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Design and implementation of an air-powered motorcycles
Applied Energy 86 (2009) 1105–1110
Contents lists available at ScienceDirect
Applied Energy journal homepage: www.elsevier.com/locate/apenergy
Design and implementation of an air-powered motorcycles Yu-Ta Shen a,*, Yean-Ren Hwang b a b
Department of Mechanical Engineering, National Central University, Wu-Chung Li 38, Chong-Li, Taiwan, ROC Department of Mechanical Engineering, National Central University, Wu-Chung Li 38, Chong-Li, Taiwan 320, ROC
a r t i c l e
i n f o
Article history: Received 3 September 2007 Received in revised form 17 June 2008 Accepted 18 June 2008 Available online 31 July 2008 Keywords: Clean energy Air motors Motorcycle Speed control
a b s t r a c t Currently in Taiwan, there are more than 13 million motorcycles, mostly driven by internal combustion engines, and the pollutants, carbon monoxide (CO) and unburnt hydrocarbons (HC), generated by motorcycle are responsible for more than 10% of the air pollutants released to the atmosphere. The studies show that the internal combustion engines of motorcycles may generate up to two times more pollutants than those of automobiles. In order to improve the air pollution condition and eliminate the pollutants exhausting, this paper presents a new idea of using compressed air as the power sources for motorcycles. Instead of an internal combustion engine, this motorcycle is equipped with an air motor, which transforms the energy of the compressed air into mechanical motion energy. A prototype is built with a fuzzy logic speed controller and tested on the real road. The experiment data shows that the speed error is within 1 km/h and the efficiency is above 70% for this system when the speed is over 20 km/h. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The air pollution, recently believed as the reason for causing the global warming and dramatic climate change of the earth, has been a severe problem for many years. One major source of the air pollutants is generated by burning fossil fuel through the internal combustion engines for transportation vehicles. There are basically three forms of pollutants produced from vehicles: unburnt hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). As a notorious example, the motorcycles are the most popular transportation vehicle in Taiwan with total amount more than 13 million. The pollutants, unburnt hydrocarbons (HC) and carbon monoxide (CO), produced by motorcycles are responsible for more than 10% of the air pollutants in Taiwan [1]. Currently in Taiwan, riding motorcycle or scooter is convenient and it may be preconceived by the general public that motorcycles must be cleaner burning than cars since they are so much smaller and lighter, but this is not exactly the truth. According to the studies of Taiwan EPA [1], the 50 cc scooter (two-stroke engine) emits 2.7 times as mass of carbon monoxide (CO) and 6.7 times as much unburnt hydrocarbons as automobile produced in grams per kilometer. For 125 cc scooter (four-stroke engine), it is 2.4 times and 3.1 times as much as automobile produced, respectively. Nowadays, there are many new types of motorcycle, including the fuel cell driven [2–4] and the hybrid energy driven motorcycles. The hybrid energy includes internal combustion engine and * Corresponding author. E-mail addresses: [email protected] (Y.-T. Shen), [email protected] (Y.-R. Hwang). 0306-2619/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2008.06.008
electric motor or pneumatic motor. Sheu et al. [5–6] and Tzeng [7] proposed a parallel hybrid motorcycle transmission system to improve the transmission power performance. Tzeng et al. also presented other hybrid pneumatic power in motorcycle [8–9] to investigate and develop the pneumatic motor combined with internal combustion engine. The previous studies focus on using the new transmission system to lower the pollutant emission. These methods may be the one of the most capable substitute transportation, but these systems are still releasing a smaller amount of pollutants into the air. For the conception of green energy, in this paper, we propose a new design of motorcycle which uses the compressed air as its power source so that it will be truly free of pollution for the environment. The air motors convert the energy of compressed air into the mechanical transportation energy. In general, they are safer, cleaner, cheaper and with higher power-to-weight ratio compared to electrical motors [10]. During past decades, their industrial applications have been increased for special working conditions, such as in spark-prohibited environments, mining plants, and chemical manufactories. For most cases, the air motors has been employed on the equipments with lower precision requirement [11]. However, the demand for high precision air motors has been increasing during past few years, and hence many researches have been conducted for their dynamic characteristics [12–14] and their applications to replace traditional electrical motors [15]. There are many types of hybrid engine to apply for the transportation vehicle. The purpose of these engines is trying to reduce air pollution, but these engines are still implementing the internal combustion engine which driven motorcycles have been shown generating more pollutants than those of automobiles. In order
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Nomenclature D E Ga Gt kP kI ~p k ~ k i
kxi n Dp Q R Rg ~SEi
the variation rate of error E the error of the system output to desired output the teeth of gear connected to the air motor the teeth of gear assembled on the motorcycle’s rear tire the parameter of the proportion the parameter of the integral the corresponding fuzzy variable of kP the corresponding fuzzy variable of kI the maximum value of ith fuzzy membership functions of ~Skx the revolution per second of air motor the different pressure from inlet to outlet of air motor the airflow value under compressed condition the radius of motorcycle tire the gear ratio of the air motor to the motorcycle’s rear tire the corresponding fuzzy sets of E
to improve the air pollution condition and eliminate the pollutants exhausting to the atmosphere, a prototype motorcycle using a compressed air as its power source is presented in this paper. A fuzzy logic speed controller is also developed to maintain the constant speed motion. The efficiency of the overall system will be analyzed through the experiment data. The following sections are organized as follows: the introduction to air motor is described in Section 2, the fuzzy control algorithm was presented in Section 3, the experiment results are shown and analyzed in Section 4 and the conclusion is stated in Section 5. 2. The principles of an air motor Fig. 1 shows the sketch map of a vane-type air motor. There is a rotational drive shaft with four slots, each of which is fitted with a freely sliding rectangular vane. When the drive shaft starts to rotate, the vanes tend to slide outward due to centrifugal force and are limited by the shape of the rotor housing. Depending on the flow direction, this motor will rotate in either clockwise or counterclockwise directions. The difference of air pressure at the inlet and outlet will provide the torque required to move the shaft. Hence, the higher flow rate and the larger pressure difference will provide larger toque on the shaft and higher rotational speed. The air-powered motorcycle system, with its schematic diagram shown in Fig. 2, consists of an air motor (GAST 6AM, max out-
~SDi ~S kp ~S
the corresponding fuzzy sets of D the corresponding fuzzy sets of kP the corresponding fuzzy sets of kI ki T the torque of the air motor U the control input signal calculated from digital signal processor lEi~ ðxÞ the degree of membership that E belongs to ~SEi lDi the degree of membership that D belongs to ~SDi ~ ðxÞ ~ lEi\ ~ Di ~ ðxÞ the degree of membership that ‘‘E belongs to SEi ” and ‘‘D belongs to ~SDi V the control voltage to the electronic proportional directional control valve the motorcycle speed Vm w the angular velocity of the air motor the air motor rotational speed wa the weighted value of the membership function wi g the efficiency of the air motor
put power is 4 horsepower (hp) and max torque is 13 (N m), an air tank, an electronic proportional directional control valve (FESTO MPVE), a filter/regulator with lubricant (SHAKO FRL-600), a pressure sensor (KEYENCE AP-C33W), an airflow meter (DWYER) and a digital signal processor (DSP TI C240). The airflow path starts from the air tank through the filter, control valve and finally enters the air motor. The airflow entry into motor will be determined by the valve position, which is controlled by externally applied voltage, denoted by v. When v equals 5 voltage (V), the valve will stay at the middle and both left and right entries will be closed. The valve will move to a right position when v is above 5 V and fully open when v is equal to 10 V. Similarly, the valve will move left if v is less than 5 V and will be fully opened at 0 V. The direction of the air motor depends on whether the voltage v is above or below 5 V. The control input from DSP, denoted by u, will be converted into v as v = u + 5. The major elements of air dynamic system and their functions are listed in Table 1. The experiment results between v and the rotational speed of the air motor is shown in Fig. 3. The signal of u was either linearly increased or linearly decreased by DSP following the cycle 0 V ? 2.5 V ? 2.5 V ? 0 V with a two-second period. The deadzone and hysteretic phenomena were found as shown in Fig. 3. During the increasing procedure, the motor remained motionless when u was set less than 1 V. After exceeding 1 V, the voltage and rotational speed demonstrated near linear relationship. When the voltage was reduced from 2.5 V to 0 V, the speed–voltage relationship did not follow the same curve of rising up but demonstrated a nonlinear behavior. The air motor stopped around 0.8 V instead of 1 V. Similar results were found for u below 0 V. These phenomena were due to the friction in the mechanism and the pressure drop of the supply air at the starting moment. The air pressure was found dropping about 0.8 (kgf/cm2) at the moment of valve opening and returning to its normal values after a short period of time. For instance, if the air pressure was set to 1 (kgf/ cm2), the actual air pressure at the moment of valve opening will drop to 0.2 (kgf/cm2), which was not enough to overcome the static friction and hence caused the delay the system’s response. The efficiency of an air motor is defined as the ratio of the output shaft energy to the input energy of air motor as follows [8]
g¼
Fig. 1. Vane-type air motor.
wT 2pnT ¼ DpQ DpQ
ð1Þ
where w (rad/s) represents the angular velocity of the air motor, Dp (kgf/cm2) represents the different pressure from inlet to outlet of air
Y.-T. Shen, Y.-R. Hwang / Applied Energy 86 (2009) 1105–1110
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Fig. 2. The ideal schematic diagram of air dynamic motorcycle.
Table 1 The equipment of air-powered motorcycle Elements
Function
1 Air tank 2 Filter/lubricant
Store up and provide air Filter the water in the air and avoid the inner of air motor to become rusty. The lubricant will lubricate the air motor Modulate the amount of entering air and control the speed of air motor Calculate the amount of airflow Provide the power Calculate the pressure of airflow Output the analog signal to the electronic control valve
3 Electronic control valve 4 Airflow meter 5 Air motor 6 Pressure sensor 7 Digital controller
g¼
2pnT 2p 2:45 5 ffi 0:4 ¼ 40%: ¼ ðDpÞQ 0:34 583:33
The rear gear assembled on the motorcycle’s rear tire is three time of that of the gear connected to the air motor. This means that the velocity and acceleration of the motorcycle can be obtained by converting the air motor rotational speed and angular acceleration, respectively. For instance, the radius of motorcycle tire is R, the teeth of gear connected to the air motor is Ga, the teeth of gear assembled on the motorcycle’s rear tire is Gt, the air motor rotational speed is wa from the encoder, the motorcycle speed can be calculated as V m ¼ 2pR wa Rg , where Rg ¼ Ga =Gm is the gear ratio between two axes. The data of the air pressure, air flow and the rotational speed of the air motor can be directly measured during the experiment. Therefore, the efficiency of the overall system can be calculated through Eq. (1). 3. Fuzzy control design The experiment results shown that the dead-zone and hysteretic behavior should not be neglected if one wishes to achieve good performance. In order to improve the performance, we implemented a fuzzy logic with PI (proportional integral) control scheme for the air motorcycle system. Two major consecutive steps were designed in this controller. First, we tried to choose best parameters for proportional integral controller only based on the error and its integration as described in Eq. (2)
uðtÞ ¼ kP eðtÞ þ kI
Fig. 3. The relationship between the voltage v and the rotational speed.
motor, T (kgf cm) represents the torque of the air motor, Q (cm3/s) represents the airflow value under compressed condition and n (rps) represents the revolution per second. For instance, if the velocity is controlled at 5 km/h and the different from inlet to outlet pressure of air motor is Dp = 0.34 (kgf/cm2), and the airflow value is kept as Q = 35 (L/min) = 583.33 (cm3/s), n = 2.45 (rps), T = 5 (kgf cm). The efficiency can be calculated as follows:
Z
eðsÞ ds
ð2Þ
As a result of the nonlinear properties of dead-zone and hysteretic behaviors, the selections of kP and kI should be different for different reference speeds and also for different stages of the dynamic responses. Hence, we implemented the fuzzy logic control to improve the system performance. Because the friction and hysteretic behaviors played a significant role when system was at low speed range, the additional control inputs must be considered to compensate these effects. However, these compensations may deteriorate the system performance by introducing large overshoot and chattering. Hence, the compensation should be attenuated once the nonlinear effects become less dominant. At the beginning stage, large kP and kI were required to obtain enough control power to overcome static
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friction and improve the transient response. After the transient period, kP and kI decrease to small values to maintain good performance at the steady state stage. However, sudden switch of kP and kI will deteriorate the performance and result in larger setting time. Hence, we developed the switching rules based on the following fuzzy inference rules
IF E belongs to S~Ei AND D belongs to ~SDi ; ~ belongs to ~S ~p belongs ~S AND k THEN k i kp ki
ð3Þ
where E and D represent error and its variation rate, respectively, ~SEi ~p and k ~ represent and ~ SDi represent the corresponding fuzzy sets, k i the corresponding fuzzy variable of kP and kI, and their corresponding fuzzy sets are represented as ~Skp and ~Ski , respectively. Although one could choose any types of membership functions, the triangle shape functions were used in this paper because of their simpliciSki are shown in ties. The membership functions of ~SEi , ~SDi ; ~Skp and ~ Figs. 4 and 5. The notations in these figures, NL, NM, NS, PS, PM, PL, ZE, etc., represent the fuzzy sets. For instance, NL represents ‘‘negative large”, PS represents ‘‘positive small”, and so on. The ‘AND’ operation of two fuzzy sets ~ SEi and ~ SDi was first proposed by Zadeh [16] as follows:
lEi\ ~ Di ~ ðxÞ ¼ minflEi ~ ðxÞ; lDi ~ ðxÞg
Fig. 7. The road test.
ð4Þ
Fig. 4. The fuzzy membership functions ~ SEi for the error E.
Fig. 5. The fuzzy membership functions ~ SDi for the error rate D.
Fig. 6. The chain connects air motor with rear wheel.
Fig. 8. (a) The velocity of air-powered motorcycle. (b) The velocity of air-powered motorcycle.
Y.-T. Shen, Y.-R. Hwang / Applied Energy 86 (2009) 1105–1110
where lEi ~ ðxÞ and lDi ~ ðxÞ are the degree of membership that E and D SDi , respectively, and lEi\ belongs to ~SEi and ~ ~ Di ~ ðxÞ is the degree of SDi . Another membership that ‘‘E belongs to ~SEi ” and ‘‘D belongs to ~ widely used definition for the ‘AND’ operation on fuzzy sets is the algebraic product, that is
lEi\ ~ Di ~ ðxÞ ¼ lEi ~ ðxÞ lDi ~ ðxÞ:
ð5Þ
In this paper, we adopted the latter definition because of its simplicity and easy for implementation.Defuzzification is the process of converting a fuzzy quantity which was represented by a membership function to a crisp value. The weighted average method is commonly used in industry. It defines the crisp value as the weighted average of membership functions. This method is valid only for the case when the output membership function is a union result of several fuzzy quantities [17]
kx ¼
n X i¼1
, wi kxi
n X
wi
ð6Þ
i¼1
where the index x represents either p or i, and kxi represented the maximum value of ith fuzzy membership functions of ~Skx and wi represented the weighted value of that membership function. Fig. 10a shows the velocity compare to the pressure difference between inlet and outlet. It is shown that if the velocity increases, the pressure difference also increases. The riding speed of the motorcycle is controlled by the driver with a throttle through the controller, which adjusts the electromagnetic valve based on the pressure difference between the inlet and outlet. The fuzzy PI con-
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trol rules are used to determine the control voltage signal to electromagnetic control valve according to the velocity. 4. Assembly and experiment for the air-powered motorcycle A SYM 125 cc motorcycle was modified for this experiment. The four-stroke engine, gasoline tank, carburetor, battery and exhausting pipe of the motorcycle were deprived from the body. At the same time, an air motor, a 10 l air tank (100 kgf/cm2), an air filter and an electromagnetic control valve were installed on the motorcycle. Fig. 6 shows the actual assembly of the transmission system of the air-powered motorcycle. The overall weight, including motorcycle, air tank and driver, is about 150 kg. The practical riding test on the road was shown in Fig. 7. By applying the control algorithm presented in last section, the time histories of the motorcycle speed are shown in Fig. 8a. The speeds were set as from 5 km/h to 30 km/h. It is found that the rising time of all settings are almost the same while the larger acceleration were generated for higher speed setup. Due to the compressibility of the air and the friction of the mechanism, the time delay becomes more obvious for lower speed setup. The final speed errors for all cases are less than 1 km/h. In Fig. 8b, the driver adjusted the throttle from a constant velocity to a higher. The controller can modify the best riding velocity and stabilize it according to the different pressure which was caused by the throttle. As shown in Fig. 9, the efficiency of this system, approximated by a polynomial curve y, increases for larger speed setup and approaches to its maximum around 75%. The efficiency is over 70%
Fig. 9. The efficiency of air dynamic motorcycle, y is a function of polynomial asymptotic curve.
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Fig. 10. (a) The different pressure from inlet to outlet of air dynamic motorcycle. (b) The air flow of air dynamic motorcycle. y is a function of polynomial asymptotic curve.
when the motorcycle’s speed is higher than 20 km/h and does not increase too much for higher speed. The corresponding pressure difference Dp and the airflow Q were shown in Fig. 10. The asymptotic curves of y were almost linear for both cases. These mean that Dp and Q are basically proportional to the speed. The larger speed is, the larger pressure difference and more air flow will be required for the motorcycle. The power source of the motorcycle is a 10 l/100 kgf/cm2 commercial tank, which is refilled by a 7 kW compressor with 75 s. According to the experimental results, with this tank, the motorcycle will run for 2 km for the overall weight of motorcycle as 150 kg. Therefore, the power-consuming for this motorcycle will be about 0.073 kw-hr per kilometer. For a commonly used internal combusting engine motorcycle in Taiwan SYM 125 (10 Hp, 60 km/ h) the consuming power is about 0.127 kw-hr per kilometer. Although the efficiency is higher for the prototype air-powered motorcycle, the transportation distance is not practically enough at the current stage. However, the distance can be increased by equipping a larger volume or higher pressure tank. 5. Conclusion An air-powered motorcycle with fuzzy logic controller has been proposed and tested. The experiment data shows that the speed error of the motorcycle is within 1 km/h and the efficiency is above 70% for this system when its speed is over 20 km/h. The powerconsuming for this prototype is about 0.073 kw-hr per kilometer compared to 0.127 kw-hr per kilometer for a commonly used internal combusting engine motorcycle. Although the efficiency is higher for the prototype, the transportation distance is not enough at the current stage. The future research will be focused on improving
the efficiency and extending the transportation distances for the air-powered motorcycle. References [1] Taiwan EPA,
Contents lists available at ScienceDirect
Applied Energy journal homepage: www.elsevier.com/locate/apenergy
Design and implementation of an air-powered motorcycles Yu-Ta Shen a,*, Yean-Ren Hwang b a b
Department of Mechanical Engineering, National Central University, Wu-Chung Li 38, Chong-Li, Taiwan, ROC Department of Mechanical Engineering, National Central University, Wu-Chung Li 38, Chong-Li, Taiwan 320, ROC
a r t i c l e
i n f o
Article history: Received 3 September 2007 Received in revised form 17 June 2008 Accepted 18 June 2008 Available online 31 July 2008 Keywords: Clean energy Air motors Motorcycle Speed control
a b s t r a c t Currently in Taiwan, there are more than 13 million motorcycles, mostly driven by internal combustion engines, and the pollutants, carbon monoxide (CO) and unburnt hydrocarbons (HC), generated by motorcycle are responsible for more than 10% of the air pollutants released to the atmosphere. The studies show that the internal combustion engines of motorcycles may generate up to two times more pollutants than those of automobiles. In order to improve the air pollution condition and eliminate the pollutants exhausting, this paper presents a new idea of using compressed air as the power sources for motorcycles. Instead of an internal combustion engine, this motorcycle is equipped with an air motor, which transforms the energy of the compressed air into mechanical motion energy. A prototype is built with a fuzzy logic speed controller and tested on the real road. The experiment data shows that the speed error is within 1 km/h and the efficiency is above 70% for this system when the speed is over 20 km/h. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The air pollution, recently believed as the reason for causing the global warming and dramatic climate change of the earth, has been a severe problem for many years. One major source of the air pollutants is generated by burning fossil fuel through the internal combustion engines for transportation vehicles. There are basically three forms of pollutants produced from vehicles: unburnt hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). As a notorious example, the motorcycles are the most popular transportation vehicle in Taiwan with total amount more than 13 million. The pollutants, unburnt hydrocarbons (HC) and carbon monoxide (CO), produced by motorcycles are responsible for more than 10% of the air pollutants in Taiwan [1]. Currently in Taiwan, riding motorcycle or scooter is convenient and it may be preconceived by the general public that motorcycles must be cleaner burning than cars since they are so much smaller and lighter, but this is not exactly the truth. According to the studies of Taiwan EPA [1], the 50 cc scooter (two-stroke engine) emits 2.7 times as mass of carbon monoxide (CO) and 6.7 times as much unburnt hydrocarbons as automobile produced in grams per kilometer. For 125 cc scooter (four-stroke engine), it is 2.4 times and 3.1 times as much as automobile produced, respectively. Nowadays, there are many new types of motorcycle, including the fuel cell driven [2–4] and the hybrid energy driven motorcycles. The hybrid energy includes internal combustion engine and * Corresponding author. E-mail addresses: [email protected] (Y.-T. Shen), [email protected] (Y.-R. Hwang). 0306-2619/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2008.06.008
electric motor or pneumatic motor. Sheu et al. [5–6] and Tzeng [7] proposed a parallel hybrid motorcycle transmission system to improve the transmission power performance. Tzeng et al. also presented other hybrid pneumatic power in motorcycle [8–9] to investigate and develop the pneumatic motor combined with internal combustion engine. The previous studies focus on using the new transmission system to lower the pollutant emission. These methods may be the one of the most capable substitute transportation, but these systems are still releasing a smaller amount of pollutants into the air. For the conception of green energy, in this paper, we propose a new design of motorcycle which uses the compressed air as its power source so that it will be truly free of pollution for the environment. The air motors convert the energy of compressed air into the mechanical transportation energy. In general, they are safer, cleaner, cheaper and with higher power-to-weight ratio compared to electrical motors [10]. During past decades, their industrial applications have been increased for special working conditions, such as in spark-prohibited environments, mining plants, and chemical manufactories. For most cases, the air motors has been employed on the equipments with lower precision requirement [11]. However, the demand for high precision air motors has been increasing during past few years, and hence many researches have been conducted for their dynamic characteristics [12–14] and their applications to replace traditional electrical motors [15]. There are many types of hybrid engine to apply for the transportation vehicle. The purpose of these engines is trying to reduce air pollution, but these engines are still implementing the internal combustion engine which driven motorcycles have been shown generating more pollutants than those of automobiles. In order
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Nomenclature D E Ga Gt kP kI ~p k ~ k i
kxi n Dp Q R Rg ~SEi
the variation rate of error E the error of the system output to desired output the teeth of gear connected to the air motor the teeth of gear assembled on the motorcycle’s rear tire the parameter of the proportion the parameter of the integral the corresponding fuzzy variable of kP the corresponding fuzzy variable of kI the maximum value of ith fuzzy membership functions of ~Skx the revolution per second of air motor the different pressure from inlet to outlet of air motor the airflow value under compressed condition the radius of motorcycle tire the gear ratio of the air motor to the motorcycle’s rear tire the corresponding fuzzy sets of E
to improve the air pollution condition and eliminate the pollutants exhausting to the atmosphere, a prototype motorcycle using a compressed air as its power source is presented in this paper. A fuzzy logic speed controller is also developed to maintain the constant speed motion. The efficiency of the overall system will be analyzed through the experiment data. The following sections are organized as follows: the introduction to air motor is described in Section 2, the fuzzy control algorithm was presented in Section 3, the experiment results are shown and analyzed in Section 4 and the conclusion is stated in Section 5. 2. The principles of an air motor Fig. 1 shows the sketch map of a vane-type air motor. There is a rotational drive shaft with four slots, each of which is fitted with a freely sliding rectangular vane. When the drive shaft starts to rotate, the vanes tend to slide outward due to centrifugal force and are limited by the shape of the rotor housing. Depending on the flow direction, this motor will rotate in either clockwise or counterclockwise directions. The difference of air pressure at the inlet and outlet will provide the torque required to move the shaft. Hence, the higher flow rate and the larger pressure difference will provide larger toque on the shaft and higher rotational speed. The air-powered motorcycle system, with its schematic diagram shown in Fig. 2, consists of an air motor (GAST 6AM, max out-
~SDi ~S kp ~S
the corresponding fuzzy sets of D the corresponding fuzzy sets of kP the corresponding fuzzy sets of kI ki T the torque of the air motor U the control input signal calculated from digital signal processor lEi~ ðxÞ the degree of membership that E belongs to ~SEi lDi the degree of membership that D belongs to ~SDi ~ ðxÞ ~ lEi\ ~ Di ~ ðxÞ the degree of membership that ‘‘E belongs to SEi ” and ‘‘D belongs to ~SDi V the control voltage to the electronic proportional directional control valve the motorcycle speed Vm w the angular velocity of the air motor the air motor rotational speed wa the weighted value of the membership function wi g the efficiency of the air motor
put power is 4 horsepower (hp) and max torque is 13 (N m), an air tank, an electronic proportional directional control valve (FESTO MPVE), a filter/regulator with lubricant (SHAKO FRL-600), a pressure sensor (KEYENCE AP-C33W), an airflow meter (DWYER) and a digital signal processor (DSP TI C240). The airflow path starts from the air tank through the filter, control valve and finally enters the air motor. The airflow entry into motor will be determined by the valve position, which is controlled by externally applied voltage, denoted by v. When v equals 5 voltage (V), the valve will stay at the middle and both left and right entries will be closed. The valve will move to a right position when v is above 5 V and fully open when v is equal to 10 V. Similarly, the valve will move left if v is less than 5 V and will be fully opened at 0 V. The direction of the air motor depends on whether the voltage v is above or below 5 V. The control input from DSP, denoted by u, will be converted into v as v = u + 5. The major elements of air dynamic system and their functions are listed in Table 1. The experiment results between v and the rotational speed of the air motor is shown in Fig. 3. The signal of u was either linearly increased or linearly decreased by DSP following the cycle 0 V ? 2.5 V ? 2.5 V ? 0 V with a two-second period. The deadzone and hysteretic phenomena were found as shown in Fig. 3. During the increasing procedure, the motor remained motionless when u was set less than 1 V. After exceeding 1 V, the voltage and rotational speed demonstrated near linear relationship. When the voltage was reduced from 2.5 V to 0 V, the speed–voltage relationship did not follow the same curve of rising up but demonstrated a nonlinear behavior. The air motor stopped around 0.8 V instead of 1 V. Similar results were found for u below 0 V. These phenomena were due to the friction in the mechanism and the pressure drop of the supply air at the starting moment. The air pressure was found dropping about 0.8 (kgf/cm2) at the moment of valve opening and returning to its normal values after a short period of time. For instance, if the air pressure was set to 1 (kgf/ cm2), the actual air pressure at the moment of valve opening will drop to 0.2 (kgf/cm2), which was not enough to overcome the static friction and hence caused the delay the system’s response. The efficiency of an air motor is defined as the ratio of the output shaft energy to the input energy of air motor as follows [8]
g¼
Fig. 1. Vane-type air motor.
wT 2pnT ¼ DpQ DpQ
ð1Þ
where w (rad/s) represents the angular velocity of the air motor, Dp (kgf/cm2) represents the different pressure from inlet to outlet of air
Y.-T. Shen, Y.-R. Hwang / Applied Energy 86 (2009) 1105–1110
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Fig. 2. The ideal schematic diagram of air dynamic motorcycle.
Table 1 The equipment of air-powered motorcycle Elements
Function
1 Air tank 2 Filter/lubricant
Store up and provide air Filter the water in the air and avoid the inner of air motor to become rusty. The lubricant will lubricate the air motor Modulate the amount of entering air and control the speed of air motor Calculate the amount of airflow Provide the power Calculate the pressure of airflow Output the analog signal to the electronic control valve
3 Electronic control valve 4 Airflow meter 5 Air motor 6 Pressure sensor 7 Digital controller
g¼
2pnT 2p 2:45 5 ffi 0:4 ¼ 40%: ¼ ðDpÞQ 0:34 583:33
The rear gear assembled on the motorcycle’s rear tire is three time of that of the gear connected to the air motor. This means that the velocity and acceleration of the motorcycle can be obtained by converting the air motor rotational speed and angular acceleration, respectively. For instance, the radius of motorcycle tire is R, the teeth of gear connected to the air motor is Ga, the teeth of gear assembled on the motorcycle’s rear tire is Gt, the air motor rotational speed is wa from the encoder, the motorcycle speed can be calculated as V m ¼ 2pR wa Rg , where Rg ¼ Ga =Gm is the gear ratio between two axes. The data of the air pressure, air flow and the rotational speed of the air motor can be directly measured during the experiment. Therefore, the efficiency of the overall system can be calculated through Eq. (1). 3. Fuzzy control design The experiment results shown that the dead-zone and hysteretic behavior should not be neglected if one wishes to achieve good performance. In order to improve the performance, we implemented a fuzzy logic with PI (proportional integral) control scheme for the air motorcycle system. Two major consecutive steps were designed in this controller. First, we tried to choose best parameters for proportional integral controller only based on the error and its integration as described in Eq. (2)
uðtÞ ¼ kP eðtÞ þ kI
Fig. 3. The relationship between the voltage v and the rotational speed.
motor, T (kgf cm) represents the torque of the air motor, Q (cm3/s) represents the airflow value under compressed condition and n (rps) represents the revolution per second. For instance, if the velocity is controlled at 5 km/h and the different from inlet to outlet pressure of air motor is Dp = 0.34 (kgf/cm2), and the airflow value is kept as Q = 35 (L/min) = 583.33 (cm3/s), n = 2.45 (rps), T = 5 (kgf cm). The efficiency can be calculated as follows:
Z
eðsÞ ds
ð2Þ
As a result of the nonlinear properties of dead-zone and hysteretic behaviors, the selections of kP and kI should be different for different reference speeds and also for different stages of the dynamic responses. Hence, we implemented the fuzzy logic control to improve the system performance. Because the friction and hysteretic behaviors played a significant role when system was at low speed range, the additional control inputs must be considered to compensate these effects. However, these compensations may deteriorate the system performance by introducing large overshoot and chattering. Hence, the compensation should be attenuated once the nonlinear effects become less dominant. At the beginning stage, large kP and kI were required to obtain enough control power to overcome static
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friction and improve the transient response. After the transient period, kP and kI decrease to small values to maintain good performance at the steady state stage. However, sudden switch of kP and kI will deteriorate the performance and result in larger setting time. Hence, we developed the switching rules based on the following fuzzy inference rules
IF E belongs to S~Ei AND D belongs to ~SDi ; ~ belongs to ~S ~p belongs ~S AND k THEN k i kp ki
ð3Þ
where E and D represent error and its variation rate, respectively, ~SEi ~p and k ~ represent and ~ SDi represent the corresponding fuzzy sets, k i the corresponding fuzzy variable of kP and kI, and their corresponding fuzzy sets are represented as ~Skp and ~Ski , respectively. Although one could choose any types of membership functions, the triangle shape functions were used in this paper because of their simpliciSki are shown in ties. The membership functions of ~SEi , ~SDi ; ~Skp and ~ Figs. 4 and 5. The notations in these figures, NL, NM, NS, PS, PM, PL, ZE, etc., represent the fuzzy sets. For instance, NL represents ‘‘negative large”, PS represents ‘‘positive small”, and so on. The ‘AND’ operation of two fuzzy sets ~ SEi and ~ SDi was first proposed by Zadeh [16] as follows:
lEi\ ~ Di ~ ðxÞ ¼ minflEi ~ ðxÞ; lDi ~ ðxÞg
Fig. 7. The road test.
ð4Þ
Fig. 4. The fuzzy membership functions ~ SEi for the error E.
Fig. 5. The fuzzy membership functions ~ SDi for the error rate D.
Fig. 6. The chain connects air motor with rear wheel.
Fig. 8. (a) The velocity of air-powered motorcycle. (b) The velocity of air-powered motorcycle.
Y.-T. Shen, Y.-R. Hwang / Applied Energy 86 (2009) 1105–1110
where lEi ~ ðxÞ and lDi ~ ðxÞ are the degree of membership that E and D SDi , respectively, and lEi\ belongs to ~SEi and ~ ~ Di ~ ðxÞ is the degree of SDi . Another membership that ‘‘E belongs to ~SEi ” and ‘‘D belongs to ~ widely used definition for the ‘AND’ operation on fuzzy sets is the algebraic product, that is
lEi\ ~ Di ~ ðxÞ ¼ lEi ~ ðxÞ lDi ~ ðxÞ:
ð5Þ
In this paper, we adopted the latter definition because of its simplicity and easy for implementation.Defuzzification is the process of converting a fuzzy quantity which was represented by a membership function to a crisp value. The weighted average method is commonly used in industry. It defines the crisp value as the weighted average of membership functions. This method is valid only for the case when the output membership function is a union result of several fuzzy quantities [17]
kx ¼
n X i¼1
, wi kxi
n X
wi
ð6Þ
i¼1
where the index x represents either p or i, and kxi represented the maximum value of ith fuzzy membership functions of ~Skx and wi represented the weighted value of that membership function. Fig. 10a shows the velocity compare to the pressure difference between inlet and outlet. It is shown that if the velocity increases, the pressure difference also increases. The riding speed of the motorcycle is controlled by the driver with a throttle through the controller, which adjusts the electromagnetic valve based on the pressure difference between the inlet and outlet. The fuzzy PI con-
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trol rules are used to determine the control voltage signal to electromagnetic control valve according to the velocity. 4. Assembly and experiment for the air-powered motorcycle A SYM 125 cc motorcycle was modified for this experiment. The four-stroke engine, gasoline tank, carburetor, battery and exhausting pipe of the motorcycle were deprived from the body. At the same time, an air motor, a 10 l air tank (100 kgf/cm2), an air filter and an electromagnetic control valve were installed on the motorcycle. Fig. 6 shows the actual assembly of the transmission system of the air-powered motorcycle. The overall weight, including motorcycle, air tank and driver, is about 150 kg. The practical riding test on the road was shown in Fig. 7. By applying the control algorithm presented in last section, the time histories of the motorcycle speed are shown in Fig. 8a. The speeds were set as from 5 km/h to 30 km/h. It is found that the rising time of all settings are almost the same while the larger acceleration were generated for higher speed setup. Due to the compressibility of the air and the friction of the mechanism, the time delay becomes more obvious for lower speed setup. The final speed errors for all cases are less than 1 km/h. In Fig. 8b, the driver adjusted the throttle from a constant velocity to a higher. The controller can modify the best riding velocity and stabilize it according to the different pressure which was caused by the throttle. As shown in Fig. 9, the efficiency of this system, approximated by a polynomial curve y, increases for larger speed setup and approaches to its maximum around 75%. The efficiency is over 70%
Fig. 9. The efficiency of air dynamic motorcycle, y is a function of polynomial asymptotic curve.
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Fig. 10. (a) The different pressure from inlet to outlet of air dynamic motorcycle. (b) The air flow of air dynamic motorcycle. y is a function of polynomial asymptotic curve.
when the motorcycle’s speed is higher than 20 km/h and does not increase too much for higher speed. The corresponding pressure difference Dp and the airflow Q were shown in Fig. 10. The asymptotic curves of y were almost linear for both cases. These mean that Dp and Q are basically proportional to the speed. The larger speed is, the larger pressure difference and more air flow will be required for the motorcycle. The power source of the motorcycle is a 10 l/100 kgf/cm2 commercial tank, which is refilled by a 7 kW compressor with 75 s. According to the experimental results, with this tank, the motorcycle will run for 2 km for the overall weight of motorcycle as 150 kg. Therefore, the power-consuming for this motorcycle will be about 0.073 kw-hr per kilometer. For a commonly used internal combusting engine motorcycle in Taiwan SYM 125 (10 Hp, 60 km/ h) the consuming power is about 0.127 kw-hr per kilometer. Although the efficiency is higher for the prototype air-powered motorcycle, the transportation distance is not practically enough at the current stage. However, the distance can be increased by equipping a larger volume or higher pressure tank. 5. Conclusion An air-powered motorcycle with fuzzy logic controller has been proposed and tested. The experiment data shows that the speed error of the motorcycle is within 1 km/h and the efficiency is above 70% for this system when its speed is over 20 km/h. The powerconsuming for this prototype is about 0.073 kw-hr per kilometer compared to 0.127 kw-hr per kilometer for a commonly used internal combusting engine motorcycle. Although the efficiency is higher for the prototype, the transportation distance is not enough at the current stage. The future research will be focused on improving
the efficiency and extending the transportation distances for the air-powered motorcycle. References [1] Taiwan EPA,