A Development of Shift Control Algorithm for Automated Manual Transmission in the Hybrid Drivetrain
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Seoul 2000 FISITA World Automotive Congress F2000A036 June 12-15, 2000, Seoul, Korea A Development of Shift Control Algorithm for Automated Manual Transmission in the Hybrid Drivetrain Sungtae Cho1) *, Soonil Jeon1) , Hansang Jo2), Yeongil Park3), Jangmoo Lee1) 1) Seoul National University, Seoul, Korea 2) Hyundai Motors 3) Seoul National University of Technology, Seoul, Korea In this study, a modified shift control algorithm for improving the shift quality of a parallel hybrid drivetrain with an auto- mated manual transmission (AMT) is proposed. Improving shift quality of general AMT demands the sophisticated control for the engagement of clutch, which is generally known to be difficult. But in the parallel hybrid vehicle, both engine and motor can control the speeds of each clutch plate. Therefore it provides the easier clutch control in shift than general AMT. Consequently, it also permits the much reduced shift shock during the shift period. Furthermore various dynamometer- based experiments are carried out to prove the validity of the proposed shift control algorithm. Keywords: Parallel Type Hybrid Drivetrain, Automated Manual Transmission, Shift Control Algorithm The test system for hybrid drivetrain is constructed by at- 1. INTRODUCTION taching motor, inverter, power-connection device, sensor, and actuator and so on to the conventional drivetrain for transit bus. For maximizing fuel economy and minimizing emissions, it is recommended to perform the integrated control of engine, motor and transmission by using an automated transmission. In present days, several automated transmis- sions are developed such as an Automatic Transmission (AT), a Continuously Variable Transmission (CVT), and Automated Manual Transmission (AMT) etc. However there are some limitations to apply an AT and a CVT for heavy-duty vehicles such as transit buses or trucks; AT has the disadvantage of a large amount of power loss as its capacity is increased, and the CVT can be currently ap- plied only for small-sized passenger car. In the case of AMT however, it is easily realized by mounting pneumatic actuators and sensors on the clutch and shift levers of the conventional manual transmission, and it reveals a high 1: induction machine 2: diesel engine 3: transmission efficiency compared with AT, suitable for heavy-duty ve- 4: clutch 5: power connection device 6: inverter hicle. But in the case of heavy-duty vehicle, the shift qual- 7: main controller 8: throttle actuator 9: electric fuel injec- ity of a heavy-duty vehicle is less important than that of a tor 10: battery 11: differential gear 12: wheels passenger car; therefore AMT can be a proper solution for 13-15: x-axis, y-axis, clutch pneumatic actuator a heavy-duty vehicle. ω ω ω 16-18: saw-tooth wheel for mot , eng , veh In this study, the AMT for the hybrid drivetrain for transit Fig.1. Schematic diagram for parallel type hybrid bus is constructed, and an advanced shift control algorithm drivetrain. for improving the shift quality is presented. Adequate con- trols of motor and engine during shift enable the shift shock to be reduced. To verify the presented shift control algorithm, various dynamo-based experiments are carried out. 2. THE HYBRID DRIVETRAIN TEST SYSTEM INCLUDING AUTOMATED MANUAL TRANSMISSION 2.1 THE PARALLEL HYBRID DRIVETRAIN Fig.2. Photo of Hybrid Drivetrain Test Bed. TEST SYSTEM 1 2.2 CONTROLLER 3. SHIFT CONTROL ALGORITHM AND EXPERIMENTAL RESULT The controller, which is designed to manage the overall operation of hybrid drivetrain, is constructed using TMS320C31 DSP Chips. It contains shift logic and power- 3.1 SHIFT CONTROL ALGORITHM split algorithm, so that it controls the velocity and torque of engine/motor.1) (See Fig. 3, 4) Fig.3. Schematic diagram of main control unit. Fig. 6. Flowchart of the AMT control program Fig. 6 shows the basic algorithm applied on the shifting Fig. 4. Photo of main controller and inverter. control of AMT in this study. The shift sequence can be summarized as follows. 2.2 ENGINE THROTTLE CONTROL SYSTEM 1. If the shift starts, the controller separates the clutch plates and simultaneously sets the refer- The integrated control of engine and motor is required to ence torque output of engine and motor. operate them in their high efficiency region. In this study, the vector control method that was applied in the previous 2) 2. After separating the clutch, the gear is shifted to study is used for the motor control, and the engine con- neutral position by the movement of Y-axis shift trol system controlling the throttle of engine was devel- cylinder, and then the speed control starts to syn- oped. In the case of DC motor system for engine control chronize velocities of transmission input/output that in the previous study, there are some problems : the shafts by dc motor. requirement of feedback control, the weakness to the dis- turbance. To overcome those problems, we developed and 3. After the speed control of transmission in- applied the engine throttle control system using step mo- put/output shafts, the gear is shifted to the next tor. Fig. 5 shows the schematic of the engine throttle con- speed by the movement of X-axis cylinder. trol system. 4. During the step of 1-3, the engagement of syn- chronizer is completed, and then the engine speed is controlled to engage the clutch plates. 5. For the speed of input clutch plate to follow the speed of output clutch plate, the speed control of engine is executed. The shift is completed by en- gaging clutch plates after the speed difference between input and output clutch plates is below the reference value. Fig. 5. Schematic diagram of the engine torque control Fig. 7 shows shift sequence in diagram. system using step motor. 2 1. Start shift 3.2 EXPERIMENT OF SHIFT USING BASIC SHIFT ALGORITHM There are 3 modes such as a hybrid, an engine and a motor mode in this hybrid drivetrain. Among them, the hybrid and engine modes show exactly same shift characteristics because they controls power-sources, clutch, and shift mechanism in the same way during the shift. In the case of motor mode, there is negligible shift shock because there is no clutch engagement/disengagement3). So we particularly 2. Separating clutch plates, set the output torque of en- studied the shift characteristics in hybrid mode by experi- ment. gine/motor as zero. And, experiments on 2 ↔ 3 upshift/downshift are carried out because heavy-duty vehicles frequently use upper gear than 2-speed. Fig. 8, 9 show the experimental results of the upshift/downshift that was obtained by applying the basic shift algorithm.4) The large shift shock arises at the moment of clutch en- gagement and right after the shift. In the moment of clutch engagement the minus torque is generated, owing that the 3. Moving the Y-axis cylinder, controlling the speed of speed of the clutch plate connected to engine is lower than motor to engage the synchronizer. that of the clutch plate connected to AMT (Fig.8 (a)-(1), (b)). Fig. 8 (a)-(2) shows the large transient torque generated after shift, the reason is that the controller controls the torque of engine and motor during shift as the reference value, but it suddenly controls them as the driver’s pedal stroke after shift. And the speed difference of clutch plates in engagement is 4. Moving the X-axis cylinder set to the reference value (50, 200rpm) but it wasn’t per- formed perfectly. The reason is that the controller doesn’t compare the reference speed difference with the present speed difference of clutch plates, but it compares the refer- ence with present engine speed. Fig.8 (c) shows that large transient torque is generated right after the engagement of clutch, the reason is that the controller raises the speed of engine rapidly to reduce quickly the speed difference of clutch plates for the en- gagement of clutch. 5. Controlling the engine speed to engage clutch plates. In engaging clutch plates, the speed difference of clutch plates must be reduced within the reference value for the smooth shift by controlling engine speed, but the dynamic characteristics of engine are so tardy, so the overall shift time is prolonged (Fig.8 (b)). 6. Completing shift after clutch is engaged. (a) Torque (upshift). Fig. 7. Schematic diagrams of shift sequence. 3 V) Due to the tardy response of engine, the overall shift time is prolonged. 3.3 IMPROVING SHIFT ALGORHIM THROUGH EXPERIMENT (b) Velocity (upshift). Fig.10 Torque (Upshift) - Experimental result 3 Fig.10 shows the result of a modified shift algorithm in which the controller restores the output torque of engine and motor linearly from the reference value to the value of (c) Torque (downshift). driver’s pedal stroke during 1-second after shift. It shows Fig.8 Experimental result 1 (ref 50rpm engagement) the transient torques after the shift is moderately reduced than Fig.8, 9. Torque (downshift). Fig.9. Experimental result 2 (ref 200rpm engagement). (a) Torque (upshift). The problems of basic shift control algorithm are summa- rized as follows. I) If the speed of the clutch plate connected to engine is lower than that of the clutch plate connected to AMT during the clutch en- gagement, the minus torque is generated. II) In downshift, large transient torque is gener- ated right after the engagement of clutch; the reason is that the controller raises the speed (b) Torque (downshift). of engine rapidly to reduce quickly the speed difference of clutch plates for the engage- ment of clutch. III) Right after the shift, the transient torque is generated, owing that the controller controls torque of engine and motor during shift as the reference value.