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Research on Optimum Design and Simulation of Gear Reducer inElectric Steering EngineF.C. Tao 1,a , J. Liu 2,b ,G.L. Wang 2,C and Y. Shi 3,d1School of Mechanical & Power Engineering, Harbin Univ. of Sci. and Tech., Harbin 150080, China 2School of Mechanical & Electrical Engineering, Harbin Institute of Technology, Harbin, China 3Harbin National Investment Project Evaluation Center & Harbin International EngineeringConsulting Center, Harbin 150080, Chinaa taofuchun-001@,b liu_hit@, C ghwgl@, d shiyuhome@ Keywords: Gear reducer, Optimum design, Mechanism simulation, Electric steering engineAbstract. Electric steering engine was generally applied in arm systems such as carrier rocket and missile, its life period is very short, and the space and weight of its reducer were strictly restricted, so it is not fit to adopt the conventional rule of infinite life to design electric steering engine gear reducer. This paper carried out the optimum design for it based on the rule of finite life and space, provided and demonstrated a new design scheme, and realized the interior overall structure design of reducer. We used the UG plane to realize three-dimension module design and virtual assembly of gear reducer, elaborated the implementation method of three-dimension motion simulation by the parameter drive mechanism, and simulated the actual working procedure. Experimental results indicated that this gear reducer satisfied excellently the requirement of big drive ratio under the finite life and space.IntroductionThe space and weight of electric steering engine reducer was generally strictly restricted, and it must transfers very big torque under finite space and weight and its service life is very short, in most operation of the reducer, it was used only one time. At present, in the gear reducer design, the conventional method based on the rule of infinite life and reliability, and selected the surface fatigue failure or root fatigue damage as failure mode of parts to checking calculation [1, 2], however, the space of gear reducer which was design by this conventional method is too big to the special demand of electric steering engine in actual application, so it is necessary to adopt a new reducer design rule according to the characteristic of electric steering engine, which is the rule of finite life and space. In addition, the gear reducer was composed of many parts, and the assembling scheme is various, so it is very necessary to calculate and demonstrate the feasibility of each assembling scheme. This paper elaborated and analyzed the optimum design and calculation and checking of electric steering engine gear reducer under the rule of finite life and space, and the three-dimension modeling, virtual assembling, and motion simulation of gear reducer by UG plane.Structure Optimization Design of Gear ReducerAccording to outline dimension requirement in the special design program of electric steering engine mechanism, the input shaft of electric steering engine and the output of gear reducer are vertically crossed, the drive ratio was estimated about 420 according to the given technical parameters, so it was required that the gear reducer must has small space, big drive ratio, light weight. Because of very small space, it is impossible to realize the multistage drive, and in the light of vertical crossing between input shaft and output shaft, the gear reducer must has a bevel gear which can change the drive direction of shaft, however, the drive ratio range of bevel gear is very finite, so the designed reducer has two level drive. The bevel gear was set as high speed level, its drive ratio was tentatively assigned as 3 based on the space requirement and drive characteristic, sodrive ratio, it includes the harmonic gear drive and the cycloidal needle gear drive. The harmonic drive has many merits such as simple structure, small space, light weight, bit drive ratio range, excellent load-carrying ability, non-impact, smooth movement and high drive efficiency [3]. Considering the space of gear reducer, machining technology and cost, speed range of input shaft, and adjusting range of drive ratio, we adopted the double wave drive which is used widely in harmonic drive, and set the harmonic generator as primary member, the flexible wheel as driven member, the rigid wheel as built-in member.The bevel gears whose axis are orthogonal were adopted as high speed level, the outside diameter of small bevel gear is not permitted toexceed16mm, it is difficult to machine, so it is required that bevel gear is not sensitive for installation error and deformation. In addition, it is required that the output speed can achieve 4200 r/min, and the bevel gear drive has the excellent motion stationarity and high accuracy, so we chose the Gengenbach cycloid gear as the high level. Structure design of electric steering engine gear reducer is shown in Fig. 1.1.Small bevel gear2.Barrel3.Left head cover4.Assembly of harmonic generator5.Gasket6.Shell(rigid wheel)7.Flexible wheel8.Right output shaft9.Right head cover10.Resetting shaft 11.Pad 12.Head cover 13.Barrel 14.Cover plateB1.Rare earth permanent-magnet DC motor B2.Screw B3.Deep groove ball bearingB4.Screw B5.Deep groove ball bearing B6.Screw B7.Deep groove ball bearing B8.ScrewFig. 1 Structure design scheme of electric steering engine gear reducerAccording to the structure design scheme, we adopted the optimum design method to design and calculate, and obtained the optimum parameters. In this design, electric steering engine gear reducer has obvious requirement for space, so the smallest space was selected as the objective function to optimization based on the rule of finite life and space. In order to simplify the calculation, we mainly optimized and calculated the harmonic gear, and adopted the modulus m , the length of flexible wheel barrel l , the breadth of tooth b , and the barrel wall thickness δ as optimization variable, the smallest space of flexible wheel and the biggest drive efficiency as design target. The bound of objective function includes abrasive tooth wear, stable condition of flexible wheel barrel, and endurance strength and crushing strength of gear, and it realized the multiple objective optimization design of harmonic gear by this optimum design method.Motion Simulation of Gear ReducerFor the designed harmonic gear reducer of electric steering engine, in order to analyzing structure and motion and optimizing design, it was required building a numeric prototype which is same asdesign mechanism and develop new product, realize parameter drive, automatically check interference and gap, and automatically generate engineering graphic, we used the UG plane to realize the function mentioned above. The general scheme of gear reducer three-dimension motion simulation using the UG plane is shown in Fig. 2.Fig. 2 General scheme of gear reducer three-dimension motion simulationThree-Dimensional Model Building and Virtual Assembling. Aimed at the characteristic of each kind of part in gear reducer, we built the scanning body by stretching or revolving draft curve, and used the character tools provided by UG which includes basic body “Cone”, “Sphere”, “Cylinder”, and the characteristic “Hole”, “Groove” to realize solid modeling of each part. And then we assembled reducer by assembly module. The process using UG to assemble is to simulate actual assembling work, and the key point is to choose the assembling type. Firstly, we assembled the scattered parts as sub-assembly, and then assembled the each sub-assembly and related parts to obtain the whole reducer module. Firstly, we added related part in turn according assembly subsequence to UG assembly plane, and adjusted the position relation of each part by the option “Reposition”, and then used the allocation option “Mate”, “Align”, “Perpendicular”, “Parallel”, “Centre”, “Distance”, and “Tangent” to realize the virtual assembling by the mode of “from top to down”. For the gear, it is impossible to directly engage if it didn’t has shape condition which is need by the three bondage—“Mate”, “Align” and “Orient”, so we need to build reference plane individually on two gears. We chose a random point on cutting pitch circle of gear involute, and built a reference plane through the point which was against to normal direction of tooth profile. We also set a reference plane on the cutting pitch circle of wheel tooth for another engage gear, and set corresponding relation for the two reference plane, so it realized the engage of the two gears. Finally, it is necessary to check the mechanism assembly effect, and then modify and consummate the assembly model, which is shown in Fig. 3. In addition, we generated the explosion diagram and corresponding two-dimension engineering graphic, and it was convenient to interior structure and space cast relation of reducer assembly. The explosion diagram of gear reducer is shown in Fig. 4.Fig. 3 Assembly diagram ofgear reducerFig. 4 Explosion diagram of gear reducerThree-Dimensional Motion Simulation of Gear Reducer . After assembling the each part of harmonic gear reducer, it is necessary to check motion trace and motion interference of each part, analyse and verify the parameters of parts such as velocity, accelerated velocity, applied force, reacting force and torque, furthermore, judge feasibility of gear reducer design and motion. Beforemotion unit according to the mark subsequence using the option “Link” in the module “Motion”, and generated various con-rod by drive relation, and then defined the kinematics pair between each unit using the option “Joint” which included “Revolute”, “Slider”, “Cylindrical”, “Gear” and so on. After defining each kinematics pair, we adopted the option “Animation” to calculate accuracy of mechanism loading motion, and then the mechanism assembly of gear reducer was initiated to start three-dimension motion simulation, and interference analyse, kinematics analyse and kinetics analyse for motion simulation. For example, using the function of “Interference” in the option “Animation” to check the motion interference, and marking the point in the mechanism by the option “Maker/Smart Point” to acquire the parameter in motion simulation such as velocity, accelerated velocity and so forth. Interior schematic of motion simulation by UG plane is shown in Fig. 5.Fig. 5 Interior schematic of motion simulation by UGConclusionsThe harmonic gear reducer designed in this paper adequately considered the operation requirement of electric steering engine, and a new design method of gear reducer was provided based on finite life and space. We used this method to carry out the optimum design, calculation and checking for each component of gear reducer, and realized big drive ratio which guaranteed the maximum output torque of electric steering engine, in addition, used the UG plane to realize virtual assembly, interference checking and mechanism motion simulation for harmonic gear reducer of electric steering engine, and it increased the design accuracy, reduced the possible mistakes in manufacturing procedure and guaranteed the reliability of gear reducer design.References[1] H. Haruo, U. Kiyohicko and M. Shigeki: ASME Power Transmission and Gearing Conference,Vol. 88 (1996), pp. 501.[2] Y.C. Tsai and W. K. Jehng: Mechanism and Machine Theory, Vol. 34 (1999), pp. 857.[3] J. Zhang, Y.M. Song and C. Zhang: Transaction of Tianjin University, Vol. 13 (2006), pp. 163.[4] O. Vogel, A. Grewank and G. Bar: Computer Methods in Applied Mechanics and Engineering,Vol. 191 (2002), pp. 3965.Manufacturing Automation Technologydoi:10.4028//KEM.392-394Research on Optimum Design and Simulation of Gear Reducer in Electric Steering Enginedoi:10.4028//KEM.392-394.767。