CVT ProjectMATT MYERS, DELANEY BALES, TAYLOR VANDENHOEK, ALEK LINQUIST, JESS MCCAFFERTY

ME 416, FALL 2014

Background CVT - Continuously Variable Transmission

◦ Transitions between an infinite number of gear ratios◦ Primary pulley driven by engine RPM◦ Secondary pulley driven by torque

Baja Team runs a CVT to transfer power from the engine to the gearbox.

How CVT Works

http://grabcad.com/library/cvt-gearbox-1

Purpose The CVT on the Cal Poly Baja car has several factors leading to inefficiencies and improper tuning.◦ Last year we tried tuning the CVT with different weights.◦ Placed 33rd in the Acceleration Event with 5.023 seconds◦ 1st place had a time of 4.199 seconds

CVT should be custom tailored for Baja Car.

This model would be used by the Baja Club to predict CVT performance based on variable inputs.

Goals Our goal as a group was to improve the efficiency of the CVT through theoretical modeling. ◦ Create dynamic model of CVT◦ Determine most influential variables◦ Determine the relationships between variables◦ Reduce time to distance from 0-100 ft and 0-150 ft

◦ Improve acceleration time by 10%, from 5.023s to 4.58s, which would equal 5th place based on 2014 results.

Baja Vehicle Performance Tractive Effort Curve

◦ Ideal Tractive Effort◦ Actual Tractive Effort◦ Road Load◦ Traction Limit

Ideal CVT Ratio

MOTOR CVT GEARBOX CVJ TIRES

η = 96%η = 98%10 HP

η = 85%

3.5-0.9:1 6.25:1Reff = 10in.

0 5 10 15 20 25 30 350

500

1000

1500

2000

2500 TRACTIVE EFFORT

ROAD LOAD

TRACTION LIMIT

IDEAL TRACTIVE EFFORT

ACTUAL TRACTIVE EFFORT

VEHICLE SPEED, MPH

FORC

E, L

BF

0 5 10 15 20 25 30 350.0

1.0

2.0

3.0

4.0

5.0

6.0 IDEAL CVT RATIO

ACTUAL CVT RATIO

IDEAL CVT RATIO

VEHICLE SPEED, MPH

CVT

RATI

O

Theoretical Model SolidWorks model of CVT primary pulley.

Adams simulation of primary pulley to generate the pulley diameter as a function of time and belt tension.

Simulink model to calculate time to distance of the vehicle.

SolidWorks Adams Simulink

Assumptions RPM increases steadily (no longer constant)

Asphalt, no slip

Ignore belt stretching

Constant belt length and width

Constant center-to-center distance between pulleys

Constant effective vehicle mass

SolidWorks CVT primary pulley

Can control ramp angle, weight (material density or volume)

Ramps

70 Degrees 68 Degrees [Flat] 66 Degrees

Θ ΘΘ

WeightsAdjusted mass of 'weights' in Adams

◦ 50 grams◦ 60 grams◦ 70 grams◦ 80 grams

Adams Import SolidWorks model and run primary pulley to generate pulley diameter as a function of time and belt side pressure

Can control:◦ Belt Side Pressure◦ Engine RPM◦ Weights◦ Spring Rate

Results from Adams

0.000 0.500 1.000 1.500 2.0000

500

1000

1500

2000

2500

3000

3500

4000

-0.018

-0.014

-0.009

-0.004

0.000

RESPONSE TIME WITH VARIOUS WEIGHTS

RPM

50 GRAMS

60 GRAMS

70 GRAMS

80 GRAMS

TIME, SECONDS

ENG

INE

SPEE

D, R

PM

PULL

EY D

ISPL

ACE

MEN

T, M

ETER

S

(ramp results)

(Jess will send)

0.000 0.500 1.000 1.500 2.0000

1

1

-0.018

-0.014

-0.009

-0.004

0.000

RESPONSE TIME WITH VARIOUS RAMP ANGLES

RPM

66 DISP

68 DISP

70 DISP

TIME, SECONDS

ENG

INE

SPEE

D, R

PM

PULL

EY D

ISPL

ACEM

ENT,

M

Simulink Calculate time to distance of vehicle, from 0 to 100 ft using Ideal CVT Ratio.

Simulink Calculate time to distance of vehicle, from 0 to 100 ft using Ideal CVT Ratio.

0 1 2 3 4 5 6 7 8 9 100

50

100

150

200

250

300

350

400

0

5

10

15

20

25

30

35

IDEAL CVT RATIO RESULTS

DISTANCE Power (DISTANCE)VELOCITY

TIME, SECONDS

DIS

TAN

CE, F

EET

VEH

ICLE

SPE

ED, M

PH

Summary and Findings◦ Primary does not operate independently from secondary.

◦ Keeps expanding after engine reaches 3400 RPM.◦ Dynamic belt side pressure

◦ From Adams:◦ More weight means faster expansion and quicker response time.◦ Ramp angle has the best chance of obtaining Ideal CVT Ratio◦ Spring stiffness shifts elongates the displacement vs. rpm graph◦ Adams is good for finding trends, but not good for giving realistic data

◦ Model the secondary pulley◦ Experimental results would be better than analytical model results

References Aaen, Olav. Clutch Tuning Handbook. 2007. Print.

Adams Tutorial Kit for Mechanical Engineering Courses. 2nd ed. MSC Software. Print.

Budynas, Richard, and J. Keith Nisbett. Shigley's Mechanical Engineering Design. 9th ed. New York: McGraw-Hill, 2011. Print.

Cha, S.W., W.S. Lim, and C.H. Zheng. "Performance Optimization of CVT for Two-Wheeled Vehicles." International Journal of Automotive Technology 12.3 (2010): 461-68. Print.

Chang-song, Jiang, and Wang Cheng. Computer Modeling of CVT Ratio Control System Based on Matlab. IEEE, 2011. 146-150. Print.

Narita, Yukihito. "Design of Shaft Drive CVT - Calculation of Transmitted Torque and Efficiency." Power Transmission and Gearing Conference. Vol. 5B. ASME, 2005. 875-881. Print.

Willis, Christopher Ryan. A Kinematic Analysis and Design of a Continuously Variable Transmission. Blacksburg, VA: Virginia Polytechnic Institute and State University, 2006. Print.