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Journal of Advanced Mechanical Design,Systems, andManufacturing

Vol. 6, No. 2, 2012

236

Development of a Smart Bicycle

Based on a Hydrostatic Automatic Transmission*

Dinh Quang TRUONG**, Kyoung Kwan AHN**,

Le Duy KHOA*** and Do Hoang THINH***** School of Mechanical Engineering

Daehakro 93, Namgu, Ulsan 680-749, Korea

E-mail: [email protected]

*** Graduate School of Mechanical and Automotive Engineering

Abstract

This paper develops a newly bicycle concept named smart bicycle (SBIC) with

automatic transmission and energy recuperating ability. The SBIC operation is

based on a hydrostatic transmission (HST). Several HST designs have been

proposed. Moreover, a use of energy converting and storing devices is an optional

design for the SBIC to recovery energy during the deceleration or going downhill

process, and to support this energy to the hydraulic system during the acceleration

or going uphill process. The working efficiency of the bicycle is then increased and

could become competitive with the roller-chain technology. Simulations have been

carried out to evaluate the working performances of the proposed SBIC concepts.

Key words: Bicycle, Automatic, Hydrostatic Transmission, Energy, Recovery

1. Introduction

Nowadays, hydraulic systems have been considered as potential choices for modernindustries ranging from heavy-duty manipulators to precision machine tools. In bicycle

design, there are many attempts to replace the classic chain transmission with hydraulic

transmissions for a higher durability and a continuousness in changing speed levels.

In the traditional bicycles, standard chains suffer from a multitude of problems such as

working environment or un-desirable tendency to slip off the sprockets. On the other hand,

a hydraulic bicycle could be entirely enclosed, consequently, preventing un-wanted

contaminants from contacting with the mechanical elements. By using hydraulics, the

power is transmitted into the rear wheel via a working fluid traveling through narrow

tubing. This tubing could be mounted on the bicycle frame greatly reducing the possibility

of a disconnection. However, most of studies for a bicycle based on hydraulic transmission

in the literatures only achieved working efficiencies lower than 80%

(1)

. Meanwhile, it isknown that by using classic chain-drives, bicycle designs can reach efficiencies well above

90%(2, 3)

. The reason is due to the reliance on conventional hydraulic technology in which

the losses through all components, especially from valves, are remarkable.

In order to overcome the above restriction of the hydraulic bicycles, this paper is to

develop a newly concept for a hydraulic bicycle with automatic transmission and energy

recuperating ability which is named smart bicycle. The SBIC operation is based on a

hydrostatic transmission. Several HST designs for the bicycle have been proposed.

Moreover, a use of energy converting and storing devices is an optional design for the

bicycle. This design is to recovery the energy during the deceleration or going downhill

process and then to support this energy amount to the hydraulic system during the

acceleration or going uphill process. As the result, the working efficiency of the bicycle isincreased. The overall transmission efficiency in this design could theoretically become

competitive with the roller-chain technology.

*Received 6 Nov., 2011 (No. 11-0678)[DOI: 10.1299/jamdsm.6.236]

Copyright 2012 by JSME


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2. Smart Bicycle Design

2.1. Smart bicycle concepts

Pump-controlled systems are defined as hydraulic systems where speed of the end

effect is directly controlled by the pump(4, 5)

. For rotary loads, pump-controlled systems are

well known as hydrostatic transmissions (HST) including open-loop and closed-loop

circuits. Advantages of open-loop HST over closed-loop HST are simple and capacity ofheat dissipating. On the other hand, the use of closed-loop HST can reduce size and oil

volume and increase bandwidth of the system(6)

. Hence, the closed-loop HST is proposed to

be applied to the bicycle for an automatic transmission with high efficiency. In SBIC design

process, the regenerative braking system also should be considered, especially in case of

going downhill. In the traditional bicycle design, the rider applies a braking force during the

time of going downhill in order to keep the moving speed in a proper range with safety.

Most of kinetic energy is then wasted and converted into heat. Therefore, it is necessary to

find out a solution to regenerate this energy which can be used to combine with the rider

power for moving the bicycle in acceleration time or uphill time.

From the above analysis, to design the novel SBIC, two main targets are defined as:

An automatic transmission in the bicycle; A possibility of recovering energy during decelerations or going downhill by applying

braking actions, and supporting this energy again for accelerations or going uphill.

Here, the bicycle input power is depended on the rider. Therefore, to enhance the first

target, the closed-loop HST control system must be designed with main components as:

A variable displacement bi-directional hydraulic pump: is used to convert from

mechanical power created by the rider to hydraulic power;

A fixed displacement bi-directional hydraulic motor: is used to convert from hydraulic

power to mechanical power which creates the rotation of the rear wheel, consequently,

creating forward movement for the bicycle;

A proportional four ports-two positions control valve: functions as a controllable

hydraulic brake. Advantages of using this brake are:+ Enclosed-brake: it can be protected itself from bad environment effects, such as dirt.

+ Powerful brake: can handle very high loads without requiring the rider to apply a large

force on the hand-brake.

Two transmission gear boxes: are suggested to be used. Here, a gear box is connected

from the crank shaft to the hydraulic pump in order to convert from a low rider speed to

a high rotating speed of the pump. On the other side, the hydraulic motor produces a

high speed while the rear wheel speed is quite low. Therefore, the other gear box is

needed to connect from the motor output shaft to the rear wheel shaft. Furthermore, by

using the gear boxes, the hydraulic pump and motor can be selected with small sizes

which are suitable to install into the bicycle;

An angular speed sensor and a torque transducer: are used to measure the rider speedand the HST output torque, respectively. Therefore, the speed sensor is attached to the

crank mechanism while the torque transducer is attached to the output shaft of the motor.

The sensor feedback signals are then used to manage the automatic transmission mode;

A main control unit (MCU): is used to enhance the automatic transmission. In the

automatic control mode, the MCU receives the sensor signals, consequently, adjusting

the pump swash plate angle. As the result, the bicycle speed is automatically controlled

with respect to the apply power from the rider and road profiles.

Others: a small reservoir, hydraulic pipelines, pressure relief valves

Figure 1. Schematic diagram of proposed HST for the SBIC


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Based on the main HST components, the structure of the SBIC transmission system is

suggested as displayed in Fig. 1. Several SBIC designs have been then proposed to

investigate the working performances and to find out the best design solution.

2.1.1. Concept 01 SBIC01 based on a closed-loop HST without regenerating energy

In this concept, the HST is built to enhance only the first design target automatic

transmission. From the derived transmission diagram in Fig. 1, the first SBIC concept iscalled SBIC01 and proposed as in Fig. 2. As seen in this figure, there are two decisive

components which directly affect to the performance of the bicycle: the hydraulic pump and

proportional control valve. Here, the pump displacement is determined by the swash angle

which can be varied by the MCU automatic control mode or by the rider manual control

mode. The proportional control valve is employed to adjust the flow rate outing from the

motor during a braking process. The port open areas are adjusted by a control signal of the

solenoid which is given by the MCU or by the rider. Besides using the hydraulic brake, the

traditional drum brake is still remained in the SBIC01 as an added option for the rider when

the bicycle drops into emergency cases such as going downhill with high speed.

1. Pedal-Crank 8. Proportional 4/2 Control Valve Hydraulic Brake

2. Angular Speed Sensor 9. Fixed Disp. Bi-directional Hydraulic Motor

3. Gear Box 01 10. Torque Transducer

4. Variable Disp. Bi-directional Hydraulic Pump 11. Gear Box 02

5. Check Valves 12. Drum Brake

6. Reservoir 13. Rear Wheel7. Pressure Relief Valves

Figure 2. SBIC Design concept 01 SBIC01

1. Pedal-Crank 9. Fixed Disp. Bi-directional Hydraulic Motor

2. Angular Speed Sensor 10. Torque Transducer3. Gear Box 01 11. Gear Box 02

4. Variable Disp. Bi-directional Hydraulic Pump 12. Electric Motor / Generator

5. Check Valves 13. Batter

6. Reservoir 14. Rear Wheel

7. Pressure Relief Valves 15. Drum Brake

8. Proportional 4/2 Control Valve Brake 16. Clutches


2.1.2. Concept 02 SBIC02 based on a closed-loop HST with regenerating energy

From the demands for an automatic transmission as well as a regenerative braking

system, the second design idea for the SBIC is named SBIC02 and displayed in Fig. 3. In

this design concept, it can be seen that the HST mechanism is almost similar as in the first

design SBIC01. There is only one different thing in the SBIC02 that is a regenerative part.The regenerative circuit is installed besides the drum brake. This circuit includes an electric


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motor/generator and a compatible electric battery. In addition, there are three clutches are

positioned between: the 1stgear box and hydraulic pump; the 2

ndgear box output shaft of

the hydraulic motor and electric motor/generator; the 2nd

gear box and rear wheel shaft.

During the braking phase, the regenerative circuit is activated. The kinetic energy of the

bicycle is partially recovered by the electric motor/generator (at this time, it functions as a

generator) and stored in the battery. On the contrary, in the normal operation, the energy inthe battery is combined with the rider power to supply the pump control mechanism about

torque and speed for system acceleration or going uphill (at this time, the electric

motor/generator functions as a motor). Furthermore, the battery energy is also used to

supply for the main control unit and other electric devices in the bicycle.

1. Pedal-Crank 9. Fixed Disp. Bi-directional Hydraulic Motor

2. Angular Speed Sensor 10. Torque Transducer

3. Gear Box 01 11. Gear Box 02

4. Variable Disp. Bi-directionalHydraulic Pump 12. Electric Generator

5. Check Valves 13. Battery

6. Reservoir 14. Rear Wheel

7. Pressure Relief Valves 15. Drum Brake

8. Proportional 4/2 Control Valve Hydraulic Brake 16. Electric Motor

17. Clutches


2.1.3. Concept 03 SBIC03 based on a closed-loop HST with regenerating energyAs the analysis in 2.1.2, the regenerative circuit is necessary in bicycle design for

energy saving purpose. Another design solution for the SBIC enhancing this target is

derived as SBIC03 and depicted in Fig. 4. In this SBIC03, the electric generator and the

electric motor are separated instead of combining together as in the SBIC02. Therefore, the

working principle of the SBIC03 is the same as that of the SBIC02. Advantages and

disadvantages of the two regenerative circuits in these designs can be shown in Table 1.

Table 1. Basic comparison between the regenerative circuits in SBIC02 and SBIC03

Characteristics Integrated Electric Motor-Generator Separated Electric Motor-Generator

Size Compacted component Two components

Install More difficult Easier for distributive installation

Controllability More difficult Easier to manage and controlTable 2. SBIC design constraints

Constraints Values Units

Maximum power of a rider Pr_max 0.5 (0.65) kW (hp)

Maximum weight of the rider Mr_max 75 kg

Weight of bike and equipped devices Mbike 25 kg

Maximum rotational speed of pedal-crank ncrank 90 rpm

Maximum speed of the bicycle vbike 32 km/h

Gear ratios are within a range R1, R2 1:10 to 1:20

Diameter of the wheel Dw 0.6858 m

Overall efficiency of hydraulic motor and pump p m 0.92

Efficiency of gear transmission G 0.96


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2.2. Basic hydrostatic transmission design for the proposed SBIC (SBIC01)

2.2.1. HST design specifications

Firstly, all constraints to design the HST for the bicycle can be listed up in Table 2. To

calculate the required torque, road conditions need to be defined as:

Road surface: Asphalt Concrete;

Rolling resistance:Rr= 17/1000, for the type of bicycle tires on concrete; Maximum grade (slope) of road:Rg= 12 %.

Next, the bicycle must be designed to satisfy following criteria:

The bicycle must be able to reach an acceleration of a= 1.1 m/s2(= 3.21 rad/s2);

To select the HST drive with the hydraulic pump and motor specifications to ensure:

+ Maximum of working pump flow, and maximum of working torque to spin the rear;

+ Possibility to be installed on the bicycle frame while the working performance and the

safety conditions (such as stress, deformation, etc) are guaranteed.

2.2.2. Force and torque analysis for the bicycle design

It is well-known that bicycles handle best when 55 % of the total bicycle and rider

weight is on the rear wheel while 45 % is on the front wheel(7)

. From 2.2.1, the total

weight of the bicycle and rider is_ max

100total r bike

M M M= + = kg (1)

The reaction force at the rear wheel is

0.55 100 9.81 0.55 550rw total F M g= = N (2)

a) Maximum torque required to spin the rear wheel

550 0.5 0.343 94.325s rw wT F r= = = Nm (3)

where: is a coefficient of friction between the wheel tire and the road surface. It is

assumed 0.5 for dry asphalt and rubber;wr is the rear wheel radius.

b) Desired torque to move the bicycle

Assumed that the bicycle is able to accelerate with a= 1.1 m/s2. Therefore, the force

needed to generate that accelerator can be computed as

100 1.1 100a total F M a= = = N (4)

From Eqs. (1), (4), and the road conditions, the total force at the rear wheel to move the

bicycle with the maximum grade of 12% is

( ) ( )_ 100 9.81 0.017 0.12 110 247rw total total r g aF M g R R F= + + = + + N (5)The total torque at the rear wheel is then obtained as

_247 0.343 84.721

w rw total wT F r= = = N (6)

Equations (3) and (6) show s wT T> means the bicycle is able to develop sufficient

traction before the wheel slip to climb the maximum grade with acceleration of 1.1 m/s2.

2.2.3. Calculation for the HST design

In order to design and select the suitable hydraulic pump and motor for the HST, the

maximum operating pressure is considered with:

max 100p p = bar (7)

By the trial method, ratios for the gear boxes 01 and 02 (see Figs. 1 and 2) are selected

( )

( )1

2

1: 20 frompedal-crank tohydraulicpump

15: 1 fromhydraulic motor torear wheel

R

R

=

= (8)

a) Hydraulic motor calculation

From Eq. (3), the required maximum torque at the hydraulic motor shaft is obtained

,max2

94.3256.288

15

sm

TT

R= = Nm (9)

Maximum displacement of the motor is then derived as

6,max,max 5

2 2 3.14 6.288 10 3.951100 10

mm

TDp

= =

cc/rev (10)


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Because the maximum velocity of the bicycle is 32 km/h (Table 2), the angular speed of

the wheel to enhance this bicycle velocity is computed

30 32 30247.47

3.6 0.343 3.6 3.14

bikew

w

vn

r

= =

rpm (11)

From Eqs. (8) and (11), the maximum angular speed of the hydraulic motor is given

,max 2 247.47 15 3713m wn n R= = rpm (12)Maximum flow rate via the hydraulic motor is then obtained as

,max ,max,max

3.951 371314.66

1000 1000

m mm

D nQ

= = lpm (13)

b) Hydraulic pump calculation

From Eq. (13), the required flow rate which is supplied by the pump is

,max,max

14.6615.934

0.92

mp

m

QQ

= = lpm (14)

The theoretical flow rated supplied from the pump is calculated

,max

,max

15.93417.32

0.92

p

tp

p

QQ

= = lpm (15)

From Table 2 and Eq. (8), the maximum speed of the pedal-crank and the gear ratio of

the 1stgear box are 90 rpm and 1:20, respectively.

The maximum speed of the hydraulic pump is obtained

,max1

90 20 1800crankpn

nR

= = = rpm (16)

Table 3. Technical specifications of the selected components for SBIC

Component Specifications Values and Units

Bi-directional pump model PM10-A-11-S1-P12-00-10-R-20-05-A-00-00

Displacement (Variable type) 11.83 cc/rev

Theoretical flow (3600 rpm) 42.58 lpm

Theoretical absorbed power 23.07 kW

Theoretical absorbed torque 18.84 Nm

Moment of inertia 0.0014 kgm2

Swash plate angle control method Electro-proportional servo control 12 VDC

Weight of pump integrated servo control block 16.3 kg

Covering size 140 x 190 x 190 mm

Bi-directional motor model KM 1/5.5 G30A XXA 4NM2/0

Displacement (Fixed type) 5.45 cc/rev

Theoretical flow at speed 4000 rpm 22 lpm

Theoretical absorbed power 11 kW

Theoretical absorbed torque 105.1 Nm

Moment of inertia 35.7 x 10-6 kgm2

Maximum operating speed 4000 rpm

Weight of motor 2.6 kg


Proportional valve model spool valve type 4WRBA6XA30-2X/G24N9Z4/M-892

Nominal flow rate 28 lpm

Maximum working pressure 325 bar

Control signal Voltage range [0~10] VDC

Response time for 100% signal change Less than 70 ms

Weight 2.0 kg



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Therefore, the maximum displacement of the pump is required as

,max

,max,max

1000 17.32 10009.622

1800

tp

pp

QD

n

= = = cc/rev (17)

Finally, the hydraulic pump, hydraulic motor, and proportional control valve are

selected as given in Table 3.

Figure 5. A sketch drawing of the proposed SBIC

Figure 6. 3D views of the proposed SBIC

3. Verification of the designed SBIC

3.1. Installation Possibility of the designed HST on the bicycle frame

Based on the design concept 01 for a HST bicycle, the sketch drawing of the SBIC is

then carried out as displayed in Fig. 5. From Fig. 5, the considered problem is that how to

connect from the hydraulic pump control system to the pedal-crank and from the hydraulic

motor to the rear wheel shaft. The solution is using gear boxes in which the gears are

conical shapes. Therefore, based on all dimensions of the HST devices, the 3D graphs of the

proposed SBIC are built in Pro/Engineer design software and are shown in Fig. 6.

From Figs. 5 and 6, it can be seen that installation of the HST circuit on the bicycle

frame is possible. In the next section, stress and deformation analysis are performed in order

to verify the applicability of the SBIC for the life.

3.2. Stress and deformation analysis for the designed SBIC

3.2.1. Overview

Frame is one of the most important parts of a bicycle because it decides the stiffness as

well as balance condition of the product. Therefore, designing a suitable frame always

requires a lot of time and effort of engineers. A promising solution is to turn to a proven

tool of structural engineering: finite element analysis (FEA) method (8). The method plays a

major role in the design of almost all new airplanes, ships, bridges, and tall buildings built

today. The bike industry also realizes the potential value of FEA for improving product

designs and a faster development cycle(9)

.


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3.2.2. Model analysis method

The FEA process requires three types of input data: geometry, material properties, and

load distribution. For the bicycle frame, geometry means the overall frame dimensions

(such as tube lengths, intersection points, and angles) as well as the tubing specifications

(diameters, wall thickness, tapers, ovals, etc)(10)

. In the proposed SBIC structure, the

diamond frame as in classic bicycle designs is recommended on which the proposed HSTsystem is installed. Figure 7 displays the frame and geometrical dimension of SBIC.

(a) Proposed frame for the designed SBIC (b) Geometrical dimension of SBIC frame

Figure 7. SBIC frame structure

In order to balance between robust structure and economy effectiveness, alloy steel is

chosen to construct the bicycle frame. Properties of this steel can be consulted in Table 4.

Table 4.Material properties of alloy steel

Specifications Value & Units

Elastic modulus 2.1 x 1011N/m2

Poisson ratio 0.28

Mass density 7700 kg/m3

Yield strength 2.206x108N/m2

Ultimate tensile stress 6x108N/m2

a) SBIC loading analysis

The 75 kg rider is applied as the maximum load. It can be divided into 2 sub-weights,

called rider weight 1 and rider weight 2, which impact to the bicycle frame at two positions:

the rider seat and the pedal-crank shaft, respectively. For the stress and deformation

analysis, two cases are then carried out as riding mode and non-riding mode. In riding

mode, it is considered the total rider weight is concentrated the pedal-crank shaft as

depicted in Fig. 8a. Conversely, in non-riding mode, the rider load is distributed as 60 kg on

the seat and 15 kg on the pedal-crank shaft as in Fig. 8b. Because the HST is mostly

constructed by the hydraulic pump control system and the hydraulic motor, only these two

components are considered for loading force distribution. The weight of other components

in the HST are assumed 5 kg and distributed uniformly along the bicycle frame.

(a) Rider load in riding mode (b) Rider load in non-riding mode

Figure 8. Loading force distribution on the SBIC frame


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b) Stress and deformation analysis results

Parameters of FEA process are chosen as follows: mesh size 10mm, maximum mesh

angle 45o, force all feature includes 48375 nodes, refine based on element quality 23754

elements. Analyzing processes are carried out on a personal computer (Pentium Dual Core

2.8 Ghz, Random access memory 3 GB) with the support of Inventor 2010 design-modeling

software. The frame deformation and internal stress analyses are performed and the resultsare then in turn shown in Figs. 9 and 10. From these figures, it can be seen that the

maximum deformation and the maximum stress on the bicycle frame were 0.136 mm and

13.01x106 N/m

2, respectively. These values were small enough in comparison with the

characteristics (elastic modulus and yield strength) of the frame materials shown in Table 4.

As a result, it is realized that the proposed frame structure can make sure for users safety.

(a) Deformation analysis of the SBIC frame (b) Stress analysis of the SBIC frame

Figure 9. Analysis results in riding mode

(a) Deformation analysis of the SBIC frame (b) Stress analysis of the SBIC frame

Figure 10. Analysis results in non- riding mode

4. SBIC model designs and simulations

Here, three SBIC models based on the three design concepts have been built:

To investigate the operation of the HST circuit;

To build a control system for the main control unit to ensure the automatic control mode

of the SBIC with the desired criteria;

To investigate the energy regenerating ability of the SBIC with the concepts 2 and 3.

The SBIC models are built in the co-simulation environment which is a combination of

AMESim software and MATLAB/Simulink sofware. The HST circuit is built in AMESim

while the control system is built in the Simulink and then embedded into the AMESim.

4.1. SBIC Model 01 SBICM014.1.1. AMESim model

From Fig. 3 and the description, the model for the SBIC01 design named SBICM01 is

built as shown in Fig. 11.

Figure 11. SBICM01 model built in AMESim integrated Simulink controller


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directly controlled by a control signal, up, (within the range [0, 1]) defined as

,max,max

0 0

0

w

wpw w

w

IF T

TuIF T T

T

= <

(23)

( ),max

,max ,max

0

1 0

p w

p

p p w w

D IF TD

u D IF T T

= <

(24)

where: ,max 90NmwT = is determined from the normal maximum torque of the rear wheel.

b) Braking control

The purpose of this control task is to keep the rider and bicycle in safety in all cycling

conditions. In traditional bicycle designs, the rider applies a braking force by using one or

both of the mechanical brakes including: front brake and rear break drum brake. However,

the use of front brake can cause dangerous for the rider as well as the bicycle, especially in

case of going downhill. Therefore, in the proposed SBIC01, the front brake is replaced by

the hydraulic brake with the two control modes. Besides the manual braking mode, the

automatically braking mode helps the rider to fast react to the emergency cases, for

example, so fast going downhill. As the result, the rider and bike become safer.

The braking action is decided by the braking command, ubr, outputted from the

controller which is decided based on the differential of the wheel torque.

( )

( ) ( )

0 0

; 0 , 0 10 & 0

w

br br w wbr w

IF T

u udT dT k IF T

dt dt

= < <

(25)

where: ,andbrk are a suitable constants to adjust the valve control signal range.

( )1 brValveOpenArea u MaxOpenArea= (26)

4.1.3. Simulation results

The simulated load profile is generated during 120 seconds as shown in Fig. 12(a). The

control target is to select continuously the suitable transmission ratio to ensure the output

power is a constant corresponding to the constant speed of the pedaling.

(a) Simulated loading torque (b) Flow rate at hydraulic pump port

(c) Pressure at hydraulic pump port (d) Output energy at the rear wheel shaft

Figure 12. Simulation results with the SBICM01


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The simulation result shown in Fig. 12(d) depicts the output energy curve with respect

to cycling time while the pump control performance is expressed by Figs. 12(b) and (c).

From this figure, it can be seen that the output power reaches to a linear trajectory. That

means the output power is mostly kept as a constant. On the other words, the SBICM01

control system has enough ability to create a cyclist comfortable for the rider.

In addition, the system working efficiency is also a very important factor to evaluate thebicycle design. From the simulation results, the efficiency of the SBICM01 is obtained as

01

01

01

4.44943100 100 97.84%

4.54754

HSBICM Output

HSBICM

HSBICM Input

EEff

E= =

(27)

The result in Eq. (27) proves the effectiveness of using the proposed SBICM01 to

achieve the high working efficiency.

4.2. SBIC Model 02 SBICM02

4.2.1. AMESim model

A model named SBICM02 is built for the designed bicycle concept 02 (SBIC02). In this

model, the HST circuit is integrated with the energy regenerative circuit (see Fig. 3). For

evaluating the energy regenerative capacity of the SBICM02, the block Regenerated

Power has been built in the AMESim model. This measured energy is based on Eq. (28)

( )020

, kJ30000

endt

HSBICM Gen gen genE T n dt

= (28)

where: Tgenand ngenare the torque and speed of the electric generator.

The setting parameters for the SBICM02 are taken from 2.

4.2.2. Simulink controller

As described, the proposed SBIC02 bicycle has the main advantages which are two

control modes, and the ability in regenerating energy during braking phase when the bicycle

goes downhill or decelerates.

a) Automatic control mode

The controller is designed with the two functions, pump displacement control and

braking control, as the same as the control system in the SBICM01 (4.2.1).

b) Energy regenerative control

In this SBICM02model, only the energy regenerative capacity during the braking

actions of the drum brake is considered while the way to use this energy such as for

acceleration, going uphill is not concerned. The clutches are then used to perform the

ON/OFF logic to recovery the energy when the rider applies braking forces to the drum

brake. During braking actions on the drum brake, the clutches 1 and 2 are disconnected

(control signal = 1) while the clutch 3 is connected (control signal = 0) to convert most of

kinetic energy into rotational torque and speed of the electric generator. On the contrary,

during other operations, the clutches 1 and 2 are connected while the clutch 3 is

disconnected to create the automatic transmission for the bicycle.


The simulations have been carried out to evaluate the performance of the designed

SBICM02. The simulated load profile is also generated during 120 seconds as shown in Fig.

13(a). As a result, the system working performance is then expressed by Figs. 13(b)~(d).

Based on the road profile, the rider applies braking forces to the drum brake. The clutches

01 and 02 are then directly controlled by the braking control signal while the clutch 03 is

controlled by the inversed control signal as

03 031 ; 0 1 1 0c br br cu u u or u or = = = (29)

Consequently, the working performance of the hydraulic pump is then displayed in

Figs. 13(b) and (c). The results show that the pump displacement is well controlled with

respected to the variation of the load profile.

The system working efficiency of the SBICM02 is obtained as


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(c) Pressure at hydraulic pump port (d) Energy comparison


02

02

02

37.1108100 100 96.32%

38.5271

HSBICM Output

HSBICM

HSBICM Input

EEff

E= =

(30)


achieve the high working efficiency. Furthermore, by using the electric generator to

regenerate the energy during the braking states, the energy has been recovered and can be

stored by the battery. The amount of generated energy during the test process is 8.23 kJ

which is about 21.36 % compared to the input energy (Fig. 13(d)). It strongly points out that

the SBIC model 02 brings not only a high performance but also a good economics.

4.3. SBIC Model 03 SBICM03

A model named SBICM03 is built for the designed bicycle concept 03 (SBIC03),

consequently, the AMESim model is as same as that of the SBICM02 (see 4.2). The

difference between the SBICM03 and SBICM02 is the automatic control system. In this

model, the bicycle is design in order to achieve three following targets:

Automatic/Manual transmission control mode with multi-speed selection;

Adaptive Human Power (AHP) controller is integrated into the automatic control mode;

Energy regenerative ability.4.3.1. AMESim model

It can be seen that the SBICM03 only differs from the SBICM02 about the Automatic

Control Mode. Here, there are control two inputs, the pedaling speed and the torque at rear

wheel shaft, and two control outputs which are the control signals for the hydraulic pump

and proportional control valve.

4.3.2. Simulink controller

As the description for the SBIC03 concept, this bicycle has two main advantages:

There are two control modes: automatic control mode and manual control mode.

Moreover, the adaptive human power control technique is also integrated in the

automatic control mode to create for the controller a human power feeling which helps

to classify the power of the rider such as: strong, medium, weak, etc. With this ability,

the controller can adjust the pump displacement not only corresponding to the output


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249

torque but also corresponding to the human power input. Consequently, this bicycle

design can bring to the user a very cyclist comfortable.

The ability in regenerating energy during braking phase when the bicycle goes downhill

or decelerates.

a) Automatic control mode

The controller is designed with the two functions: pump displacement control andbraking control. The braking control task is built as the same as the control system in the

SBIC model 01 and model 02 (see 4.2.1). Meanwhile, the detail design of the pump

displacement control task is given as the following description.

The purpose of this control task is to adjust the transmission ratio between the pedaling

speed and the rear wheel speed with respect to the two factors (the pedaling speed and the

loading torque measured on the rear wheel shaft) by tuning the swash plate angle. In other

words, the HST functions as a transmission system with infinite ratio or a multi-speed

transmission system. The description in 3.1.2a shows clearly why changing the pump

swash plate angle with respect to the loading torque variation can bring to the rider a cyclist

comfortable. However, there is also one remained factor which can improve the cyclist

quality. It is the power of the rider. The human power feeling concept is based on physicalactions of the rider corresponding to a road which causes the loading torque increasing.

With the riders are people who possess small power (such as children, elders), the pedaling

speed will be reduced when going to a road profile requesting high supply torque. On the

other hand, with the riders are people who possess large power (such as adults), the

pedaling speed might not be reduced when going to the same road.

From Eqs. (21), (22), and the above human power feeling concept, the controller is

designed to ensure a fixed output power corresponding as:

Case 01: for an increase in rear wheel torque: the wheel speed needs to be reduced,

consequently, the pump displacement needs to be reduced.

Case 02: for a decrease in rear wheel torque: the wheel speed needs to be increased,

consequently, the pump displacement needs to be increased. The amount of swash angle reduction or increment is depended on the rider power:

+ For case 01: the larger human power is, the smaller reduction of the swash angle is

needed; and vice versa;

+ For case 02: the larger human power is, the larger increment of swash angle is needed;

and vice versa.

Based on the above principle, the pump displacement is directly controlled by a control

signal, up, (within the range [0, 1]) defined by rules shown in Eqs. (31) and (32)

,max,max

0 0

0

w

wpw w

w

IF T

TuIF T T

T

= <

(31)

( ),max

,max ,max

0

1 0

p w

p

hp p p w w

D IF TD

k u D IF T T

=

<

(32)

where: ,max 90NmwT = is determined from the normal maximum torque of the rear wheel,khpis a so-called sensitive gain which is defined based on the rider power.

First of all, a variable called sensing power factor is defined as

[ ] [ ],max

,max

, 0,1 , 1,1

r

r rhp hp

r

nd

n n

dt n

= (33)

The control logic for this gain is then derived as following 4 rules:

Rule 01: ( ) ( )0 & 0 1w hpIF T THEN [ ]0.3 0.3 , 0,0.3hp hp hpk k= (34)


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250

Rule 02: ( ) ( )0 & 0.2 0w hpIF T THEN < ( ]0.3 3 , 0.3,0.9hp hp hpk k= (35)

Rule 03: ( ) ( )0 & 1 0.2w hpIF T THEN < ( ]0.7 , 0.9,1.7hp hp hpk k= (36)

Rule 04: ( )0 : 0w hpIF T THEN k< = (37)

From Eqs. (31)~(37), the automatic control mode can enhance a good performance.

b) Energy regenerative control

The SBICM03, has the same energy regenerative control mode as that of the SBICM02.

Therefore, the energy regenerative control is followed the design in the SBICM02.


(c) Pressure at hydraulic pump port (d) Energy comparison



The simulations have been carried out to evaluate the working performance of the

designed SBIC model 03. The testing conditions are the same as those when testing the

SBICM02. It is seen that the pedaling speed is constant with 75 rpm. That means the rider is

strong and has enough ability to go uphill without reducing the cycling speed. As a result,

the system working performance is then expressed by Figs. 14(b)~(d).

Based on the road profile, the rider applies braking forces to the drum brake. The

clutches 01 and 02 are directly controlled by the braking control signal while the clutch 03is controlled by the inversed control signal as shown in Eq. (32). Consequently, the working

performance of the hydraulic pump is then displayed in Figs. 14(c) and (d). The results

show that the pump displacement is well controlled with respected to the variation of the

load profile (Fig. 14(a)) and the braking control signal.

The system working efficiency of the SBICM03 is obtained as

02

02

02

52.266100 100 96.64 %

54.081

HSBICM Output

HSBICM

HSBICM Input

EEff

E= =

(38)


achieve the high working efficiency. Furthermore, by using the electric generator to

regenerate the energy during the braking states, the energy has been recovered and can be

stored by the battery. The amount of generated energy during the test process is 15.744 kJ

which is about 29.11 % compared to the input energy. It strongly points out that the SBIC


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model 03 obtains the highest working efficiency (Fig. 14(d)).

5. Conclusions

This paper develop the newly concept for a hydraulic bicycle with automatic

transmission and energy recuperating ability which is named smart bicycle (SBIC). The

SBIC operation is based on a hydrostatic transmission (HST). Three HST designs for thebicycle have been proposed. The key components in these HST are a hydraulic pump, a

hydraulic motor, a small reservoir, hoses, valves and a main control unit to store and

manage power of the pedal-crank. Moreover, a use of energy converting and storing

devices, such as an electric generator and a battery, respectively, is an optional design for

the bicycle. This design is to recovery the energy during the deceleration or going downhill

process and then to support this energy amount to the hydraulic system during the

acceleration or going uphill process. As the result, the bicycle efficiency is increased.

The designed SBIC is then validated to ensure the design possibility as well as its stress

and deformation. In addition, the three models with respect to the three SBIC designs have

been built in the co-simulation of AMESim and MATLAB/Simulink. The simulations have

been then carried out to carefully investigate the working performances of the proposedbicycle designs. The simulation results prove clearly that the third design SBIC03 could

bring the best solution for bicycle design technology. The overall transmission efficiency in

this design could theoretically become competitive with the roller-chain technology.

References

(1) Socks, M.T., 2006. Design of a High-Efficiency Hydrostatic Bicycle Transmission. Thesis

(S.B.).

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(3) Schmidt, T., Wilson, D.G., 2003-2004. Human Power. Technical Journal of the

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(5) Rahmfeld, R., 2000. Development and Control of Energy Saving Hydraulic Servo

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