Tesla problems

Varying gear ratios and diff ratios will modify the torque at the wheels.

... Phil

Automobile engines normally deliver max torque somewhere in the middle of their rpm range. The actual figure reflects the engines's capacity but is heavily modified by the use of turbo or supercharging.

Basically, torque is the result of how many and how energetic the fuel/air explosions are per revolution of the crankshaft.

.... Phil

On Sun, 13 Dec 2015 17:36:46 -0800 (PST), Phil Allison Gave us:

The stroke length is the main factor. This is why diesel truck engines have such long strokes in the designs.

My 1972 Corolla did 0-60 in a bit over 22 seconds. 0-30 in 12 seconds is pretty sucky.

So, the Volt would achieve 60mph in 24 seconds. Less than two seconds longer than yours, yes?

.... Phil

My clocked 0-60 time in my Volt is just under 8 seconds, and 0-30 in 2.4 seconds

What really counts for acceleration is thrust as applied by the tires to the road surface. Wheel torque produces various amounts of thrust depending on the diameter.

An ICE has a complex torque and HP per RPM curve, with peaks of each at different points, and either may drop rather substantially beyond a fairly narrow range of RPM, so multi-speed transmissions are required for best performance. But the time it takes to shift gears and re-engage the clutch or torque converter must also be considered.

An electric motor can provide maximum rated torque from zero RPM, and it remains fairly flat up to rated RPM, and beyond that, overclocking and field weakening can provide higher RPM at lower torque, but fairly constant power. Also, electric motors are typically rated at continuous power, and can be operated at several times that for smaller duty cycles. Induction motors and BLDCs used in modern EVs typically may be capable of about 2x to 4x, while older technology brushed DC series wound motors have maximum torque and RPM (and power) limited only by winding resistance, temperature, brush and commutator capacity, and mechanical limits (bearings and centrifugal force).

Here is an EV calculator you can play with to determine power needed for propelling a vehicle of a certain mass and frontal area and aerodynamic drag, on a given slope or for a given non-gravitational acceleration. A typical small 3000 pound vehicle moving 60 MPH on a 3% upgrade requires only about 30 HP, and 12.5 HP at 30 MPH.

Paul

One of the things that boys buy a Tesla for is the crazy acceleration. And I bet that's hard on the drive train. And the rear tires.

A pushing force of 1600lbs, neglecting air resistance.

... Phil

On Sun, 13 Dec 2015 20:05:49 -0800 (PST), Phil Allison Gave us:

A longer stroke means that the torque arm length on the crankshaft is longer. It is a direct relationship.

No, it was a typo in my original text. My piece of crap Corolla did 0-60 in

.... Phil

Both of you guys are talking out your rears. Torque depends on many, many factors and you are both over simplifying it. Get the pun? Talking out your "rears". lol

On Mon, 14 Dec 2015 01:16:48 -0500, rickman Gave us:

Bring it up *to* the rear.

High rpm reciprocating engines have shorter strokes because the dwell time of the explosion is shorter during the combustion cycle. Lower rpm engine have longer strokes because the dwell time of the exploding gas mix has a longer period to exert force in. The longer stroke can only result with a crank which has a longer torque arm distance from center. The result is greater torque per unit force of explosive media.

There is no way around it. Longer stroke translates directly into greater torque throughout the engine's entire operating range.

That is why having a standard 350 chevy "stroked" yielded great gains, and why the casting designers made provisos to allow for said "stroke lengthening. The lifespan suffers, however, which is why it is not done at the factory.

This was back when so much fuel was dumped into each intake cycle that there was a lot of still burning combustion gas left even after bottom dead center was reached. We do not run so rich any more.

This is what I'm talking about, oversimplifying it. Comparing a stroked engine to one that is not stroked is pointless.

If you stroke an engine, yes the torque goes up. If you bore an engine, the torque goes up. In both cases you have increased the displacement. In one you increase the force on the piston which increases the torque, in the other you increase the lever arm the piston has which increases the torque. If the displacement in both cases remains equal, both will have pretty equal torque.

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3.5m/s^2 * ~1700kg = 6000N

wheel radius ~33cm => 2000Nm needed at the wheels ....

-Lasse

I'm not sure what to make of your calculations. The vehicle has the acceleration times it has, and I'm stating the published number for torque. There's no production car in the world that has 1400 foot pounds of torque at the wheels that I'm aware of.

You don't care about where the car's center of gravity is or anything like that in your back of the envelope calculation? Moment of inertia? No?