|
|
Transmission choices present and future.Feb 16 '05 Write an essay on this topic.
Popular Products in Cars
The Bottom Line Various types of automatics are the way of the future, but manuals are worth learning here and now.
It's often reputed that the manual transmission isn't going to go away anytime soon. Even if some technological advance comes along that subsumes the manual in terms of its effective capacity, there's nothing beating that feeling. There's the man and machine connection that can't be outdone by any other means. Of course, that sounds great when you're taking this relaxing continuous drive down an open road or highway... life doesn't always work that way, unfortunately. We drive in parking lots and in stop and go traffic and rush hour on the way home from the office. It's inescapable. We wouldn't even be able to afford our cars if we didn't tough that part out. But these are the kinds of things that kill the "fun" argument of manuals. I myself have always been used to automatics. The only manual transmission vehicle I've ever had was an old Vespa scooter. Manual transmission in a car is something new to me, but I'm in the camp that it's something worth learning. And I really don't believe it's something that should really be considered as impossible for some people or that "some people aren't made to drive stick." If that were true, what did people do prior to the existence of an automatic? You can argue about performance and gas mileage, but arguments like that are doomed to fade as technology advances. Still, it's something that does hold true here and now. Modern automatics have some methods by which they can approximately match the effective fuel efficiency of a manual. Not the least of which is a mechanism that locks the shafts of the torque converter when the two turbines nearly match up in speed. It doesn't really help you that much insofar as getting that better acceleration because it does take a while for these speeds to match up. But once you're going continuously for a little while, it all works out. This is why you might see a handful of cars where the mileage difference between manual and auto is very small or sometimes non-existent. For instance, the Civic EX is rated at 32/37 with a manual and 31/38 with an auto. Who'da thunk it? Still, as great as this all sounds, it's not a very common thing. You're not going to see specs like that on a Chevy compact. However, part of the annoyance of buying a stickshift car is finding one. More often than not, you go to the lot or the showroom, and nearly everything they have is an automatic. BMW dealers or sports cars are a different story, but in those cases, a manual is considered a point of honor more so than an option for you to choose between. Also, youth-oriented vehicles like Scions or Mazda3 or Matrix are often more available in manuals because young drivers will look in that direction. That doesn't help you much if your married with 2.5 kids in a 2500-sq. ft home in the suburbs and you still want a manual. At the same time, it's not always valuable to look for a manual if you've got your 2.5 kids and all. People often say that driving a manual helps keep your mind on driving. But that can be a double-edged sword if you've got screaming kids in the back and objects being thrown around. In general, I think the younger you are, the better the time to buy a manual. You're typically in the market for a car that costs less. You've got an entire lifetime to perfect the art of shifting, and you don't have to worry about your significant other borrowing it without knowing how to handle the darn thing. Of course, if you're not entirely free to think in that way, but you still want to learn to drive a stick, then more power to you. Yes, the autos are easier to find and easier to drive, but I still think a manual is worth considering for at least one of the cars you might own in the course of your life if only to get you a better feel for driving. Even otherwise, I might advise a few things even for automatic drivers -- whenever I come to a stop that I know I'll be standing for a while, I usually shift into neutral before hitting the brakes; It's easier on the engine(which gets freed up for a little while) and on my brakes(which don't have to resist engine power). It should be noted, though, that while automatics dominate the lots around the US, the opposite is true in other countries. Try finding an automatic transmission in India. HA! Even the "autos" aren't... autos(we use the shorthand "auto" for "auto-rickshaws"). If you ever have a penchant for international travel, or a job that takes you around the world, learning to drive a manual is extremely valuable. Personally, I would choose to drive a manual for that one particular reason more so than anything else. If you learn to drive a manual, you can basically drive anything. I also think that for the non-gearheads of the world, driving a manual can give you a better understanding of what goes on under the hood and how it affects the way your car behaves. I equate learning a manual transmission to learning to program in Assembler. How does my engine rpm affect my mileage or my engine load? How does it help me in certain specific cases to use engine braking as opposed to the brakes themselves? Will I need to change my oil more often if I live in Seattle as opposed to Chicago? You usually don't think about these things with an auto because you don't get to control these variables yourself. A lot of people criticize CVTs for some odd reason, but who you really should be criticizing are the auto manufacturers who don't do the job right. Technically speaking, the theoretical limits of a CVT are superior to those of any geared transmission, manual or otherwise. There are, however, issues in reaching those limits. The most common type of CVT is the dual twin cone variator pulley. This involves two shallow cones facing each other that can vary their distance apart. This forms one pulley. One pulley needs to do the opposite motion of the other pulley in order to keep the belt/chain in tension. This is the type of CVT you'll find in the Audi A4, the Nissan Murano, etc. While it sounds neat to be able to achieve these really high overdrive and underdrive ratios and everything in between, this type of CVT is too flimsy for very high torque loads. It is only recently with new belt and chain designs and new alloys that we are finally able to even link this type of transmission to a V6. It is also very liable to experience losses due to clamping pressure on the belt in order to maintain friction. Audi dealt with this partially by designing a chain that has connecting bolts deliberately sticking out. These bolts also make contact with the pulleys and experience enough pressure that the lubricant fluid undertakes elastohyrodynamic conditions -- that is, under that pressure, the fluid starts to become semi-solid, and resists shearing. It also depends on some very smart computer control as well to make sure that the pressure is actually achieved. As a result, Audi claims that their CVT outperforms their manuals both in acceleration and mileage. Nissan tried to deal with the flimsiness of the design by using a reinforced belt and reworking the clamping pressure algorithms so that the belt is actually in compression rather than in tension. As a result, they're able to link it up to a more powerful V6 than Audi can. Nissan also has a different kind of CVT that you don't really see in the US, and is on their Skyline series. Mazda is also experimenting with a CVT of this type -- it's a half-toroidal roller variety. Try and imagine mold for a donut-shape, and then taking that mold and cutting away the outer part (cutting in a circle that lines up with where the donut would be widest). Now you lay the mold on the table and cut in half along the horizontal plane -- so now you have these two halves which can sort of cradle a donut. One of the halves is connected to the engine and the other is connected to the output shaft of the transmission. A roller disc or hemisphere connects the two halves. The angle of the roller changes the ratio. Might make a little more sense if you look on JATCO's site -- http://www.jatco.co.jp/E_JATCO/PLAZA/TEC_E.HTM The CVT used in the Toyota Prius is yet different, and is a devilishly clever design, which is very hybrid-oriented. This is the type of transmission I'd expect to see on most any parallel hybrid vehicle in years to come. This one is based on a sun gear, a set of planetary gears on a moving planet carrier and a ring gear with teeth on the inside. The sun gear has 30 teeth, each planetary gear has 23 teeth, and the ring gear has 78. The engine's output shaft is connected to the planet carrier, the sun gear is connected to the electric motor, and the ring gear is connected to the generator as well as to the output shaft & differential. By controlling the rotation rates of certain gears, you get a CVT as well as a power splitting and sharing mechanism. Unlike a normal CVT, the torque-multiplying effect is lost and instead, you acquire extra torque from the electric motor. Either way, this isn't a normal CVT, but more like a differential that is explicitly designed for hybrid powertrains. In this type of setup, though, it's not a question of whether a manual would get you better gas mileage or performance -- an ordinary gear transmission simply wouldn't provide the same function. Some basic calculations on the computer control algorithms make fuel saving very easy. e.g. Say you want to save gas by having the ICE run at 1500 rpm at 55 mph. Based on the final drive ratio and the size of the tires, the generator would be turning at 3250 rpm at 55 mph. Which means that for the ICE to turn at 1500 rpm, the electric motor would have to turn at 3051 rpm backwards. For a more complete explanation -- http://home.earthlink.net/~graham1/MyToyotaPrius/Understanding/PowerSplitDevice.htm There are promises of yet better designs such as the Anderson CVT and the Torotrak IVT. BTW, the only real difference between an IVT and a CVT is that an IVT is supposed to also be capable of 1:0 and 0:1 ratios as well as reverse ratios. Leonardo's ca. 1490 rolling disk CVT design would qualify as an IVT. One thing I happen to like about the Anderson CVT design is that it's very well-suited to a sort of "manual CVT" setup. What remains to be seen about the Anderson design, though, is how easily or well you can scale up that floating sprocket bar idea to very heavy torque loads. Torotrak's IVT is clearly capable, as it is based on a variator design that is hooked up to massive gas turbines, but it's a difficult sell and there are yet to be any major improvements to the algorithms it uses so that it can be applicable in many conditions. Yes, it can enable you to make 80 mph at idle rpm, but they haven't worked out things like helping you climb up a hill. Anderson CVT - http://www.andersoncvt.com Torotrak IVT - http://www.torotrak.com Ultimately, I personally happen to think that even if there are technical advances that subsume manual and automatic transmissions, there still may not be a total absence of manuals. With CVTs and IVTs, there is still a place for a clutch, but in this case, the clutch would be more of a toggle that connects or disconnects the transmission, and wouldn't really be involved in shifting. Of course, in the extreme long run where electric vehicles might be perfected, the ultimate outcome would actually be not having a transmission at all -- there'd be a separate motor at each wheel. In that light, it may be worth phasing out the stickshift, but I still think that I won't live to see the day that even a large fraction of cars on the road are electric, so I'm not worried. Until then, happy shifting.  |
| Read all comments (5)|Write your own comment |
