How do you figure?When torque is multiplied, power is reduced.
ZV
How do you figure?When torque is multiplied, power is reduced.
ZV
I only noticed one neat thing while driving my dad's ford 500 with a CVT. If you are going down a hill steep enough to gain speed while coasting it will automatically pick the right gear ratio to maintain you current speed using engine braking.
Think of it like this. If I want to accelerate as fast as possible because I'm hauling rocks with a Corolla or I'm just trying to get up to highway speed and I don't want to die, where should the engine's RPM be? Some will say max torque but the real answer is max power.
How do you figure?
Imagine you are riding a mountain bike up a hill. You downshift to make it easier to pedal, why?
Pedaling becomes easier because through a ratio of cogs, you have amplified the amount of leverage you have to turn your rear wheel (torque), however, now for each rotation of the pedals, the rear wheel turns a smaller distance, doing less work, therefore each rotation is effectively less powerful.
That's my understanding anyway.
Is there some kind of problem with variable transmissions that would cause so many car companies to avoid them like the plague? Cars like the Toyota Prius and Honda Civic Hybrid use variable transmissions, but every other Toyota and Honda non-hybrid uses a conventional fixed ratio automatic. Why is this?
bignate already mentioned this on the first page. Toyota calls it a Hybrid Synergy Drive. By using a gasoline engine and an electric motor, both power sources can be used at the same time and it can act like a variable transmission.
What's really neat about this planetary gear system is that it's not using belts or chains or anything weak like that. It looks a lot more like a conventional automatic transmission; the kind of transmission that be hooked up to V8 engine without breaking.The Toyota Prius is packed with some pretty high-tech stuff, but at the heart of the Hybrid Synergy Drive (HSD) is a simple little device called the Power Split Device, or PSD. The PSD is a planetary gear set that removes the need for a traditional stepped gearbox and transmission components, and also the familiar rev-lurch-rev-lurch of acceleration in an ordinary gas powered car. It acts as a continuously variable transmission (CVT) but with a fixed gear ratio.
The engine at max power will accelerate faster because it has greater torque multiplication through the transmission.Lets say you had two equivalent engines [two toyota corolla engines ] each connected to a dynamometer via a transmission. One engine is brought up to the RPM where it makes max torque [4000 rpm] and the other engine is brought up to where it makes max power [6000 rpm]. Suppose the transmissions connected to each engine are designed to have the dynamometers rotating at some given speed.
If you suddenly fully-open the throttle for each engine, which dynamometer do you think will be accelerating the quickest?
Test drove a Subaru Outback with CVT today. Drove up some steep hills on the highway and CVT was really slick. Hope to test drive an Audi Q5 soon which has a 8 speed automatic.
How do you figure?
Original thought was:
HP = TQ * RPM/5252
To multiply torque, RPM goes down. Reduce RPM and you reduce power.
However, now that I think about it, the factor by which TQ increases is the same factor by which RPM decreases, so power should remain constant. Oops.
ZV
TWhen you see torque vs horsepower curves they are actual measured values from a dyno, not calculated results, right, otherwise every curve would show the HP and TQ cross at 5252 RPM
Shawn's right about every dyno showing HP=torque at 5252RPM... there's no reason why it wouldn't be the case.The funny thing about that equation is that when RPM<5252 HP is always less than torque, when RPM>5252 HP is always greater than torque assuming torque is constant. Torque isn't constant at all RPMs, nor is horsepower. When you see torque vs horsepower curves they are actual measured values from a dyno, not calculated results, right, otherwise every curve would show the HP and TQ cross at 5252 RPM
Maybe I just found a poor example of a horsepower curve, this certainly does not cross at 5252 rpm
Because the scales are different
Look at the Y axis. The dark line uses the right side and it's near 296 at 5252. The light line uses the left side and it's slightly below the 299 line at 5252.RPM is RPM for either scale
Motor power is low for the left part of the graph because the motor's power factor is highly inductive at low speeds. The frequency of electricity going through the thing is thought of as f*s where f is frequency of input (usually 60Hz) and s is slip. From a dead stop, slip is 1, so frequency is 60. When the thing is running at 0.95x synchronous speed, the frequency of electricity in the armature is only 0.05x60 = 3Hz. The reason the frequency makes a difference is because the impedance of an inductor is directly proportional to the frequency. At 60Hz frequency, the circuit is strongly inductive, so large current does not mean large power. At something like 3Hz, the circuit is mostly straight resistance, the power factor is a lot better, so the real power is higher even though the current is less.Consider an electric motor:
As RPM increases torque remains fairly constant but current decreases, current can be converted to watts by multiplying the current by the input voltage, which results in a curve that follows the current curve to zero at high RPM. KW can be converted to HP by multiplying by 1.34, so the horsepower curve would follow the KW curve to zero as RPM increases. The horsepower curve calculated by measuring the current looks very different than the curve calculated by converting torque to hp.
RPM is RPM for either scale