university final project
TRANSCRIPT
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.
Driver Pulley
Movable
pulley
Piece that
generate
movement
forces
Spring that
affects
engagement
velocity
Baja SAE USB Prototype
CVT = Clutch + Automatic ratio change system
Powertrain = Engine + CVT + Gearbox reduction + Loads
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
0 2 4 6 82000
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 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.