Shifting Speed and Belt Behavior of Model CVT

(Continuously Variable Transmission) with Push and Pull Type

V-belt Driven on Semi-Transparent Pulleys

Influence of Stiffness of V-belt in Clamping Direction

Shinnosuke Nomura

, Kazuya Okubo

and Toru Fujii

Graduate student of Doshisha University, 1-3 Tataramiyakodani, Kyotanabe-city, 610-0394, Kyoto, Japan

Department of Mechanical Engineering, Doshisha University, 1-3 Tataramiyakodani, Kyotanabe-city,

610-0394, Kyoto, Japan

Keywords: CVT (Continuously Variable Transmission), V-belts, Shifting Speed, Deformation.

Abstract: The purpose of this study is to investigate influence of the stiffness of V-belt in clamping direction on

shifting speed of V-belt type CVT (Continuously Variable Transmission). Model CVT with push and pull

type V-belt was prepared with semi-transparent pulleys made of epoxy resin in order to observe the belt

behaviour in the pulley groove. The stiffness of the belt in clamping direction was changed to investigate

the influence on the shifting speed in which the cross sections of belts were reduced as the alternative types

of belts. At the case where the belt pitch radius was increased, the behaviour of elements of the push type V-

belt in the pulley groove indicated that the remarkable radial slip between the element and pulley was not

occurred. It was suggested that the pitch radius of the belt entering into pulley groove was depended on the

deformation of the belt in compression in clamping direction in pulley groove. It was shown that the shifting

speed was increased by reducing the stiffness of belts in clamping direction regardless of the belt type.

1 INTRODUCTION

The market share of vehicles with V-belt type CVT

is expected to keep growing in the future because

they achieve a higher fuel economy than vehicles

with other transmissions (T.Fujii, 2008). CVTs have

advantages capable of maintaining proper rotational

speed at all time in terms of engine efficiency by

changing speed ratio flexibly and continuously.

An example of V-belt type CVT setup is shown

in Figure 1. The V-belt type CVT is composed of a

driving V-pulley, a driven V-pulley and a V-belt.

These V-belts are classified into two types, push

type V-belt and pull type V-belt. The driving V-

pulley and the driven V-pulley both are usually

composed of a movable pulley and a fixed pulley.

The V-belts are clamped between the movable

pulley and the fixed pulley in order to generate

traction by frictional force. Clamping force is

usually applied onto belt by oil pressure generated

by oil pump and others. On changing balance of

clamping forces between the driving movable

V-pulley and the driven movable V-pulley, the shift

change sets in.

Figure 1: V-belt type CVT setup.

To keep safety operation and provide practical

shifting speed clamping force is often excessive over

the reasonable force. Oil pump loss for applying

clamping force onto belt often accounts for approxi-

474

Nomura, S., Okubo, K. and Fujii, T.

Shifting Speed and Belt Behavior of Model CVT (Continuously Variable Transmission) with Push and Pull Type V-belt Driven on Semi-Transparent Pulleys.

DOI: 10.5220/0006781604740480

In Proceedings of the 4th International Conference on Vehicle Technology and Intelligent Transport Systems (VEHITS 2018), pages 474-480

ISBN: 978-989-758-293-6

mately 60% of loss in the whole CVT units. Therefore,

the clamping force should be reduced to increase

efficiencies of CVTs. The motivation of the work is to

develop new CVT with high efficiencies and response.

The purpose of this study is to investigate the

influence of stiffness of V-belt in clamping direction

on shifting speed of V-belt type CVT in order to

discuss the mechanical design to determine

appropriate clamping force.

2 TEST METHOD

2.1 Test Setup

The model CVT was developed with light V-belt

and semi-transparent epoxy resin pulleys in which

the belt behaviour in pulley groove was able to be

observed. Figure 2(a)(b) shows the illustration of

model CVT test apparatus used for measurements.

(a) Top view

(b) Front view around driven pulley

Figure 2: Schematic view of test apparatus of model CVT.

The test apparatus was set up with the model CVT

unit, the A/C motor, the winch, and the lever. The

A/C motor was installed instead of a combustion

engine to provide power. The power was transmitted

to the driven shaft from the driving shaft through the

CVT unit. Driven torque was applied by winding up

a weight by a wire on the shaft. Pulley clamping

force was also applied onto belt by another weight

with levers instead of oil pressure.

2.2 Specimens for Measurements

Pushing type model belts were originally prepared

with tentative elements made of acrylic resin and

laminated steel rings. Low-stiff push type belts with

low-stiff elements were also prepared of which cross

sections of the elements were reduced by

introducing a flat notch to change the stiffness in

clamping direction (Figure 3). For the alternative

push type belt, stiffness of the belt was reduced

about 30% in clamping direction compared with that

of the original belt.

Figure 3: Elements of push type belts.

Pulling type model belts were also prepared

made of rubber elastomer and steel cords. Low-stiff

pull type belts were also prepared of which cross

sections of the belt were reduced by introducing a

half circular notch to change the stiffness in

clamping direction (Figure 4). For the alternative

pull type belt, stiffness of the belt was reduced about

31% in clamping direction compared with that of the

original belt.

Figure 4: Cross sections of pull type belts.

Shifting Speed and Belt Behavior of Model CVT (Continuously Variable Transmission) with Push and Pull Type V-belt Driven on

Semi-Transparent Pulleys

475

2.3 Measurement of Shifting Speed

The speed ratio i was defined as the equation (1).

i ==

(1)

where, R

, R

, N

denoted the pitch radius

of belt in the driving pulley and in the driven pulley,

the rotational speed of the driving shaft and of the

driven shaft, respectively.

Table 1 and 2 shows test conditions for push and

pull type, respectively. The shifting speed was

defined as dR/dt (the variation of belt pith radius per

unit of time).

Table 1: Test conditions with push type belt.

Table 2: Test conditions with pull type belt.

The rotational speed of the driving pulley was about

20rpm during experiments. The transmitted torque

was also kept constant at 294Nmm. The shifting

speed was evaluated by measuring the times

required for the belt to change to change the pitch

radius associated with i=1.25 to i=0.8 for shifting up

and opposite change to shifting down, respectively

(Figure 5).

Figure 5: Measurement of shifting speed.

2.4 Measurements of Radial Slip

Figure 6 shows an example of the result of image

analysis. To evaluate radial slip between elements in

pulley groove and pulley, the behaviour of an

element of push type belt in pulley groove was

observed by a miniature camera attached onto driven

pulley. The radial displacement of the point mark

attached on contact surface of the element from

initial point was measured as radial slip between

element in pulley groove and pulley.

Figure 6: Example of result of image analysis.

3 RESULTS

Figure 7(a)(b) and Figure 8(a)(b) show the

relationship between the shifting speed and

clamping force measured with the push type low-

stiff belt and the conventional belt. The significant

Shift up state

(

i = 1.25

→

0.8

)

Shift down state

(

i = 0.8

→

1.25

)

Rotational speed of

drivin

ulle

Transmitted torque

Clamping force of

drivin

ulle

186, 206, 225, 245, 265N 147N

Clamping force of

driven

ulle

147N 186, 206, 225, 245, 265N

20rpm

294Nmm

Shift up state

(

i = 1.25

→

0.8

)

Shift down state

(

i = 0.8

→

1.25

)

Rotational speed of

drivin

ulle

Transmitted torque

Clamping force of

drivin

ulle

186, 206, 225N 118N

Clamping force of

driven

ulle

118N 186, 206, 225N

20rpm

294Nmm

VEHITS 2018 - 4th International Conference on Vehicle Technology and Intelligent Transport Systems

476

difference was observed in the shifting speed of the

push type low-stiff belt and that of the push type

conventional belt.

These results showed that reducing the stiffness

of belt elements in clamping direction contributed to

increase the shifting speed.

(a) Under shifting up

(b) Under shifting down

Figure 7: Relationship between shifting speed and

clamping force in push type belt when transmitted torque

was almost zero.

(a) Under shifting up

(b) Under shifting down

Figure 8: Relationship between shifting speed and

clamping force in push type belt when transmitted torque

was 294[Nmm].

Figure 9(a)(b) and Figure 10(a)(b) show the

relationship between the shifting speed and

clamping force measured with the pull type low-stiff

belt and the conventional belt. The significant

difference was also observed in the shifting speed of

the pull type low-stiff belt and that of the pull type

conventional belt.

These results showed that reducing the stiffness

of belt in clamping direction contributed to

increasing the shifting speed, as well as the test

results with push type belts.

Shifting Speed and Belt Behavior of Model CVT (Continuously Variable Transmission) with Push and Pull Type V-belt Driven on

Semi-Transparent Pulleys

477

(a) Under shifting up

(b) Under shifting down

Figure 9: Relationship between shifting speed and

clamping force in pull type belt when transmitted torque

was almost zero

(a) Under shifting up

(b) Under shifting down

Figure 10: Relationship between shifting speed and

clamping force in pull type belt when transmitted torque

was 294[Nmm].

4 DISCUSSIONS

Figure 11 shows the radial slip between element and

pulley at the case where the belt pitch radius was

decreased and that at the case where the belt pitch

radius was increased, respectively. At the case where

the belt pitch radius was decreased, radial slip

between element and pulley was remarkably

occurred. On the other hand, at the case where the

belt pitch radius was increased, radial slip was

VEHITS 2018 - 4th International Conference on Vehicle Technology and Intelligent Transport Systems

478

almost not observed even if shifting state. It was

suggested that the belt pitch radius was increased not

by slipping between element and pulley but by

deformations of elements in clamping direction.

Figure 11: Radial slips between element and pulley for

push type belt.

Figure 12(a)(b) and Figure 13(a)(b) show the

behaviour of push type belt and pull type belt in

pulley groove at the case where the belt pitch radius

was increased and that at the case where the belt

pitch radius was decreased. Same tendencies were

observed on the belt behaviours for push type and

pull type belt, as bellow. The belt pitch radius was

decreased maintaining complete circle shape by

which the belt significantly slipped in pulley groove

in the same time (Figure 12(b) and 13(b)). On the

other hand, the belt pitch radius was increased as

spiral shape by some deformations of the belt in

clamping direction in the pulley groove without

significant slip (Figure 12(a) and 13(a)).

The belt was deformed in compression in pulley

groove by clamping force. At the case where the belt

pitch radius was increased, the belt entering into

pulley groove should be entered at external position

in radial direction because internal sheer force was

produced by the difference of the radial locations

around the entrance. The difference of the radial

locations was increased when large deformation of

the belt was occurred with low-stiff belt in clamping

direction. Therefore, the pitch radius of the belt

entering into pulley groove was depended on the

deformation of the belt in pulley groove.

That is reason why reducing the stiffness of belt

in clamping direction contributed to increase the

shifting speed. This study showed that the shifting

speed of CVT was improved when the stiffness of

belt was reduced in clamping direction regardless of

the belt type.

(a) In case of increasing of belt pitch radius

(b) In case of decreasing of belt pitch radius

Figure 12: Behaviours of push type belt in pulley groove

Shifting Speed and Belt Behavior of Model CVT (Continuously Variable Transmission) with Push and Pull Type V-belt Driven on

Semi-Transparent Pulleys

479

(a) In case of increasing of belt pitch radius

(b) In case of decreasing of belt pitch radius

Figure 13: Behaviours of pull type belt in pulley groove.

5 FUTURE WORK

We are expecting these results should be applied to

actual CVT with the metal V-belt and pulleys. To do

this, we will evaluate appropriate dimensions such

as the shape and material of belt.

6 CONCLUSIONS

This study investigated influence of the stiffness of

V-belt in clamping direction on shifting speed of V-

belt type CVT by observing the belt behaviour in

pulley groove with semi-transparent pulleys. These

conclusions were obtained as follow.

(1) At the case where the belt pitch radius was

increased, the behaviour of belt elements in the

pulley groove indicated that the remarkable

radial slip between belt element and pulley was

not occurred.

(2) The pitch radius of the belt entering into pulley

groove was depended on the deformation of the

belt in compression in clamping direction in

pulley groove.

(3) The shifting speed of CVT was improved when

the stiffness of belt was reduced in clamping

direction regardless of the belt type.

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