| Torque density is the most important performance index to measure the permanent magnet gear.The existing concentric and eccentric permanent magnet gears can achieve larger torque density(concentric is100k N·m/m~3,and eccentric is140k N·m/m~3),so the existing research direction of permanent magnet gear is also mostly concentrated on these two aspects.However,the torque density of the concentric permanent magnet gear decreases with the increase of the transmission ratio,while the rotor bearing of the eccentric permanent magnet gear is located inside the cycloid wheel,which will bear greater unbalanced magnetic tension when working,and greatly shorten the service life of the rotor bearing.In order to solve the above problems,this dissertation proposes a Multishafts Ring-Plate Magnet Gear(MRMG).The MRMG is mainly composed of inner and outer permanent magnet rings and multiple eccentric shafts.The horizontal pendulum movement is formed by multiple eccentric shafts uniformly distributed on the outer permanent magnet ring,which makes the magnetic field force of the inner permanent magnet ring change and then make it rotate with a fixed axis.Because the number of eccentric shaft and its attached rotor bearing is not limited by the number and space size,it has the same torque density as the existing eccentric permanent magnet gear,but also can greatly diffuse the electromagnetic and mechanical force borne by the rotor bearing,and better solve the inherent defects of the above concentric and eccentric permanent magnet gear.Therefore,this dissertation mainly focuses on the following aspects of the proposed MRMG research:(1)The dynamic model diagram of MRMG with feedback mechanism is established to intuitively express the relationship between MRMG dynamic torque and speed.By feedback the magnetic deflection angle of each dynamic process,the rotation angular velocity of the inner permanent magnet ring and the revolution angular velocity of the outer permanent magnet ring are associated with the electromagnetic torque,the loss torque,and the action load between the ring plate and the rotor bearing.All the physical quantities of MRMG can be expressed as single-valued functions of magnetic deflection angle,so as to quantitatively analyze the dynamic process of MRMG start-up process and stable operation process,and then reveal the operation mechanism of MRMG with large transmission ratio and high torque density in essence.(2)Based on the scalar magnetic potential method,the inner and outer permanent magnet rings of MRMG are divided into a non-source region and two source regions.The two source regions are related by the continuity of the air gap magnetic field.The magnetic field boundary conditions are combined with the magnetic field superposition principle to obtain the two-dimensional magnetic field and electromagnetic torque mathematical model of MRMG.Although the 2-D model based on the planar magnetic field can quickly calculate the air-gap magnetic field and electromagnetic torque of MRMG,the 2-D model ignores the magnetic end effect,so the obtained results deviate from the actual results(the error is about17%).Therefore,a 3-D mathematical analytical model including the magnetic end effect should be established to accurately calculate the air-gap magnetic field and electromagnetic torque of MRMG.(3)The influence of structural parameters of MRMG on electromagnetic torque is analyzed by comprehensive sensitivity method,and the influence of relevant structural parameters such as long side length,short side length,axial length and minimum air gap of the permanent magnet on the maximum static electromagnetic torque and torque density is given by using the prediction model.Then the parameters of the inner and outer permanent magnet yoke iron and the thickness of the permanent magnet are scanned and optimized by the finite element method to determine the appropriate parameter optimization values.(4)According to the moment of momentum and kinetic energy theorem,the starting process of MRMG at different starting positions is qualitatively and quantitatively analyzed.The dynamic speed and torque and the relationship between forward and reverse impulse formed by deeply analyzed when MRMG is started at different positions,so as to determine the best starting interval and starting position of MRMG.Since the inner and outer permanent magnet rings will also produce speed and torque oscillation and self-adjust when MRMG is overloaded,the forward and reverse impulse relationship generated by the outer permanent magnet rings s after MRMG recovers from overload to normal load is analyzed,and dynamic simulation verification of constant load and variable load is carried out by finite element method.Finally,the conditions under which MRMG can be restored to normal operation after overload are determined.(5)The motion process of the inner and outer permanent magnet rings is discretized as the relationship between magnetic declination angle and static electromagnetic torque,and the mathematical model of MRMG dynamic torque and rotational speed can be established.Because the built model contains mechanical losses of the boom bearing that cannot be accounted for by the finite element simulation,the calculated speed ratio,torque ratio and transmission efficiency are more close to the dynamic measured results(the model error is less than 2%,while the finite element error is about 6%).(6)According to the power distribution characteristics of MRMG,the balance relationship between the inner and outer permanent magnet rings with each transmission shaft and the transmission loss characteristics are established by combining the MRMG electromagnetic torque model with the rigid body static theory,and analyze the mechanical stability and power loss of the"single input/single output"and"single input/multiple output"transmission modes.Among the two transmission modes,the operation characteristic when each eccentric shaft under the same load is the best(operation efficiencyη=92.76%),followed by the mode when each eccentric shaft bearing under the deviating load(η=83.67%),and the"single input/single output"mode is the worst(η=68.38%). |
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