Done by:

Reinaldo Alexander Wiener Rocca

Academic tutor: Prof. Sergio Díaz

General objective

Create a numerical simulation that allows to change the most important parameters of the CVT, to study the influence of each one, in the dynamic performance, under different track conditions.

Specific Objectives

Disassembly a CVT CVTech IBCTM brand Model # 0600-0021 / 5600-0171 to understand the internal physical reactions and to obtain the equation of motion of the system.

Obtain a model of vehicle’s motion that simulates the process of clutching and ratio change during movement, contemplating various track conditions.

Validate the model by comparing with experimental measurements on the prototype USB Baja SAE 2010.

Specific Objectives

To study the influence of CVT ‘s parameters, the final drive ratio and other important parameters; in different output variables such as engine speed, vehicle speed, acceleration, distance traveled, among others.

Establish a methodology for selection of transmission ratio(s) of the final gear reduction of the prototype.

Establish a methodology for selecting optimal parameters in the CVT, to improve prototype’s performance.

Belt-CVT Transmit power from the

driving shaft to driven shaft offering different gear ratio values and maintaining engine speed constant.

Ratio changes are sequential and infinite within a range and are made automatically.

Each pulley has a movable semi-pulley to enable ratio changes.

Mini-Baja prototype’s CVT behaviour

Vehicle’s Dynamics model

Driver Pulley

Movable

pulley

Piece that

generate

movement

forces

Spring that

affects

engagement

velocity

Diven Pulley

Movable

pulley

Spring that

resist to ratio

change

CVT’s Parameters

Baja SAE USB Prototype

CVT = Clutch + Automatic ratio change system

Powertrain = Engine + CVT + Gearbox reduction + Loads

Experimental Validation of the model

Model results

Experimental test (Left) vs. Simulated results (Right)

0 2 4 6 82000

2200

2400

2600

2800

3000

3200

3400

3600

3800

4000A.

tiempo (s)

Vel

ocid

ad d

el m

otor

(R

PM

)

C1

C2

C3

C4

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2200

2400

2600

2800

3000

3200

3400

3600

3800

4000B.

tiempo (s)

Vel

ocid

ad d

el m

otor

(R

PM

)

C1

C2

C3

C4

0 2 4 6 80

5

10

15

20

25

30

35

40A.

tiempo (s)

Vel

ocid

ad d

el c

arro

(km

/h)

C1

C2

C3

C4

0 2 4 6 80

5

10

15

20

25

30

35

40B.

tiempo (s)

Vel

ocid

ad d

el c

arro

(km

/h)

C1

C2

C3

C4

Influence of CVT’s parameters (Fsh1 – inductive force on driver pulley)

0 2 4 6 8 10 120

1

2

3

4

5

6

7A.

velocidad del carro (m/s)

ace

lera

ción d

el c

arr

o (

m/s

2)

150

190

230

270

310

350

390

430

0 2 4 6 8 10 121500

2000

2500

3000

3500

4000B.

velocidad del carro (m/s)

velo

cidad a

ngula

r del m

oto

r (R

PM

)

150

190

230

270

310

350

390

430

0 2 4 6 8 10 12 140

50

100

150A.

tiempo (s)

dist

anci

a re

corr

ida

(m)

150

190

230

270

310

350

390

430

0 5 10 150

2

4

6

8

10

12B.

tiempo (s)

velo

cida

d de

l car

ro (

m/s

)

150

190

230

270

310

350

390

430

Acce

lera

tion

Dis

tance

Engin

e’s

speed

Vehic

le’s

speed

Influence of CVT’s parameters (Fsh1 – inductive force on driver pulley)

Inductive force directly affects the engine speed

Inductive force increases the transmitted force (acceleration).

For higher centrifugal-weight a lower engagement speed will be obtained, hence stiffer spring must be used to maintain this parameter within the desired range.

Influence of CVT’s parameters (Fsh2 – resistive force)

0 2 4 6 8 10 120

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5A.

velocidad del carro (m/s)

acele

ració

n d

el carr

o (

m/s

2)

90

120

150

180

210

240

270

0 2 4 6 8 10 122200

2400

2600

2800

3000

3200

3400

3600

3800B.

velocidad del carro (m/s)

velo

cid

ad a

ngula

r del m

oto

r (R

PM

)

90

120

150

180

210

240

270

0 2 4 6 8 100

10

20

30

40

50

60

70

80

90

100A.

tiempo (s)

dis

tanci

a r

eco

rrid

a (

m)

90

120

150

180

210

240

270

0 2 4 6 8 100

2

4

6

8

10

12B.

tiempo (s)

velo

cidad d

el c

arr

o (

m/s

)

90

120

150

180

210

240

270

Accele

ration

Dis

tance

Engin

e’s

speed

Vehic

le’s

speed

Influence of CVT’s parameters (Fsh2 – resistive force on driven pulley)

Influences directly in the clutching/engagement time.

Have influence on the top speed.

Generates different effects comparing to inductive forces.

Influence of Vehicle’s Parameters (Gearbox ratio)

0 5 10 150

1

2

3

4

5

6

7A.

velocidad del carro (m/s)

acele

ració

n d

el carr

o (

m/s

2)

8

10

12

14

16

18

20

22

24

0 5 10 152200

2400

2600

2800

3000

3200

3400

3600

3800B.

velocidad del carro (m/s)

velo

cid

ad a

ngula

r del m

oto

r (R

PM

)

8

10

12

14

16

18

20

22

24

Accele

ration

Engin

e’s

speed

Gearbox ratio computation (design parameter)

Methodology to optimize CVT’s performance

Gearbox ratio computation Knowing the top speed

vc (m/s) d (m)

9 20

10 25

11 30

12 45

13 70

14 120

15 160

Load

curve

Gearbox ratio selection

The optimal value is one that delivers maximum acceleration without sacrificing the top speed of the vehicle or the value which delivers maximum energy in a fixed distance.

Once top speed is obtained, kinematical relationship is used to estimated the necessary gearbox ratio.

Optimization of CVT’s performance

Maximizing the tension during clutching (taking advantage of the slip energy).

Keep engine operating within the range of maximum power.

Keep CVT uncoupled at engine’s idle speed.

Upper limits (Efficiency and structural damage) are not covered in this work.

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

8,00

9,00

1500,00 2000,00 2500,00 3000,00 3500,00 4000,00

Po

ten

cia

(H

P)

Velocidad del motor (RPM)

Engine Power

Step 1: Find the optimal engine speed (engine curve)

Paso 2: Adjust parameters to obtain a high inductive force, being careful to remain engine uncoupled at idle speed.

Paso 3: Adjust parameters on driven pulley to balance inductive force and to achieve desired engine speed.

0 5 10 150

1

2

3

4

5

6

7A.

velocidad del carro (m/s)

ace

lera

ción d

el c

arr

o (

m/s

2)

P1

P3

P5

P7

0 5 10 151500

2000

2500

3000

3500

4000

X: 11.6

Y: 3281

B.

velocidad del carro (m/s)

velo

cidad a

ngula

r del m

oto

r (R

PM

)

P1

P3

P5

P7

Optimization of CVT’s performance

Conclusions The model fulfills the objectives satisfactorily.

It was observed that the slip during clutching is common and also beneficial in applications with low power engines. This is because that kinematical energy from engine is higher that engine’s power (10 HP) at uncoupled stage.

Estimated values of the internal forces are obtained. This values is useful to design the inlet shaft of the gearbox.

It was possible to establish a methodology to select the final drive ratio and the optimal parameters of the CVT.

Recommendations Find a way to measure also change of position of semi-

pulleys on driver and driven pulley, to know exactly when change of ratio start and stop.

Include in the model the variation of efficiency in terms of the belt tension.

Develop a model that describes accurately the creep that occurs in the belt-pulley contact during ratio change.

Perform a test bench were inlet torque and load torque can be controlled and measured to reduce errors.