Gear ratio &

torque-power curves

Captiva Sport 2011 (GM)

LORENA YAMILETH BIGURRA CARRILLO 967683

LUIS FELIPE PACHECO FLORES 968221

ANDREA MUÑOZ LEDO SOTO 1161382

objectives

Obtain torque & power curves experimentally.

Acquire vehicle data using On-Board-Diagnostic

(OBD-II) interface

Use theory of vehicle dynamics in order to

build the curves.

Analize manufacturer curves with experimental curves in

order to see the lost of power due to highness.

analitycal formulation

gxRRdRmaF

Figure 1.1 Free body diagram of forces acting on an inclined vehicle

… (1)

… (2)

considerations

… (3)

… (4)

Technical data

GM Chevrolet Captiva Sport 2011

Gear ratioCHEVROLET CAPTIVA SPORT 2011

6 SPEED AISIN TRANSMISSION

Gearbox ratio

Obtained data through OBD-II interface:

Time (s)

Angular velocity of engine (RPM)

Linear velocity (km/hr)

Wheel radius*:

235/60 R17

Using data of the Wheel we obtainwheel radius: 0.3569 m

*Wheel radius calculated with specifications of the wheel: Fundamentals of Vehicle Dynamics (Gillespie, 1992).

… (5)

… (6)

… (7)

results

ratio* Ntf **

first 5.15 16.65

second 3.38 10.92

third 2.09 6.77

fourth 3.47 11.23

differential*** 3.23

1st, 2nd, 3rd and 4th velocities ratio due to the maximum speed of 61 km/hr.

* Experimental ratio is closer to manufacturer ratio.**Ntf (gear and differential ratio) calculated from (7).***differential ratio from manufacturer data sheet.

Experimental gear ratio Manufacturer gear ratio (6 speed AISIN transmission)

Torque & power

curves

CHEVROLET CAPTIVA SPORT 2011

DOHC 2.4 I-4 ECOTEC ENGINE

General Motors 2.4L DOHC L-4 Curves

(Manufacturer)

Conversion: 1 lb.ft = 1.3558 Nm

Torque curve (lb*ft) & scaled torque curve(N*m)

Power curve(Horse Power)

Curve fitting (experimental)

Data acquisition presents points in which velocity does not change at that

instant of time (velocity constant, no acceleration).

It is necessary to filter constant velocity data in order to avoid peaks which

introduce a high standard deviation.

Original data (manufacturer curve) and the aproximated curve obtained

have a deviation.

For this experiment 6th order polynomial functions are used in order to

represent a better curve of the data: curve fitting.

R2 represents relation between acquired data and curve fitting.

• Darker color = Torque curve by manufacturer• Lighter color = Experimental torque curve with peak points

( v constant, a=0 for that instant of time)

• 6th order polinomial tendency curve adjusting acquired data

Torque engine curveComparative: Manufacturer curve v.s experimental curve

• Lighter color = curve fitting of experimental data neglecting data in which acceleration is nulll

• Experimental curve smoother and similar to manufacturercurve.

y = 1E-10x4 - 6E-07x3 + 0.001x2 - 1.263x + 419.3

R² = 0.804

-50

0

50

100

150

200

250

0 1000 2000 3000 4000 5000 6000 7000 8000

Torq

ue

(N

m)

angular speed (RPM)

y = 1E-10x4 - 5E-07x3 + 0.001x2 - 0.919x + 249.8

R² = 0.180

-50

0

50

100

150

200

250

0 1000 2000 3000 4000 5000 6000 7000 8000

Torq

ue

(N

m)

angular speed (RPM)

Curve with constant velocity points (peaks) Adjusted curve without constant velocity points

Power engine curveComparative: Manufacturer curve v.s experimental curve

y = 5E-11x4 - 3E-07x3 + 0.000x2 - 0.808x + 355.4

R² = 0.836

-50

0

50

100

150

200

0 1000 2000 3000 4000 5000 6000 7000 8000

Po

we

r (H

P)

angular speed (RPM)

• Darker color = manufacturer curve.• Lighter color = experimental curve with oscillating data• 6th order tendency curve fitting of experimental data

Conclusions

Difference between real gear ratio and the calculated ratio of the transmission is mainly due to the average values ofvelocity data acquired.

It is not know the conditions in which the manufacturer curves were tested so that experimental test condition isdifferent.

At the moment of computing torque curve, a peak torque is noticeable around 2500 rpm, it might be caused by thetorque converter of the automatic transmission because it partially modifie the maximum load of the vehicledepending of work requirements.

The most important observation is the engine power loss due to high altitude, it is because there is less pressure and lessoxygen (density of air is different) so that the engine pressure intake drops affecting the power generated bycombustion gases.

Maximum computed power: 129 HP @6700 RPM, 29.1% less power with respect to 189 HP from manufacturerinformation.

Maximum computed torque: 150 Nm @4900 RPM, 37.5% less torque with respect to 250 Nm from manufacturerinformation.

Loss of power is mainly due to high altitude, in less proportion due to transmission efficiency and test conditions arerelated with the behavior of the engine.

Test of engine manufacturers are computed in a dynamo at sea level.

References

Gillespie, T. Fundamentals of Vehicle. USA: SAE, 1992

Norton, R. Design of Machinery. USA: Mc Graw Hill, 2009.

General Motors. 2011 Chevrolet Captiva Sport Owner Manual. USA: 2011

Chevrolet México. Captiva Sport. México: , Web. <http://www.chevrolet.com.mx/>