early 1990s. Perhaps the extreme example of this is the CRX, which was known for its GREAT mileage (especially in HF form). But even a VX looks sleek and aerodynamic compared to the overly tall small cars you see today. THIS is probably a big reason why small cars are just not very economical these days. And, because small cars tend to be MUCH less sleek these days than larger offerings, this is probably also a major reason why so many small cars just can't beat the fuel economy numbers of (much sleeker) midsized sedans by much of a margin these days. |
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"WEIGHT is a bigger problem than HP"
I agree that weight is very important. "Although HP has skyrocketed, it has really not outpaced weight by very much over the years." I don't think that's true. I think our standards have shifted. "170HP sounds like alot for a small car.... But a 3000 pound car needs this kind of HP just to be able to accelerate somewhat decently." Here's an example of what I'm talking about. The Chevy Impala was (and still is) one of the best-selling cars in the US. Let's pick the 1980 model, just for the heck of it. That car weighed 3,344-3,924 lbs. The base engine had 115 hp. The optional engines had 120-155 hp. Assuming the lightest Impala (3344 lbs) and the biggest engine (155 hp), that's 21.6 lbs/hp (and of course that's an overly generous assumption). 3000 lbs with 170 hp is 17.6 lbs/hp. That's what you're claiming is needed. But in 1980 lots of American buyers were willing to accept 21.6 lbs/hp, or something even worse than that. A 2008 Impala weighs 3555 lbs, and has 211 hp. That's 16.8 lbs/hp. So the car weighs about the same as it did in 1980, but the stock engine is now 36% bigger (in hp) than the biggest optional engine that was offered in 1980. Here's another interesting comparison. A stock 1980 Corvette had a 0-60 time of 7.1-7.7 seconds. The 2006 Impala has a 0-60 time of 5.7-8.4 sec. So the family sedan now has performance comparable to the 1980 Corvette. "I think that performance/acceleration is not really the issue." I've explained why I don't really agree. We have a problem because cars have gotten heavier, but we also have a problem because we've become greedy for hp. And cars with big motors still have relatively bad FE, even if you try to drive them efficiently and slowly. The car companies don't have much incentive to sell small, light cars with small motors, because those cars also have smaller profits. And selling a hybrid is a lot more profitable than selling a car like a VX. "even a VX looks sleek and aerodynamic compared to the overly tall small cars you see today" The VX looks sleek and aerodynamic because it actually is. Its coefficient of drag is 0.32. That's pretty low. "small cars tend to be MUCH less sleek these days than larger offerings" I don't see any evidence of this. The new Civic and Prius (for example) are exceptionally sleek. references: https://auto.howstuffworks.com/1980-corvette.htm https://auto.howstuffworks.com/chevrolet-impala23.htm https://www.motortrend.com/roadtests/...ecs_price.html https://www.edmunds.com/new/2008/chev...162/specs.html https://en.wikipedia.org/wiki/Automob...g_coefficients |
dont forget those old boats were ment to be towing a camper going 80 on the interstate. While they didnt have much HP those boats had a buttload of torque.
nowadays its a virtual race to see who can get to walmart fastest, who can show off to their neighbors, and bragging rights about hp and 0-60 times, etc... also something we haven't touched on is rim sizes, nowadays its who can have the biggest rims on your car. Back in the 80's- early 90's cars had narrow small tires. Nowadays a 12-14" rim is unheard of. The public is expecting a ride quality liek sitting on a lazyboy. Only way to do that is increase the tire size and width...Not to mention the interior layout(width, number of armrest, cupholders, etc) hell my chevette doesnt even have cup holders! had an AM only radio with ONE speaker(could get it without the radio) no ac, no power anything...Nowadays if you try to get a car without AC they look at you like your crazy... i blame todays society really, were all expecting a Cadillac ride out of a pinto sized car, it just aint gonna happen! |
I don't think cars in general have gotten heavier than what they used to be. They've gone to use a lot more lighter materials, like aluminum, plastics and composites. The difference between a complete cast iron motor and an aluminum one could be several hundred pounds.
The horsepower aspect of it goes with American culture. Its cool, hot and sexy, while econo boxes and ecofriendly cars traditionally aren't. Sure, I'd love to get back into another Mustang, but having a family, I'll stick with the two Saturn Ions we have now. If people bought vehicles that actually suited their needs and not their wants, you might actually see a different picture of vehicles on the road, and fuel costs accordingly. But as is the case with Americana, its always bigger, better, faster that sells. The automakers have known this all along, which is why fuel economy standards, the CAFE standards, hadn't increased in decades. No one will built cars that people won't buy. When you see gas hit $5/gallon just for regular 87, then you might actually see people change their minds about what they drive. |
"I don't think cars in general have gotten heavier than what they used to be."
It's true that certain lighter materials are used, but I think cars in general are heavier. For example, take into account that in many households, the family vehicle is now a pickup or SUV. These are obviously heavy. Minivans are popular, and heavy. And lots of individual models have gained weight. A Civic now weighs more than an Accord used to weigh. A '77 Accord weighed about as much as my '95 VX. And it got by with 68 hp. The original Civic (1973) weighed 1500 pounds, and had 50 hp. Civics today start at about 2600 pounds. Makers have a large profit incentive to only sell cars loaded with toys. And buyers have been happy to go along with this. |
I'm kinda surprised no-one has touched on the other important reason for low mpg's in modern cars: Ever tightening emissions regs.
People often equate low emissions with high efficiency, but that is simply not true. Lean burn technology like the Civic VX used is much much harder to do, due to tightening of NOX regulations. Also, weight HAS gone up significantly in spite of the improvements in technology. Just compare the 2008 Challenger to the 1970 Challenger. The 1970 had drum brakes, steel body, cast iron V8, etc etc, and yet weighed 700-800 lbs LESS than the 2008. Safety regs and extra features are definitely a part of it, but I also wonder if modern automakers just aren't placing much value on weight reduction. . . |
here is some info from the EPA hydraulic hybrid document:
Losses of energy: Fuel conversion-engine 25.56 in-7.788 out Powertrain 7.788 in-6.359 out Wheel slip 6.359 in-5.507 out at wheel losses 4.965 Aero and Rolling out Resist Energy .0962 This is for a military HMMWV but the figures are fairly close for most vehicles Figures for vehicles (overall averages-passenger car) EPA city cycle Brakes-40% Aero drag-29% Rolling resistance-31% EPA highway cycle Brakes-9% Aero drag-62% Rolling resistance-29% The esitmated potential for improvements Mild hybrid-20-40% Full hybrid (series) with conventional engine-60-80% Future full series (advanced engines,improved aero, LRR tires)-100-120% They have a test vehcile that weighs 3800 pounds that gets 80 MPG. I have spent a considerable time over the last 8 years to develop a hybrid drive system that addresses all of the issues with the exception of aerodynamics and tire rolling resistance. As you can see from these figures the greatest room for improvement is in the engines conversion of fuel energy into output power. The most obvious improvement would be to utilize the wasted heat energy in the engine itself. From the first figures you can see that a 1% (from negative to positive) improvement at the engine translates to a 15% improvement at the wheels. The engine is where the greatest potential improvement would be possible, and this has been the focus of most R&D, which is really sad. I say this because the 60-80% quoted improvement could be accomplished with no change in the engine. The simplest improvement would be to use the exhaust heat to generate energy, especially when the catalist needs to operate at 900 degrees to function properly. Put a small self contained steam turbine immediately behind the cat and use the power generated to run all the accessories, including those driven by belts directly from the engine. My focus is on the powertrain, where the extreme improvements demonstrated by radical hypermiling prove a 100 % improvement over current EPA ratings is not just possible but completely doable. The present record for an Insight is 180MPG, at an average speed in the mid 30s MPH. With a truely infinitely variable transmission (my design incorporates the components in the wheels themselves (replacing the brakes on an equal weight basis- selective 4wheel drive) you have the potential for neck snapping acceleration as well as all wheel regeneration, without sacrificing efficiency). Another major advantage is a significant reduction in per vehicle manufactured components. In summary I am trying to describe a car that cost less to produce than anything currently available in the US market, while providing acceleration that could reach the limit of the tires ability to maintain traction with the road. That right, acceleration equal to the 4 wheel drive rally cars on dry pavement. Accleeration superior to any 2 wheel drive vehicle on the planet. In fact the rate of acceleration could be identical to the shortest braking distance of the same vehicle, with every acceleration event reusing over 85%of the energy consumed in braking from the high speed to a stop. After six years of rejections by 100s of organizations, 6 trips to my congressman, etc,etc,etc,etc, I finally got one person to listen and this fall Va Tech will be building a prototype that will demonstrate the design . The threshold of efficiency is 82% wheel to storage to wheel regeneration. That is about 3 times the efficiency of current electric hybrids. The current state of the art is in the low to mid 70% range. My design is not an adaptation of anything existing, it's purpose from the beginning was to allow the techniques of hypermiling to be applied in such a way that the engine is hypermiling (no idle-no low efficiency running) while the powertrain stores the engine produced energy to be applies gradually or virtually instantly to the vehicle depending on the operators desires. How about 0-6 in twenty revolutions of the wheels, about 120 feet. hte weight of the vehicle is relatively insignificant (not totally of course) because you are utilizing that same weight to accumulate more energy storage , every time you decelerate. In hypermiling you must sacrifice energy to reach your higher pre coast speed, due to the exponential increase in aero drag. This system allows you to select any desired speed, and the engine only needs to run to maintain suffecient reserves of energy to provide on rapid acceleration event. No idling No low efficiency operation 85%+regeneration capability Combine this with minimal weight, reduced manufacturing costs, a much simpler and more reliable powertrain, and of course every possible aero and rolling resistance refinement and you can see the potential. The perfect machine (of course unobtainable) would get 5 TIMES the current mileage. What I see is about half of that when the potential is fully realized. regards gary |
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Of course balanced with this is the need to meet safety requirements. I do know that many carmakers make extensive use of modern CAE tools to predict crash performance of new car designs. One use of the tools are optimization routines to figure out ways to reduce weight but maintain crash performance. |
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gary: "Va Tech will be building a prototype"
That's excellent news. I look forward to hearing more news about that effort. I think you're on the right track. The car should be able to automatically do what a good hypermiling driver does: maximize the amount of time the engine is running at high efficiency, and minimize the amount of time it spends at idle, and at low throttle openings (because that is inherently inefficient). dosco: "the carmakers have a very strong incentive to reduce weight" You're right that they save money when they use less material. But it's also true that lighter materials often cost more then heavier materials. Anyway, more weight means more profit for them. When they make a model bigger, and add lots of extras, that adds both weight and profit. |
Hey R.I.D.E. I like the idea of flywheels too, realised how much more efficient they are than batteries. I wanna build a storage flywheel that fits in a spare tire well, that works as a homopolar motor and generator, and fit two homopolar motor/generators to the rear wheels of FWD cars (Or use the wheel rims heh) brake and it dumps energy to the flywheel, then tap it again for acceleration. Thinking of using a simple mechanical commutator modulation device for power control. Also thinking that low voltage pyroelectric generators could be added to the system and could keep the "charge" topped up on long highway runs... such that you might be able to cut the IC motor for 10 minutes in the hour, cruise off the flywheel, then let it suck up waste heat again for 50 mins. Also there's some low voltage pyroelectric-solar tech that might make enough power to keep the flywheel spinning while you're parked... i.e. park at 9 AM with 6000RPM in the flywheel and at 5pm it's still got 6000RPM to get you going, 'coz it sucked up enough sun to overcome frictional losses. Having auto vehicles though, I might be more inclined to set it up to make enough HHO to run the motor off for a short period of time at highway speed, coz that's easier than killing the motor and figuring out how to run the accessories and transmission pump. (Could make for some interesting P+G variations, like accelerate up to 70 at most efficient BSFC, flywheel brake down to 55, HHO "coast", repeat.)
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The simplest bidirectional path from linear inertia (vehicle motion) to storage (flywheel or accumulator) and back is your ideal goal, as long as you dont loose much energy in the storage and return cycles.
Launch assist means taking the unused wheels, like the rear in a FWD car, and replacing the brakes with hydraulic pumps that slow the car down by pressurizing an accumulator or spinning up a flywheel. Those of us who are older might remember the toy flywheel cars. I like the sapre tire area for storage, in either a flywheel or accumulator. Accumulators are hard to beat because their efficency is in the 95%+ range. Any flywheel will eventually run out of energy, while an accumulator can store it for months with no loss. Run flat tires mean you need no spare. Hypermiling has many similarities to a roller coaster, but if you have enough internal storage you have the ability to dampen the inertial differences in normal operation. Its like eliminating the hills (hypermileing) in the roller coaster Its like having two guages one for speed one for pressure, you trade energy states between speed and pressure, the speedometer goes down (deceleration) while pressure rises, on acceleration it's the reverse, depleting stored pressure while accelerating the vehicle. All during a deceleration and acceleration cycle you are reusing stored energy with no need for engine power 90% of the time. The engines only job is to keep pressure reserves in between a specific minimum and maximum, unless you are climbing a steep grade for a sustained period. This is when the engine would have to work the hardest. If that requires a larger engine then the total operation time of that engine would be proportionatelly less, when full power was not needed. Another way to think of it is to be able to toss a bungee cord out and hook it on a telephone pole to stop, then move the pole in front of you to launch yourself back to almost the same speed. Stopping by climbing a hill, then using the grade to get back to speed is exactly the same. Like the skateboarder in the U shaped track who only has to apply energy at the beginning of his run to do many cycles of the ramps. When your storage system has the same efficiency as a conventional powertrain in the complete cycle of pressurize-store-release, you have passed the threshold where there is no trade off. Now you add an engine or electric motor (or both of course) and you can used electricity or combustible fuel without having to have two vehicles, one ofr local and one for high speed distances. The vehicle could operate on either system independently of the other . I am hoping to get 85% but it would really be unbeatable if it could hit 90%. There are only two stages of energy conversion, which by carnots law are the minimum possible. As long as each stage is above 90 % including the storage you would be at 81% total efficiency. The problem with an electric storage hybrid is the stages are at least 3 or more in and the same out, so the losses multiply. This doesnt mean there is no place for an electric drive, it means that regeneration probably should not be electric. Remember when they got the astounding mileage out of the Insight, they really didn't use the electric portion of the hybrid, for this exact reason. The wheel to wheel efficiency of electric storage has too many steps and the compounding of individual losses makes it substantially less efficient. A 500 hp hydraulic pump is not very heavy, and the present ones are good a low speeds but their efficiency dies off at high speeds. Put the pump in the wheel and it is never really high speed. It can use the same bearings as the wheel itself, and the wheel can function as a portion of the pump. With 4 pistons rotating around an offset journal set in the hub, you have a drive. If the journal is adjustable you have an infinitely variable transmission. A launch assist regenerative axle option would have another advantage few understand. Instead of driving at 55 MPH and accelerating to hypermile, you can add the regenerative "drag" to add pressure at constant speed, and then use the "launch assist" to drive the vehicle while the engine is shut off, without changing speed. Now you are hypermiling the vehicle, with absolutely no driver imput necessary, and you are not paying the higher drag penalty of adding 10 mph to your speed. Short term capacitive storage allows you to run the engine at a higher (less fuel per hp) load, while the pressure launch allows you to use a smaller engine. My grandfather was a fisherman who couldn't read or write. They had a Model A Ford. On Monday they put the car engine into the Chesapeake deadrise and used it to fish all week, then put the motor back in the car for weekends. Later on they could afford two motors and didn't have to switch them around. My concept would also have a similar capability, the person who needs no more than a 50 mile range could use only electric drive, while another person with different circumstances migh use only IC drive. It depends on many circumstances. regards gary |
wow, piled up fast...
yea, you spaced out there with the ram rpms thing...they all spin 1/2 crank rpm (assuming 2 valves) one lobe or two, you have x amount of friction pushing against it. as for leverage and all that, the valves must open X amount, you can have a short lobe with a long lever (lots of force, low distance) or tall lobe with short lever (or none. lots of distance, low force) either way, you have X work done and X friction to do it. now if you were to change to a single cam, you'd have half as many bearings holding the cam in the head. or maybe 2/3 as many. but keep in mind even an un-loaded bearing still has some friction 2 valves vs 1 valve: compare the 6MGE to the 7MGE engines toyota used to make. both 3l L6 DOHC engines. one 2v/cyl, one 4v/cyl. power is up 5hp but the whole intake is redesigned, bigger injectors, etc weigh the valves: 24 smaller valves weigh more than 12 larger valves that weight is countered by the valve springs to prevent valve float at high rpm. lighter springs=less friction at the cam. I can also tell you from experience that turning over the 12v engine is noticeably easier than the 24v by hand...as in I an do so with the harmonic damper on the 12v but can't on the 24 (with spark plugs removed) I also agree with the supply/demand arguement for automakers making SUVs, as long as someone buys them, someone'll keep making them |
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Since everyone has their opinions, I?ll throw mine in, too.
Its always the fundamentals. It all comes down to matching road load to engine load and driveline efficiency. The Road Load Equation is (simplified): Road Load = (aero drag) + (rolling drag) + (grade load) + (parasitic load) Aero drag force is that equation we all fret over (constant) x (air density) x (coefficient of drag) x (frontal area) x (speed squared) Rolling drag force is the sum of tire rolling resistance, all bearing drag, and brake drag times the vehicle weight. Grade drag force is the road grade in % times vehicle weight Parasitic load torque is the load imposed by auxiliary equipment the engine has to drive ? such as alternator, and air conditioning. Sum up all the drag forces, multiply by speed time the appropriate constant and you get Road Load HP. Excess (or deficient) driveline torque yields force to accelerate (or decelerate) the vehicle. The parameters of the Road Load Equation that car designers can control are coefficient of aero drag, frontal area, tire rolling resistance, bearing drag, weight, and (to some extent) parasitic load. The car designer cannot control air density, grade, or the nut behind the wheel. A car may be fuel-efficient if it has low coefficient or drag, small frontal area (the ne plus ultra vehicle for aero drag is a street luge), low weight, low rolling resistance tires, low drag bearing, and brakes that don?t drag. The engine efficiencies of modern vehicles are all about the same with one exception: diesels are 25-50% more thermodynamically efficient than gas engines. There is really little new in engine design. Everything in engine design used today can be found in either the work of Louie Mayer or Sir Harry Ricardo. The problem lies in matching engine speed and torque to road load requirements. If you see a small displacement normally aspirated engine that makes a lo5t of power you can bet the farm that it does so at high RPMs. High RPM often means high pumping losses in the engine. In fact the normally aspirated Otto-cycle engine is a resonant device (like a pipe organ). At the torque peak (also max BSFC) the intake and exhaust gas streams resonate with the valves and pumping losses are minimized, hence efficiency is maximized. But engine frictional HP is frictional (machine friction plus pumping work) force times engine RPM, so frictional HP is generally proportional to RPM except at the torque peak. Supercharged engines tend to damp down the resonant peak by simply overwhelming the gas path with air. That?s why the torque peak is nearly meaningless (in terms of efficiency) to a turbocharged engine. For a turbo engine the most efficient operation is at the lowest RPM where the turbo can make enough boost to blow away the resonant losses. In a nutshell, the slower the engine turns the better the overall driveline efficiency. The other part of driveline efficiency is more variable and is important to fuel economy. Torque converter automatic transmissions are dependent on the inherently wasteful torque converter . A manual transmission locks up the clutch the vast majority of the time and does not waste energy. CVTs are somewhere in the middle but offer god matching of engine and road speeds. Mechanical CVTs are dependent on friction and are somewhat power-limited. The best all around would be electric drive (very efficient, flexible and reliable) but this tends to be very heavy. Every gear mesh extracts a frictional penalty. The optimum setup is with the crankshaft attached straight to the wheels but the torque characteristics of the internal combustion engine will not allow this. This was the setup for traditional reciprocating steam locomotives. The crankshaft was the drive wheel. The steam engine makes max torque at zero RPM. That is the overview of what controls fuel efficiency. Everything else just parsing the fundamentals. |
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I worked on cars for 30 years from 1969 to 1999. When disabilities prevented me from continuing I sold my repair shop to one of my employees.
Before working on cars I studied them intensely, my reading skills are very good, read the Bible and the Rise and Fall of the Third Reich at age 10. Around the year 1970 I read about a fuel mileage contest where an Ople Kadett station wagon achieved an almost unbelievable mileage of 124 mpg, in a contest conducted by a magazine, I think it was popular mechanics. I never forgot that fact, although at the time fuel mileage was the least of my concerns. I was making about $200 a week take home and gas was 32 cents a gallon. My take home paycheck would buy 600 gallons of gas a week, the equilavent of $1800 per week takehome today. I used to play an online flight sim called Red Baron. A group of people who played the sim had a get together at Old Rheinbeck Aerodrome near Kingston New York and during the two days I was there I had a chance to look over an original Rotary Aircraft engine. It was a Gnome version and it was cut away so you could move it and watch things work. I had read about rotaries before but never really focused on how they worked. The fixed crank spinning engine block was fascinating, and after some study I realized that this was not a reciprocating engine, even though the pistons moved up and down in the cylinders in the same way a conventional recip engine did to produce compression and power, with one huge exception. In a conventional engine the combustion pressure pushes the piston away from the cylinder head, in the Rotary the same pressure pushes the cylinder head away from the piston. There is no reciprocation in an original aircraft rotary engine, displacement is accomplished by different axes of rotation in much the same way as a rotary vane pump, used in high speed "peanut" grinders and other tools. Its was funny that the rotary vane pump was something I used in diagnosing vibration problems due to wheel and tire problems in my shop. We used a peanut grinder to spin the wheels on a car up to close to 100 MPH to check for vibrations after retracting the brake pads on the front wheels, and moving the wheel to the front of the car if necessary. This was a tool that produced so little power you could hold the disc in you hand an pull the trigger with out the disc spinning, but you could spin the tire-wheel combination up to enough speed that if you grabbed it it would rip your arm off. I looked up rotary engines on the web and found some interesting information. There is a rotary engined car that was donated to the Smithsonian in 1899 by a man named Stephen Marius Balzar who built it in 1893. There was a motorcycle built in Germany in the twenties that had a rotary engine in the front wheel. It was called the Megola and was competitive in racing in that time period. Of course the original engines were battle tested, and I though it rather funny that the original aircraft rotary was one of the only designs that did not evolve into an automotive application since almost every other innovation originated in aircraft design. In conversations with a friend who is an MIT graduate and works for NASA I realized one principle that had not been applied to the original rotary engine. In the originals the crankshaft was bolted to the airframe, and provided the locating point for the main support bearings that the rotating engine block utilized. My thought was to separate that support function from the crankshaft. Now you could bore an offset hole in that support housing that allowed you to rotate the crankshaft to a position that eliminated all motion of the pistons relative to their respective cylinders. Voila, now you have an engine that can almost instantaneously transform itself into a flywheel, utilizing the mass of the engine block as flywheel storage, you have the ability to combine power generation and high capacity storage in the same component. Understand this, in a 60-0 deceleration in a 2500 pound car with a 250 pound engine, you only need to increase the engine speed from 2000 to 3600 rpm to store the energy. I am not talking about a high speed flywheel with all the inherent danger, quite the contrary a low speed engine-flywheel especially one buried in the front crossmember of a FWD car (corssmember acts as scattershiedl) is completely doable. There are a lot of other problems with the original rotaries that would condemn them to the scrapheap today especially in the light of current emissions requirements. I focused almost 3 years to developing solutions to those issues ,and I believe I have addressed them all. Unfortunately like the priestress Cassandra of Troy in Greek mythology few people believe me, and it's understandable when you read the post above that states there is nothing new in engine development. 100,000 other dreamers with failed ideas are a tough barrier to pierce with your inspiration. After a lot of time and energy trying to solicit interest in the engine configuration. I was building a model that demonstrated the function of the design I was trying to demonstrate. They say a picture is worth a thousand words. A demonstration model is worth a thousand pictures, and all the words in the language spoken in this forum. I used a part of an old 240Z fan clutch, specifically the hub and back part of the outer housing to build a model. I had a machinist make a journal that could be moved from the center axis to an offset axis, and made four pistons and cylinders out of wood and aluminum tubing, and the eyelets on a screen door that hold the spring in place. Each piston and cylinder looks just like a hydraulic ram with an eye on each end, and they rotate around the center journal with the outer rim of the housing of the fan clutch. When you move the journal to the central axes the pistons do not move relative to their cylinders, at any position other than dead center the pistons stroke increases as a result of differential rotational axes, at twice the distance of the distance the journal moves. By pure luck the pistons I had built were reversible, They could be configured as the original rotaries with the connecting rods attached to the crank journal or they could be reversed with the cylinders rotating around the center journal. This configuration also had no connecting rod, instead the piston and "rod" were the same unit. Since the cylinders could rotate at one end and the pistons could also do the same there was no necessity for a connecting rod. With the cylinders rotating around the center journal all displacement variations occur over the center of the assembly and do not create imbalance problems as they would if displacement occured at the perimeter. 4 cylinders create harmonic sinusoidial waves, which means reagrdless of the displacement the flow of fluid through the pump creates a constant pressure which needs no dampening for pressure oscillations that would feel like a clutch chatter. Imbalance or chatter would be hard to resolve otherwise. I used to drive around and play with this model when I was stopped at a light or stuck in traffic, and it dawned on me that it might be a better idea to use this configuration as a hydraulic pump instead of an engine. Another inspiration was understanding that the core component of my design was the same comfiguration as any axle&hub that was used on any wheeled vehicle ever made, one of the oldest inventions of mankind. Enlarge the axle to allow the offset crank journal (adjustable) to be positioned in the hub and you have the ability to power the hub and wheel directly using hydraulic pressure. You also have the ability to convert the linear motion of the vehicle into hydraulic pressure by reversing the stroke position from positive to negative. In essence you can apply a braking force by making the rotating wheel produce hydraulic pressure, which can be stored in an accumulator or a flywheel. Basically this means you have the potential to recover almost all of the inertia stored in the moving mass of a vehicle as hydraulic pressure to be reapplied as accelerative force. Think of it as using the arresting wire on an aircraft carrier to capture the energy of stopping the plane, and reusing that same energy to shoot another plane off the deck. A good analogy is the "smart bomb" where you take a dumb bomb and add components that allow you to guide the bomb to the target. A smart axle allows you to reuse wasted braking energy and reapply it for acceleration. As long as you have accumulated pressure you can launch the vehicle one time to a very high speed, brake and recover that same energy many times depending on the efficiency of your system. At 90% it goes 90,81,72,63,54,46, etc, with no engine power necessary. Thats only part of the advantage, the other part is the fact that when you add any engine (or motor) whether electric or IC, all the powerplant needs to do is maintain a pressure (or flywheel speed) reserve capable of one full acceleration event. In the case where you had a charged accumulator (or flywheel) the system would need to be capable of storing two events. In long downhill situations additional storage would increase efficiency. Now you have disconnected the engine form the power application of the storage and powertrain and the engine can be operated only at its highest efficiency. Hypermiling demonstrates the effectiveness of this operational tactic. The increased efficiency of the vehicular system when hypermiled goes beyond the increased engine efficiency of the engine operational tactic alone. You can not rationalize the doubleing of mileage in a hybrid utilizing hypermiling as an increase in engine efficiency. In fact when hypermiling a hybrid the electric portion of the vehicle is not used other than restarting the engine, and represents carrying excess weight if you understand what I am saying. In the latter part of this year Virginia Tech will (according to our agreement) design and build a protoype, do all CAD drawings and test this design for efficiency. If the design exceeds 82 % ( I think it will hit 90%) it is as efficient as a conventional manual transmission drivetrain, so there is no trade off involved in implementation. In fact the opposite is true, due to the fact that my design is so simple that it will reduce by 15 to 25% (depending on configuration) the number of manufactured components PER VEHICLE. Now you have a "hybrid" that can have astonishing acceleration, regenerative braking, and be virtually maintenance free, as well as cheap to build. Imagine a $10,000 car with 0-60 in 5 seconds, 4 wheel drive (necessary for 4 wheel regeneration) and you can understand the potential. However this is only the tip of the iceberg. The same self contained "launch assist" axle can be installed in any wheeled vehicle. Trains, planes, heavy trucks (as well as light ones of course). The potential for Worldwide improvements in vehicular efficiency are incalculable. The most inefficient current systems (like garbage trucks) will have the greast improvements in mileage (as much as 400%). This is the way to the 100 MPG car, like the Volkswagen of pre war Germany, a peoples car, inexpensive, and totally reliable. When future developements in fuel cells, battery technology, alternate fuels, homogenous charge compression ignition, or anything you can imagine, become practical affordable realities, this system will still be practical when it comes to applying that source of power to the pavement. The problem today with hybrid development is we are divided when we need to be united. We will need to "hang together" or OPEC will hang us separately and drain our national wealth leaving the US as a has been global power. With the current gas prices we are just beginning to react to that threat, and they are betting we will repeat our past mistake of going back to the same old status quo. I can only hope to see the change in my lifetime, but if I never see a cent for my idea, we still owe our children the chance to enjoy the freedom we sometimes take for granted. My 87 year old father put his life on the line for his unborn children. I have been told that the powerful corporations that would be directly impacted by my ideas would stop at nothing to prevent this from happening. Bing it on. regards gary |
"when you try to reduce weight, you have to pay the engineering team to find ways to maintain strength in spite of the fact that the amount of material is reduced"
That's true, assuming that you're trying to produce the same car, with the same dimensions and features (or if you're trying to produce a bigger car, with more features). Then it's hard to cut weight. However, it's easy to cut weight by making a car smaller and/or deleting features (compared with last year's model). But makers don't like that idea because it cuts profits. And customers don't like that idea because for many of us the car is a status symbol, and a means of self-expression, rather than a tool. And also because in many areas we've gotten used to living beyond our means and ignoring the long-term consequences of overconsumption. The excrement hitting the fan at the gas pump is not that different from the excrement hitting the fan in the housing market. We love our big houses, big cars, and big loans. "mild steel is one of the most dirt cheap materials imaginable" Good point (and it's probably more true than ever, since lots of cheap steel is now coming from places like China). You can make a vehicle bigger, more impressive and more profitable mostly by adding lots of cheap steel. I think this is seen in the barges we bought in the Sixties and Seventies. But I think that same phenomenon now pops up in the world of pickups and SUVs. And for those vehicles and others, we've been adding power faster than we've been adding weight. The study cited above by theclencher has an interesting graph showing that acceleration has been improving, even though we've added weight. That means engines have been growing even faster than the rest of the vehicle. |
"My take home paycheck would buy 600 gallons of gas a week, the equilavent of $1800 per week takehome today."
Gas isn't $3 anymore! That was last week (I'm exaggerating the time scale, but not by much). It's now $3.71. So the number in your sentence should be $2,226, not $1,800. "few people believe me" Maybe high gas prices will influence this dynamic. I'm interested in what you're describing, but there are a few things I'd like to understand better. Do you picture the engine block spinning (like on certain old aircraft designs)? Or are you just mentioning that because it was a step toward designing a new kind of hydraulic pump that will live inside each wheel? If the engine block isn't spinning, then where is the flywheel? |
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For me, in fact, it's an embarassment when I drive something that I know makes me look like a shallow wasteful status-seeker. However, I don't allow that to stop me. What it all boils down to is something that I've learned is universally true in every area of life: One size does NOT fit all. Quote:
The scrapyard down the road from my house pays $170/ton for mixed crappy steel stuff and $270/ton for clean steel. I got $16 for a complete refrigerator, which surprised the hell out of me since I thought I was going to have to pay them, considering the cost of the hazardous waste disposal involved. I googled for scrap steel price china and this was the first result: https://query.nytimes.com/gst/fullpag...50C0A9629C8B63 Quote:
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Google "animated engines gnome" for a nice animation by Matt Keveney.
Looking at the moving picture, imagine the offset journal, the central point around which the rods are rotating, as becoming the central point around which the engine is rotating. That is all that needs to change to transform the basic engine into a flywheel. The devil is in the details, which are to eliminate all of what is called "pumping losses" by many. My design creates a recirculating pressurized lubrication system. That ony functions when displacement is used. In fact all other parasitic losses inherent in a fixed displacement reciprocating engine are eliminated. Other advantages Constant fuel delivery per injector pulse No separate cooling system No need for any restriction in the induction system or any throttle control 1 fuel injector 1 intake port 1 exhaust port No valve train whatsoever,intake and exhaust ports are on center journal and are covered and uncovered by rotating cylinders (similar to a wankel) Crank journal position controls all running functions and disables all of them when in flywheel mode Supercharged (or turbo) with intake and exhaust harmonics due to one port supplying 3 cylinders 2 or 4 cycle selective operation, but I prefer 2 cycle compression ignition possiblysome configuration that would be similar to orbital engine Cooling accomplished by recirculated oil throught a radiator with thermostat to bypass radiator during normal pulse and glide operation, cooling system would activate automatically at high speeds or sustained grades. Hot exhaust gasses can preheat intake air charge, due to lack of throttleing or huge variables in engine fuel delivery, homogenous charge compression ignition becomes practical which eliminates any necessity for post combustion eshaust treatment. variable compression that can be fine tuned for specific load situations, multifuel capability with compression tuned for optimal performance lack of valve train means piston crown can be configured for extreemelyclose tolerances with journal face, possible compression ratios significantly higher than current diesels. engine keeps spinning even when no fuel is delivered so no restart is necessary with stroke in flywheel position you could spin engine by hand easily you could even have an emergency dead battery option where you could pump up the hydraulics using human power to provide rotational force to start engine Additional cooling could be accomplsihed by delaying the stroke position movement and letting air flow through the engine in direct contact with the hottest parts, much more efficient that trying to cool the outside. Total time to R&R and rebuild thsi engine would be only a couple of hours with in wheel transmissions each wheel has a independent drive capability completely compatible with traction control and abs about 1 hour labor per wheel to replace or rebuild the in wheel drives parts gone for each vehicle complete cooling system any throttle control or part throttle controls flytwheel(torque converter) driveshafts axles differential brakes (except backup emergency brake) The engine would be buried in the front crossmember in one configuration in lieu of flexible hydraulic transfer lines the fluid would pass through the suspension locating links to eliminate the potential catastrophic fluid loss in the event of a line failure, sensors would detect leaks and disable that section of the drive vehicle could limp home on a single drive wheel (out of 4) since "gear ratios" are infinite the same vehicle could be a high speed freeway cruiser or a rock climber with hydraulicly adjustable ride height and full time selective on the fly 4 wheel drive. My R&d time is in the several thousands of hours, this is all form memory without consulting any notes. regards gary |
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