flat4 - driving
|Driving performance calculations at the example
of the 1.2 liter engine
Engine power and torque diagrams
Diagramm of tractive forces
These are the input values of the calculation program:
|Technical data VW 1200 25kW (34bhp)
|cd drag coeff.
|rolling resistance coeff.
|tyre rolling radius
|const. drivetrain loss
|gear ratio 1st gear
|gear ratio 2nd gear
|gear ratio 3rd gear
|gear ratio 4th gear
|Max. engine power
||25 kW (34bhp)
|Max. engine torque
|Max. engine revs
With these input values the 1200cc bug achieves a top
speed of 115 km/h and an acceleration from 0 to 100 km/h of 32 sec.
|Engine power and torque diagrams
Power and torque curves of the 1.2 liter 25 kW (34 bhp)
and 1.6 liter 37 kW (50 bhp) engines. Triebwerks eingezeichnet.
The maximum revs of the 1.6 liter engine increased from 4100 to 4600 1/min
(+12%), torque increased about 33% due to the greater displacement. Because
of the dual pipe intake manifold power increased about 47%. Further calculations
are made on the basis of the 1.2 liter flat4 engine.
This diagram shows the tractive wheel force versus vehicle
speed depending on the actusl gear and the uphill gradient. If the gradient
is zero the green line shows the rolling tyre force (constant value) and
the blue line shows the drag force which is increasing with speed. At the
intersection of the blue line and the red line of the 4th gear the 1200cc
beetle reaches its top speed of 115 km/h. At this point the full engine
power is needed to keep the top speed - no further acceleration is possible.
|Tractive force diagram (VW 1200 25kW/34bhp)
In the third gear it is possible to climb a 10% slope
between 30 and 60 km/h. The offered tractive force is higher than the demand
(10% line). Below 30 km/h the 2nd gear has to be taken which enables the
driver to climb an uphill gradient up to 20%.
All speeds from stillstand to the beginning of the red
curves must be driven with the help of the slipping clutch.
The vehicle acceleration versus vehicle speed gives a comparison
value between different vehicle concepts with different curb weights, engine
torques and gear ratios. What I mean is that the values of power and torque,
taken from brochures, don't give sufficient informations about the real
driving (and acceleration-) performances..
|Acceleration diagram (VW 1200 25kW/34bhp)
The VW 1200 acheives in the first gear at 15 km/h a maximum
acceleration of 3 m/s² (about 30% of the earth gravity). In the 4th
gear at 115 km/h (top speed) there is no further acceleration possible.
If the driver wants to accelerate from 45 km/h with max.
acceleration, e.g. when leaving a city speed limit, he can do that in the
2nd, 3rd or 4th gear. In the 3rd gear a 50 higher acceleration is possible
than in the 4th. In the second gear even twice of the acceleration of the
4th gear is possible. However the driver has to shift in the 3rd at 50
km/h and the acceleration will soon decrease
In real life changes in engine power, drag ceofficient
and rolling tyre resistance must be taken into consideration. All the calculated
forces and accelerations might change when the curb weight increases due
to heavy options.
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