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Thread: CVT's and Computer Controlled Valvetrain Idea

  1. #1
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    CVT's and Computer Controlled Valvetrain Idea

    A week ago I was staying over at one of my friend's house who really likes cars and enjoys talking about them with me. A few of the things that came up in our conversations were CVT's and Valvetrain Systems. First off we were wondering why the CVT hasn't completely replaced the Automatic Transmission yet. I had never heard anything bad about the CVT, only good things. The automatic to me seems so out of date and old when you could have a CVT. Manuals should still be kept around but who needs the automatic now?
    Another thing is would it be possible to have a computer controlled valvetrain system in which a computer reads the RPMs of the engine and then depending on the RPMs it would open and close the valves to maximize power at that RPM. I mean they have things like drive-by-wire and steering angles that adjust to your speed and all kinds of other computer controlled things in cars so why not this? Would the computer not be able to process fast enough? I don't know enough about computers but i would've thought they could. I can see a major advantage from a system like this if it was possible. What do you think about this idea? And i was also wondering if anyone else has ever thought about this.

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    One problem with CVTs is that they can't handle large amounts of torque. Some people don't like them because they seem unnatural. Also, I'm not sure that they are any more fuel efficient than a regular automatic transmission.

    As far as the computer controlled valvetrain: BMW for one is working on this. The problem, if I remember correctly, was with the valves snapping shut rather than easing shut as they do with a camshaft. Also, having powerful enough magnets and electromagnets to operate the valves at 6000+ or whatever RPM is going to be tough.

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    CVT's have been fitted to F1 cars, they can handle the power OK Problem is that they slip, and need a hydraulic pump running, so they cant match the efficiency of a manual. Not sure how they compare to a regular automatic though. Then being a relatively new technology they're expensive.


    There are experimental engines around using hydraulic rams or electric solenoids instead of a camshaft, that allows a computer to adjust the timings to suit the conditions exactly. Problem is the actuators cant run at high speeds (yet ) and draw a fair amount of power.

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    Well Nissan has experimented a lot on CVTs. In fact they offer their CVT on numerous mid-displacement models. The 230 flywheel hp Murano with the CVT has only 140 WHP (i think) this is too low.
    The prob with CVT is that it has a lot of friction. The conventional manual has about 10% power losses, whereas the CVT about double the figure.

    Concerning Active valvetrains, I don't think that they will be magnetic, as they are too expensive and space consuming. The industry has invested a lot on Hydraulic Valve actuators. They do exactly the same job with magnetic ones, but they are far cheaper. Lotus evolved such a system and sold it to Eaton. They are believed to have sold it to a major US manufacturer. But nothing is official yet, so don't hold your breath

    The way to go for petrol engines is the following
    -variable compression ratios (established engineering firms such as prodrive have evolved production ready solutions)
    -direct injection (already used by many manufacturers)
    -Active valvetrains
    -Sparkless Ignition (the mixture combusts due to the pressure from the piston-very economic and reduces NVH substantially)

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    F1 engines use hydolic-acctuators now, if im not mistaken renault (when it was still Benneton) was one of the main developers. But there are several production versions of variable valve timing systems (honda, toyota, subaru, etc...)

    dont know much about CVTs. regarding there use on an F1 engine as was said above, the engines used now have very little torque, especially from low rpm. ive read that the clutches get just a little over 400 Nm (WRCs put through about 650Nm).

  6. #6
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    the CVT is not an "new"invention as stated above.the first CVT was placed in 1960 DAF car, mainly sold in the netherlands !!! As far as i know the CVT has only been placed in a F2 car, long ago.in the old days CVT used to have (rubber) belts.Now they have steel/aluminium belts for durability.

    The main problem with CVT's used to be that they cold not handle higher powered engines.A few years ago this problem was solved.The Nissan Murano was one of the first cars with 200+ hp to have a CVT installed.

    Its true that it does provide a bit of an weird ride, but it is easy to get used to it.after a while you wont notice that you drive a car with CVT anymore.You do get a better performance though you will beat every car at the traffic light

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    Quote Originally Posted by johnnyperl
    F1 engines use hydolic-acctuators now
    F1 cars use pneumatic technology. They use the air as the car runs at high speeds. This technology can't be used in road cars. Imagine being stuck in traffic with minimal average speed.

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    Quote Originally Posted by lightweight
    F1 cars use pneumatic technology. They use the air as the car runs at high speeds. This technology can't be used in road cars. Imagine being stuck in traffic with minimal average speed.
    WHAT ?????

    The F1 cars speed has nothing to do with the actuators

    Think there is some confusion !!!!
    "A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'

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    Quote Originally Posted by drakkie
    As far as i know the CVT has only been placed in a F2 car, long ago.
    I think that Williams tested one back in 1994. Without any development they broke the track record by 2 seconds in one evening. With proper development I suppose that the gains would increase.

    The thing about CVT's in a race car is that the engine works constantly in the RPM that the engine produces max power. For example if this year's Williams engine produces 900 bhp/19000rpm, then a CVT F1 would run for 1,5 hours on 19000 rpm (except maybe the launch in order to minimise wheelspin). The thing that would vary will be the gear ratio.
    The engine and the cooling devices would suffer as a result of the above

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    Quote Originally Posted by lightweight
    F1 cars use pneumatic technology. They use the air as the car runs at high speeds. This technology can't be used in road cars. Imagine being stuck in traffic with minimal average speed.
    oh, your right. that was a brain-fart.
    but matra is quite right. the speed of the engine/car has nothing to do with their function. for example, its similar to the alternator. you can have your lights, AC, wipers and radio on at idle with no problems. if the compressor and storage tanks are designed right there would be no problems at any engine speed.

    probably the biggest limiting factor is the added complexity which raises the price and decreases the reliability of the engine (see F1 )

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