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30 Oct 2002, 11:55 (Ref:417306) | #26 | |||
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Yes, at the rear axle. And yes too, standing still starts. The theory works in static (or instant) case, but not in a dynamic model.
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8 Nov 2002, 07:55 (Ref:424416) | #27 | ||
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So alfasud.
What's wrong with developing a motor with 1000Nm of torque at 5rpm and using the gearing to get the revs need at the rear wheels for speed ? |
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9 Nov 2002, 19:27 (Ref:425245) | #28 | |||
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Now if you want an example of engines operating in the range of 70 to 110 rpm look at engines in large ships. They are very efficient in terms of fuel economy but a 100,000 Tonne ship does not care about engine weight. Ships engines can be huge. Your car does not want a very heavy engine. So car designers run them at high speed to give you the power and gearing (CVT or any other) to achieve the desired performance. Add lightness as Colin Chapman used to say, that adds performance and economy under acceleration in a car. Does that help? |
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11 Nov 2002, 05:59 (Ref:426149) | #29 | |||
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11 Nov 2002, 06:05 (Ref:426152) | #30 | ||
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Yes, if the engine only does 5 rpms. It can however be designe with a 10 rpms limit; it probably won't give you 1000Nm at 10 rpm, but a 5-700 will. Anyway, if the rear axle does 5000 rpm them you don't want to accelerate anyfurther unless you want to take off.
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11 Nov 2002, 21:56 (Ref:426645) | #31 | ||
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thats a good point in disguise. the problem with the 5 rpm enginewould be the gear ratios required for high speeds would lead to some enormous gears that would have a lot of rotational inertia and would work against acceleration
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13 Nov 2002, 01:57 (Ref:427464) | #32 | ||
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1000Nm of torgue at 5rpm?
There's this simple formula of how to calculate horsepower achieved... Torque x Engine speed) / 5,252 = Horsepower So...1000 x 5 / 5,252 = 0.952 hp For a lawnmower it'll work i guess |
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13 Nov 2002, 15:23 (Ref:427833) | #33 | ||
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The Williams F1 car with CVT was banned.
Prior to its ban it was tested (driver was a very young David C.) Please note it ran at constant revs required for maximum power not maximum torque. Do we need gearchanges in F1, why ban CVT now we have traction control? |
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14 Nov 2002, 06:32 (Ref:428288) | #34 | ||
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.
Last edited by Red; 14 Nov 2002 at 06:33. |
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15 Nov 2002, 00:58 (Ref:428901) | #35 | ||
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No one actually knows how the CVT engine used in F1 and later banned works, the technology was not like what was used by roadcars nowadays.
I know everyone in here says that power plays the important role in a cvt engine but i still say otherwise...i might be wrong but my logic is that in order to maintain the rpm constantly you'll need torgue and with each gear changes without torgue to maintain the rpm & accelarate. certainly there will be a loss of power as power alone can't generate an increase of speed when gear are changed upwards. |
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15 Nov 2002, 03:42 (Ref:428941) | #36 | |||
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So we need to use the right part of the torque curve combined with the best gear ratio to get that max torque at the rear axle and therefore max acceleration. That optimum combination of torque and gear ratio would appear to occur when the engine is operating at it's power peak. As mentioned, there are a few exceptions and special cases..... like a standing start when the rear axle begins with zero rpm.... but these are small part of most circuit based motorsport events. |
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16 Nov 2002, 00:31 (Ref:429651) | #37 | ||
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This is an entertaining thread. I can't leave it without giving kudos to Guisbro Rod H for his clear and thoughtful posts. I especially like the part where the piston apologizes for its poor volumetric efficiency at higher rpms.
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16 Nov 2002, 01:21 (Ref:429671) | #38 | |||
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Torgue makes the wheel spins and usually for average roadcars, when the rpm exceeds 5,000 power will take over. We are still talking about cvt are we? my arguement was that cvt cars even from a standstill position, once the gas pedal is being applied and speed was gradually increasing...the rpm would instantly stay at the max and from there, the gear ratios changes would be determined by the road conditions. By logic....when the rpm stays at a certain level even through any given road conditions and gear changes, then the car would be powered more by torgue rather than power. |
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16 Nov 2002, 13:33 (Ref:429919) | #39 | ||
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Arneal - Thank you for your comment.
Lets remember the original request by Engstudent. We amateurs are attempting to help him to resolve this matter. May I suggest Engstudent contacts some experts in CVT. Could he try contacting Torotrak who develop a most interesting form of CVT, or with their system, infinitely variable transmission (IVT). See:- www.torotrak.com Lets not all flood this small company with e-mails. Could I request Engstudent to report their reply to his query? I have not investigated Torotrak's design to determine if it can handle 800bhp+. I am worried about bringing in a different form of CVT design to this discussion because it might dilute the original purpose of this thread and course more confusion. Jukebox said: "No one actually knows how the CVT engine used in F1 and later banned works, the technology was not like what was used by roadcars nowadays." That statement by Jukebox was true but now Williams have released the information. It was a development of the old DAF design of two pairs of conical cones and a fixed length drive belt. Do I need to explain how it works? The difference was that DAF used rubber belts for each drive shaft after the differential. Williams used a single belt before the differential. The belt was a metal segmented belt similar in design to certain jewellery but large enough and capable of handling full F1 engine power. The choice of a single belt allowed the engine and its crankshaft to be mounted as low as possible. The belt lifted the drive up to the centre line of the rear wheels. So, low engine and low centre of gravity for chassis design for good cornering. Drive at centre of wheels to avoid angled drive shafts and avoid extra strain on universal joint couplings on drive shafts. How did it work? The cones adjusted to lowest ratio achievable by travel of cones ready for the start. Clutch gets car rolling. Revs controlled to produce maximum power required that the tyres can take during start-up. Engine revs rise as Williams pulls away. Video has been shown on Discovery where this engine rev increase can be clearly heard The engine reaches maximum revs, then the computer software takes over adjusting the gearing to achieve maximum acceleration. Why was it banned? Maximum revs (AT MAXIMUM POWER-NOT MAX TORQUE REVS) need to be controlled by the computer to prevent over-revving of engine. The accelerator becomes a control for asking for more power or no power (braking). Computer control of throttle and gears was illegal under F1 rules. Worse, computer control of gearbox required a road speed input into the computer; that meant it would be impossible to prevent Traction Control that was illegal in F1. Yes the powers that be twittered on to the press about the absence of gear change sounds, that was a smoke screen. It was the impossibility to prevent traction control. Sorry if that is a bit long, does it help? Last edited by Guisbro Rod H; 16 Nov 2002 at 13:37. |
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19 Nov 2002, 09:47 (Ref:432097) | #40 | ||
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Just to put my 2 cents in, the higher the engine's rpm the more momentum the engine has requiring less torque to xlr8. And a smaller flywheel etc can be used etc.
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