Economic Hybrid Transmission System using Clutchless Geared Manual Transmission

EVS28 KINTEX, Korea, May 3-6, 215 Economic Hybrid Transmission System using Clutchless Geared Manual Transmission Huiun Son, Yong-San Yoon, Kyung-Soo Kim, Sun Je Kim, Chiwoong Song Mechanical Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 35-71, Korea Abstract In this study, we are proposing a hybrid car of new concept promising the most economic and fuel efficient one. The architecture is derived from the conventional manual transmission with little modification by replacing the clutch with the one-way clutch and a motor-generator is placed between the one-way clutch and the gearbox. Another addition is the motion detector of the gear-shift lever that the vehicle may recognize which is intended to engage by the driver. The advantages of the this new hybrid vehicle compared to other hybrid vehicles are as follows. Firstly, the drivetrain is composed of the most economic components in simplest way just by serially attaching a motor-generator to the conventional manual transmission. Secondly, the drivetrain consumes minimum amount of energy as it doesn t requires any additional actuator to control in addition to its light weight as well as the efficiency of the manual transmission. Thirdly, as the conventional clutch is eliminated and the motor-generator is assisting the gear synchronization, the operation of the gear shift is almost as easy as the automatic transmission. Fourthly, as the gear shift is performed by the driver, the driver may avoid the situation of the unwanted gear shift which may happen in the automated manual transmission. Additionally, the gear shift process takes half the time required by the automated manual transmission as there is no clutch. A prototype of the hybrid drivetrain named as the clutchless geared manual transmission (CGMT) is adopted to a small vehicle (Chevrolet Damas, 796cc, 5 speed manual transmission) adding a 7KW electric motor-generator in series. The vehicle is designed such that it may run only by the motor-generator when the vehicle speed is less than 4 kph with the engine being shut-off. Some test results will be presented. Keywords: Hybrid, Manual Shift, Clutchless, Economic, Simplest architecture 1 Introduction The most important part of a car is the powertrain that delivers power from the power-source to the wheels. Among the main components of the powertrain, a transmission, especially, highly affects to the cost, gas-mileage, and convenience. As the technology of engines has been fully matured, the study for transmissions has become much more promising. There are various types of transmissions; manual transmission (MT), automated manual transmission (AMT), automatic transmission (AT), EVS28 International Electric Vehicle Symposium and Exhibition 1

dual clutch transmission (DCT), continuous variable transmission (CVT), etc. MT is the cheapest one and has good gas mileage. However, difficulty of the clutch actuation is critical barrier to expand its share even though its great efficiency. To solve inconvenience of clutch, an actuator controls the clutch in case of the AMT. Due to nonlinearity of clutch comes from temperature, humidity, etc., many sensors are needed. The control is based on characteristics curve so that the more probability of control failure as a clutch has worn out. Moreover, after engaged neutral gear, transmission speed is oscillating. The amplitude of the oscillating transmission speed and the time delay are higher the higher the stationary speed is [1]. Consequently, it is difficult to control in particular situations like bump, curve, etc., and it cannot shift rapidly.for such a reason, the market share of AMT in light vehicle is less than 1 % in 212 and the estimation in 217 is still less than 1 % [2]. AT has relatively small shifting impact using a torque converter. However, the AT has low efficiency due to the fluidic resistance. Also, in view of shifting quality, unexpected gear shifting or little delay of driver s acceleration will give the driver displeasure feels [3]. DCT uses two clutches; for even gears and for odd gears, and it can accomplish fast and smooth gear shift without torque gap by engaging the clutches simultaneously. It is not only comfortable but also gives good gas-mileage. However, it is still expensive, and needs advanced clutch control by using hydraulic actuators [4]. Moreover, because smaller clutches is necessary due to two clutches in same space, torque allowance is reduced by small friction surface of clutches [5]. CVT makes an engine operate in optimal range, however, it has similar gas mileage of the AT due to slippage of belt and operation of hydraulic actuators. Also, it cannot deliver high torque to wheels [6]. In the case of a hybrid vehicle, new concepts of transmission using an electric motor are suggested [7]. For the Toyota, by using concept of power-split, two electric motor/generators increase the price of the vehicle [8]. The Zanhrad Favrik (ZF) uses friction clutch in hybrid power train so that increase in price and weight is expected [9]. To solve these limitations of existing transmissions, the clutchless geared manual transmission (CGMT) was proposed. Instead of a clutch of the manual transmission, an electric motor is used for CGMT to perform a gear shift so that much faster and more exact control than automated manual transmission is possible. Consequently, robustness is guaranteed in special situations like bumps or curves. This novel gear shift mechanism can provide easier operation for novices. Also, the motor is utilized as the hybrid system to have improved gas-mileage. Based on manual transmission, in addition, a small amount of additional cost for adopting the CGMT. In this research, the feasibility of CGMT was verified. In section 2, the operating principle of CGMT is explained. The development of prototype is introduced in section 3 and the verification experiment is described in section 4. In section 5, experiment results is shown. Finally, conclusions is formed in section 6. 2 The operating principles of the CGMT 2.1 Mechanism of the manual transmission To understand the fundamentals of CGMT, basic knowledge about a manual transmission is necessary. Figure 1 shows a structure of manual transmission. The input-shaft is connected to the engine, and the input-gear transfers the engine power to the counter-gear. All counter-gears which are on the lay-shaft and the lay-shaft are connected so that all counter-gears transfer engine power to the output gears. The output-gears on the outputshaft, however, are not connected to the outputshaft. The output-gears is idling without providing traction force on the output-shaft in neutral condition. The synchronizer is connecting element to engage the output-gear and the output-shaft, simultaneously via the synchronization of frictional cone and sleeve. The output-shaft finally transfers the power to wheels. However, synchronizers cannot normally work while engine power flow exists. Thus, the clutch is normally used to cut off the engine power during Figure 1: Structure of the manual transmission [1] EVS28 International Electric Vehicle Symposium and Exhibition 2

Figure 2: Structure of the CGMT shifting gears. After engaging the synchromesh, a clutch synchronizes the engine speed and inputshaft speed. However, shifting gear is possible without clutch operation. The output-gear which will be shifted and output-shaft can be synchronized by elaborate control of accelerator pedal. Similarly, instead of clutch, motor synchronizes the outputgear and the output-shaft in case of CGMT. 2.2 Mechanism of the CGMT 2.2.1 Modification from the manual transmission In CGMT, because all the gears, input-shaft and lay-shaft are always connected each other, the motor can be connected to any one of these components. However, considering the capacity of engine room and leakage problem of transmission-oil, the electric motor/generator of the CGMT is connected to input-shaft as shown in Figure 2. The motor can synchronize the speed of the output-gear during shifting gears, and also perform common hybrid functions such as regenerative braking and assisting engine to operate in optimal range. The sprag-clutch replaces the friction clutch of the manual transmission. A sprag-clutch is a oneway freewheel clutch such as a rear wheel of bicycle. Using this sprag-clutch, the engine power cannot be transferred to the transmission when motor is faster than engine. Using idle stop and go (ISG) system, start the engine after motor is faster than engine idle speed and turn off the engine before motor is slower than engine idle speed to prevent engine died. This component is advantageous in city-drive that includes frequent stop and go. 2.2.2 The operating principles At the start stage, only the motor transfer power to the wheels to start. When the motor speed is faster than the engine idle speed, the engine is turned on and the engine provides the propulsion power. Figure 3: The motion detector of gear-shift lever To shift to higher gears, the driver steps off the acceleration pedal, and engine torque is cut off. Next, the motor synchronizes the output-shaft and out-put gear. After synchronization, the driver can shift gear. The shifting mechanism of lower gears is the same as that of shifting to higher gears. During the stopping process, before the motor speed is lower than the engine idle speed, the engine is turned off. 2.2.3 The motion detector of gear-shift lever The motion detector of gear-shift lever using halleffect sensors was installed. The motion can be detected by sensing the magnetic force while actuating the lever as shown in Figure 4. The lever is supported by ball-socket joint so that the sensors should be placed on the surface of concentric sphere. 3 Prototype development The prototype of the CGMT was developed using a typical compact vehicle (Damas by Chevrolet, 796 cc engine with 28 kw power) and an electric motor (7 kw electric motor), and a 5-speed manual gearbox. The electric motor can cover 4 km/h of the vehicle speed without engine support. Detailed information is shown in Table 1 and Table 2. The schematic of CGMT is shown in Figure 4. The control unit is based on the DSP TMS32F28335 microprocessor to get information of engine RPM, motor RPM, output-shaft RPM Figure 4: Hybrid transmission system using CGMT EVS28 International Electric Vehicle Symposium and Exhibition 3

Table 1: Converted vehicle overview Name Engine displacement Fuel Maximum power Maximum torque Layout Transmission Maximum speed Vehicle weight Damas, Chevrolet 796 cc LPG 28 kw 62.8 N.m FR 5-speed manual 115 km/h 87 kg Table 2: Electric motor/generator specifications Name AMDM41 Maximum power 2 kw Maximum torque 92.2 N.m Rated power 7. kw Rated speed 265 RPM Bandwidth 9Hz and selected, and to control the motor torque during shifting gears. Instead of the clutch of a manual transmission, the electric motor synchronizes the speed of the output-shaft and the output-gear which will be selected, and then the gear can be smoothly engaged without clutch operation. This novel gear shift mechanism can provide easier operation for novices. When the shift to the third step, the engine is turned on by using ISG system that is operated by the DSP. 4 Experiments method Indoor tests was conducted using the prototype of the CGMT. For indoor tests, the moment inertia of the vehicle (about 75 kg.m 2 ) was replaced by the custom-built inertia and it is connected to the rear wheel. Step-by-step gear shifting scenarios were conducted. Various scenarios will be tested on a paved road. Not only normal conditions but also unique conditions will be considered, such as parking, uphill, downhill, speed bump, curve, etc. 2 15 5 2 18 16 14 12 8 6 4 2 motor rpm 5 1 15 2 25 3 Figure 5: Working process - departure motor rpm 38 4 42 44 46 48 5 52 54 56 Figure 6: Working process shifting to upper gears 2 motor rpm 18 16 14 12 8 6 4 2 6 62 64 66 68 7 Figure 7: Working process shifting to lower gears 2 motor rpm 18 16 14 12 8 6 4 Figure 5: Connection of custom-built inertia 2 38 4 42 44 46 48 5 52 54 56 Figure 8: Working process - stop EVS28 International Electric Vehicle Symposium and Exhibition 4

5 Results The sifting time was measured through the motion detector of gear-shift lever. It takes an average of 1 to 2 seconds to shift. Considering human gesture that is took about.3 seconds, synchronization should be finished in.3 seconds for smooth operation. Figure 5 shows the test results of the departure. Gear step is displayed by multiplying by 1 and means that neutral gear is engaged. When is, it means the state in which the engine is off. When it is 2, the engine is turned on. The vehicle was starting in the second gear. At first, only the motor transfer power to the wheels to start. The engine remains off. After neutral gear is engaged to shift the third gear, the motor synchronizes the output-shaft and outputgear and the engine is turned on. After synchronization, the driver can shift gear. After the third gear is engaged, the engine can add power. Target rpm is meaningful only when the neutral gear is engaged. The process of shifting to gears is shown in Figure 6 and Figure 7. To shift to higher gears, the driver steps off the acceleration pedal to cut off engine torque and shift to neutral. Then, the motor synchronizes the output-gear. After synchronization, the driver can shift gear. The shifting mechanism of lower gears is the same as that of shifting to higher gears. Figure 8 shows the process of stop. During the stopping process, before the motor speed is lower than the engine idle speed, the engine is turned off. 6 Conclusions The interactive hybrid transmission system using CGMT was suggested. Not only low price, but also great improvement on gas-mileage are expected as a hybrid transmission. Instead of clutches, smooth gear shifting can be accomplished by motor control. Despite the motor was chosen arbitrarily, it was tracking output-shaft speed well during the shifting period. Also, the speed change of the output-shaft is intense than the actual because the custom-build inertia is far lower than actual vehicle inertia, so that better test results of the vehicle driven on the road is expected. Consequently, Operational feasibility of the CGMT was proven. In future works, various control method will be applied. And, optimal design will be searched with considering engine brake, performance in low step. Through system modelling, improvement of fuel efficiency will be also showed. Acknowledgments This research was supported by basic science research program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (213R1A1A25911). References [1] Pettersson, Magnus, and Lars Nielsen., Gear shifting by engine control, Control Systems Technology, IEEE, Vol.8, No.3 (2), 495-57. [2] Statista, http://www.statista.com, accessed on 214-9-1. [3] Byeonguk Jeon., Introduction of Quantitative Measuring Methods for Objective Shift Quality Evaluation, Journal of the Korean Society of Automotive Engineers, Vol.35, No.8 (213), 16-24. [4] Lee-Hyung Cho, Seibum Choi., A design of sliding mode controller for shift performance improvement of Dual Clutch, KSAE 27 Autumn Conference, Vol.2 (27), 975-981. [5] Kulkarni, Manish, Taehyun Shim, and Yi Zhang., Shift dynamics and control of dual-clutch transmissions, Mechanism and Machine Theory, Vol.42, No.2 (27), 168-182. [6] Dongwoo Kim, Hyunsoo Kim., Shift Control Strategy for Electric Controlled CVT vehicle, The Korean Society of Automotive Engineers (KSAE), Vol.8, No.3 (2), 85-97. [7] Sun Je Kim, et al., Verification of the Shifting Mechanism of Clutchless Geared Smart Transmission using the Compact Car Size Test Bench, Vehicle Power and Propulsion Conference (VPPC), 213 IEEE(213), 1-5. [8] Liu, Jinming, Huei Peng., Modeling and control of a power-split hybrid vehicle, Control Systems Technology, IEEE Transactions on 16.6 (28), 1242-1251. [9] Reed, Jr. et al., Method of Converting an Existing Vehicle Powertrain to a Hybrid Powertrain System, United States Patent, US 6332257 B1 (21). [1] Howstuffworks, http://auto.howstuffworks.com/, accessed on 214-9-1. EVS28 International Electric Vehicle Symposium and Exhibition 5

Authors Huiun Son received the B.S. degree in Mechanical Engineering from KAIST in 214. He is currently working toward M.S. degree at KAIST. His research interests include propulsion systems for hybrid vehicles. Yong-San Yoon received his PhD degree from the Univ. of Iowa in 1979. Currently, he is a professor emeritus of Mechanical Engineering, KAIST and involves in the several projects of developing new derive trains. Kyung Soo Kim received the B.S., M.S., and Ph.D. degrees in Mechanical Engineering from KAIST in 1993, 1995, and 1999, respectively. He was Chief Researcher with LG Electronics, Inc., from 1999 to 23 and a DVD Group Manager with STMicroelectronics Company Ltd., from 23 to 25. In 25, he joined the Department of Mechanical Engineering, Korea Polytechnic University, as a Faculty Member. Since 27, he has been with the Department of Mechanical Engineering, KAIST. He serves as Associate Editors of Automatica and Journal of Mechanical Science and Technology. His research interests include the control theory, sensor and actuator design and robot manipulator design. Sun Je Kim received the B.S., M.S. and Ph.D. degree in Mechanical Engineering from KAIST in 29, 211 and 215 respectively. His research interests include propulsion systems for hybrid vehicles. Chiwoong Song received the B.S. and M.S. degree in Mechanical Engineering from KAIST in 2 and 2 respectively. His research interests include propulsion systems for hybrid vehicles using flywheel. EVS28 International Electric Vehicle Symposium and Exhibition 6