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Doctorate in Mechanical Engineering, entreprenuer
Interests: diesel and gasoline engines, cars, aircraft, railroads, electric drives
Recent Activity
Roger Pham I am not sure what you are trying to say. GM designed the power train assuming that most of the driving would be electric only but that it would be fairly seamless when it was ICE was operating. Anyway, on engine design issues, engine RPM does not matter. What matters is mean piston speed. Interestingly, most engines run about the same mean piston speed whether they are large ship diesel running 88 RPM or small model airplane engines. Concerning turbochargers, GM certainly has experience with turbocharged engines as they have been building turbocharged engines for more than 75 years (Allison V-1710) and turbocharged cars for more than 50 years. (I had one of the first, a 1963 Corvair Spyder.) Their current 2 liter turbocharged direct injection engine is one of the more power dense engines available for a street vehicle with 136 hp/liter. However there is detonation limit to how much boost you run with a spark ignition engine. A turbocharger is basically a positive feedback device (more boost generates more exhaust which generates more boost, etc) so you can not run a turbocharger without someway to limit the boost otherwise something will blow up. Yes, GM could run a smaller turbocharged engine and they already have current turbocharged engines that would work but they probably decided the cost was not worth the gain as the engine does not run most of the time.
I should have put in a link for the Top Gear Prius vs BMW It is in the 2nd half of the 6 minute clip and the BMW was actually a 400 hp M3 with a 4 liter V8. They got 17 mpg with the 1.5 liter Prius and 19 mpg with the 4 liter BMW. One of the reasons that the Prius normally does so well on fuel economy is that it so under performing that there is little or no incentive to do anything but drive it slowly. The Volt has enough performance and drives well enough in normal driving that it is not an unpleasant car to drive.
Arnold. The Ackermann steering mechanism is a very useful approximation but it is an approximation and is only correct straight ahead and at one steer angle. It gets even more complicated when you consider individual slip angles for the different tires at different cornering loads. If you had individual servo driven wheel steering, you could do a much better job of having a correct solution for different steer angles and for different driving conditions. We build a agricultural harvester and I did the steering design. It has Ackermann steering but it is steer by wire and has 2 hydraulic cylinders but only one sensor. If we added a second sensor, removed the connecting tie rod, and added some more software, we could potentially have a better steering solution. However in our case, in probably will not make a lot of difference as the steering or Ackermann is optimized for the max steering angle. The machine is usually either going straight or making a minimum radius turn at the end of the field. At some point, I would still like to experiment with individual wheel steer. Individual wheel steer would probably make the most difference for high performance or racing vehicles.
I think that the ultimate solution is to have individual motors that can be driven at different torque levels. It would also be best to have individual steering drives so that the wheels can steer independently. The commonly used Ackermann steering mechanism ( ) is only correct straight ahead and at one radius.
I do not think that an Sonic based EV will compete with the Tesla Model S but it may help to push along EV market if they can keep the price reasonable. I also wish both GM and Tesla well in their EV endeavors and I would agree with Davemart that GM might do better by basing their new EV on a larger platform. However, I do wonder about the long term viability of Tesla. I know that this is heresy among some of the reader of Green Car Congress but currently Tesla's market cap (shares outstanding * share price) is about half that of GM which is not realistic and they are not currently making money so they are funding their continued development and production by selling stock. This is not unusual with startup companies but it can only gone on so long.
Henrik, I think that I can explain why the S60D and S85D out accelerate the S60 and S85. If you have sufficient power to induce wheel spin, you can launch faster with AWD. After the initial launch power when you no longer have enough power to spin the wheels, power to weight is more important.
Slightly off subject but I was surprised not to see an article on this Green Car Congress. Apparently GM has announced that they will have a new electric vehicle. This is from an article in today's NY Times "According to a report by Automotive News, the car — which is expected to appear in 2017 — would be based upon the Chevrolet Sonic and have a range of about 200 miles." Obviously not a competitor for Tesla but it will probably be more affordable for more people. If you lived where it snows a lot and there are mountains, you might want AWD. I live in Utah and would have a hard time without AWD or 4WD. I have had to chain up all 4 and use low range but admittedly that was for driving on unpaved roads in inclement weather. Anyway, AWD drive would make the Tesla much more attractive here.
What are they using for fuel? The article refers to 320 hp in our petrol (gasoline) configuration but does not state what fuel is used for the 450 hp version. About the highest specific power of any commercially available vehicle is the GM 2 liter turbo with 272 hp. You can get more power with more boost but you will also have to run a different fuel to avoid detonation.
Roger Pham Thanks for the link. I now have a much better understanding of the process. They are using hydraulics to drive a multi-stage piston compressor with a layer of ionic fluid to insulate the piston from the H2.
It is good that they now have direct injection although they seem to be lagging GM and Ford in providing SIDI. What I do not understand is using a CVT. It may be continuously variable and while it will let the engine run at a more efficient point than simple 4-speed transmission, it is also continuously slipping and therefore continuously wearing and continuously wasting power. So while the engine is more efficient, the transmission is not. It would be much better to run a 6-, 7- or 8- speed dual clutch transmission which are both more responsive and more efficient. Also, if you do not think that a CVT transmission in continuously slipping, you need to brush up on your physics and engineering understanding of traction type devices.
I would like to find some more information on ionic fluid compressors but a quick search on the web turned up not much more than was in the above article. I am assuming that the ionic fluid is contained in a cylinder and moved by an electric field? Also, what else can be compressed other than hydrogen? One source suggested natural gas. Probably not air? I would like to see even a simple schematic of this device.
Davemart Do not confuse HarveyD with science or engineering.
Hey John! Did you know that there is a wind turbine accident about every other day with a blade failure, outright tower failure or a major fire about every week now. Some of the blade failures have resulted in blade parts being throw more than a mile. I would far rather live near a nuclear power plant than a wind farm.
Lad, If you were mayor, it would be smart to have your emergency responders well trained but you would have not authority to conduct inspections as that is the FRA (Federal Railroad Administration) jurisdiction. The Bakken crude is so called light, sweet crude which is the more desired crude and while it is more flammable than heavier crudes, it is not as flammable or dangerous as other materials being transported. Every few days, we have a unit train (~100 cars) of sulfuric acid go thru town. Also, gasoline, propane, chlorine, ethanol, and ammonium nitrate are all transported by truck and train. The really dangerous material in my opinion is LNG. Sooner or later we will have a major accident with a large LNG tanker but hopefully not in the US. I did the math on this once and the largest ocean going tankers have about a mega-ton TNT equivalent energy potential. Hiroshima was less than 20 kilo tons so these tankers have about 50 times more energy potential.
I should add that fuel cell research has been going on since 1838 and we still do not have practical fuel cell vehicles.
I expect that Lithium-Sulfide will be the next breakthru in battery technology. There are a number of people working on the problems and they seem to be making good progress. It is also good to see a major automotive company seriously working with Li-Sulfide. Lithium-Air might render the IC engine to dustbin of history but that is an much harder problem. I agree with SJC and Treehugger on most people not understanding how much time and effort it takes to get a new technology to market. I remember attending a seminar 45 years ago when I was a ME graduate student at MIT. The speaker had a new magnetorheological fluid and demonstrated some of the properties but stated that he had no idea what it could be used for. At the time it was just a laboratory curiosity. It took 30 years or so but now some of the Cadillacs and Corvettes have tunable magnetorheological shock absorbers along with a host of other applications. LED's have been around since 1962 but only in the past few years have they made major inroads in lighting.
Roger Pham I work as an engineer and am also a principal of a small company that builds a relatively high tech agricultural harvester. We use a hydrostatic transmission which is what you are describing for the wheel drives. Electric would be more efficient but a relatively small amount of the total power is used for traction. We also use some hydraulic motors and cylinders for other functions such as conveyor drives and lifts but where we are different is that all of the high speed positioning is done with 375 V electric servo motors. The use of the electric drives gives us a substantial efficiency and maintenance advantage over our competitors. As we go forward, we will be electrifying more of the functions and may add ultracaps to recover some of the available power from deceleration.
Engineer-Poet Your are right in that power is pressure * flow rate and with a variable displacement motor, it is possible to reduce power without throttling losses by changing the flow rate. You do need a variable speed transmission as the pressure gives you torque and the displacement gives you rotational speed. No matter what you do, you will have a less efficient system with hydraulics than you would with electric. However, the hydraulics may have a lower initial cost but would probably require more maintenance.
Would this work? Yes, but. I tried make some reasonable (maybe even generous) estimates and then do some calculations. If you do like my estimates put your own in but no fair ignoring physics. I assume that is a hydraulic accumulator type hybrid but it does not really matter. Anyway, energy is change in Press * Volume. I assumed that change in pressure is about 2000 PSI or 14,000,000 Pa (Newtons/m**2) and the tank volume is 50 liter or 0.050 m**3. Multiplying the two, yields 700,000 Nm or 700,000 Joules. Remembering that a watt sec is a Joule, so a watt hour is 3600 J and a kilowatt hour is 3,600,000 Joules. Anyway, with my assumptions (which may even be generous), you end up with about 0.2 kilowatt hour equivalent. OK, so this would work if you were doing most stop and go but you are not going to get far on just the stored energy. One other fly in the ointment and that is efficiency. With electric power, you can chop the current or use pulse width modulation to control the power. Full on for a few micro seconds and then full off for a few micro seconds. You can not do this with hydraulics. You have to throttle the flow. Even if the system was 90% efficient at full power (which I doubt), it would only be 45% efficient at half power. And we have not even worried about the heat that is lost if we do not immediately use the power. Anyway, this might work OK for mail delivery or trash collection where you start and stop every 50 meters but, even then, my money would be on electric power with ultra caps. This is also how John Deere and Caterpillar bet with their hybrid excavators. Bottom line -- I do not think that this is break-thru technology.
The US Tier 4 Final and the Euro 6 compliant engines are quite clean. In some places, the exhaust make actually be cleaner than the intake air. The real problem is the older engines especially the engines that predate common rail electronic injection. Also, until recently, the EU standards were more lax than the US standards.
HarveyD According to the CIA, the estimated 2014 birthrate in Canada is 1.59/woman. This is well below replacement which needs to be about 2.2 - 2.3 to account for those that die before reproducing. The US is about 2.01 which is still below replacement. Even Mexico is down to 2.29. Most of the countries with really high birthrates are in Africa and the Middle East. Even India is down to 2.51. Anyway, I will stick with my PC suggestion for more education for women. War is so messy. I could suggest getting rid of religion but that is probably not PC. On your other comment, the US is not likely to have high speed rail any time soon except on the coasts as the population density and the distances traveled will not support it.
HarveyD I more Politically Correct (PC) approach would be to support women's education. With education, the population growth rate would fall, the demand for resources would fall in the long term and we might even have fewer wars.
Not sure what this has to do with sustainable mobility but it is interesting. I suppose if I had mounted on my truck, I could eliminate those old smoking vehicles that cross my path. I actually worked briefly on a predecessor to this vehicle almost 45 years ago. It was a tracked vehicle designed to destroy aircraft with a lot power for the laser but the technology was not well enough developed for it to be practical.
There is an interesting commentary in the current New York Times concerning a test drive of a VW Diesel Golf. "But no crossover, and no hybrid for that matter, can do what I managed in the new diesel-power Golf TDI: 60.6 miles per gallon over 75 highway miles along the Jersey Shore. That’s my personal highway m.p.g. record for any American-market car I’ve tested, including the Toyota Prius." "In stark contrast to a Prius, a car in which I feel my life force oozing away with every mile, the VW isn’t a sluggish chore to drive."