How to draw transmission curves for gearbox

waiting for replay...
help appreciated

I might be able to help, Classic perfromance table:

Left Y axis scale off for tractive effort (driving force) and running resistance in kg (kn if you are so disposed)
Right Y axis scale off for engine rpm (note the two Y axis' do not relate to one another.

x axis scale for vehicle speed kph

1. Plot vehicle speed versus tractive effort curves for each gear.

TE = engine torque * final drive ratio/rr

rr = rolling radius

The peaks on these curves are the maximum tractive effort point.

Draw a system tractive effort curve by using the outer tangents of each gear curve. This curve should be a smooth arc starting steep (high effort) at the short gear and shallowing out (low effort) on the longest gear (highest speed).

2. Plot rpm verus vehicle speed curves

0.377* rr * rpm/fdr
rr = rolling radius of driven wheel
fdr = final drive ratio (drive gear * rear axle ratio)

The vertical intercepts of lines drawn though these curves gives you an idea of the maginitude of loss in torque as you change down, or gain as you change up. Big magnitudes result in poor behaviour.

Gear selection should be based on maximum engine speed and maximum engine torque speed. Changing up form maximum engine speed should always result in engine speed greater than max engine torque speed.

3 Plot running resistance % curves. These are the sum of grade resistance, air resistance and rolling resistance in kg. These indicate the gradability of the vehicle e.g how it will take on hills, etc.

Running resistance is independent of the gears


Where the running resisitance 0% curve intersects the longest gear is the max speed.

Thanks man, I almost gave up this one
THX