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Introduction Gear motor has the advantages of simple structure, small size, light weight, small moment of inertia, easy manufacture, low price and strong anti-pollution ability. It has been widely used, but the traditional one-piece gear type is only open. The external gear motor has disadvantages such as large output speed and torque ripple rate and small starting torque. In order to improve the performance of the gear motor, a balanced compound gear motor with four external gears and one internal gear structure has recently appeared. This type of motor has large output torque, small pulsation rate of output speed and torque, and radial force. Balance and other outstanding advantages, but its structure is more complex, manufacturing precision requirements, manufacturing difficulties, high manufacturing costs, is not conducive to popularization; this paper studies a three-gear motor with two idle gears and a torque output gear, proposed Its structure type, discusses the working principle, analyzes the radial force of the gear, the output angular velocity and the torque characteristics, and clarifies its superior performance and the conditions it should meet. It is intended to obtain a superior performance and a simple structure. The gear motor is easy to design and manufacture, with a view to attracting the attention of the industry and facilitating its promotion.
1Structure principle This kind of motor is mainly composed of left and right end covers, housing, two idle gears, torque output gears, shafts, keys, sliding bearings, etc. The center gear (torque output gear) and two idle gears respectively form two External gear motor (sub-motor); the inlet and outlet ports of the two sub-motors are separated in the housing, and two pairs of oil inlet holes and oil outlet holes are opened on the end cover, and are connected by pipes, and then integrated into a total The oil inlet and the oil discharge port communicate with the outside world. When the pressure oil is input from the oil inlet port, the unbalanced liquid pressure acts on the tooth surface of each gear (the same way as the ordinary gear motor), and then the driving torque is generated to the center of rotation of the gear, and the gear is pushed in the direction shown in FIG. Rotation, as the gear rotates, the hydraulic oil is carried from the high pressure side to the low pressure side, and then discharged through the drain pipe. When the gear rotates, the speed and torque are output outward to overcome the load moment of the working mechanism and make it operate. The output torque of the motor should be the superposition of the hydraulic torque generated by the three gears, and the output speed is the same as the speed of the sun gear. Since the three gears are located on the same plane, the two sub-motors composed of the two idle gears and the torque output gears are independent of each other, the oil inlet port and the oil outlet port are connected in parallel, and share an axial external output speed and torque. Therefore, it is called a planar parallel gear motor. The gear motor can be connected by external pipeline connection, no special distribution device is required, and the structure of the ordinary gear motor is very similar (also adopts three-piece structure), which is convenient for design, manufacture, installation and use. It can be seen that the motor retains the advantages of simple structure, easy manufacture and low price of the ordinary gear motor.
2 Performance analysis studies the use of a standard involute gear motor with the same number of teeth and gear parameters and an overlap factor greater than one.
2.1 Radial force According to the structural principle, the radial force acting on the motor torque output gear and the idle gear is different.
2.1.1 Torque output gear The oil inlet and outlet of the motor are symmetrically arranged on both sides of the torque output gear. The gear parameters and working conditions of the two sub-motors are also the same, so that the hydraulic output force of the torque output gear is Completely balanced with the meshing force, that is, the resultant force of the radial force acting on the torque output gear is equal to zero, because the torque output gear is subjected to a large load, this advantage has a particularly important significance, which can significantly reduce the gear shaft and bearing Wear, extend its working life and improve the reliability of the motor.
1. Motor body; 2. Right end cover; 3, 8, 9. Bushing; 4, 10. Freewheeling gear; 5. Torque output gear; 6. Key; 7. Output shaft; 11. Left end cover 2.1.2 Freewheel gear Because the structure and working principle of each sub-motor is the same as that of the ordinary external gear motor, the bearing condition of the idle gear is the same as that of the ordinary gear motor, and it is still subjected to the unbalanced radial hydraulic pressure and the meshing force, and the synthetic path acting on each gear. The force can be approximated by the following formula: F2=F3=8.5pBDe(1) where: De is the diameter of the tip circle, mm; B is the tooth width, mm; p is the pressure difference between the motor inlet and outlet, MPa.
The number of teeth of the planar parallel gear motor is z1, the diameter of the tip circle is De1; the number of teeth of the ordinary gear motor is z2, the diameter of the tip circle is De2, the modulus is the same as the tooth width, and the output torque is equal under the same working pressure. When the displacement of the two motors should be equal, according to this, z1=12z2(2)De1≈12De2(3), that is, under the same output torque, the diameter of the tip circle of the motor is reduced by about half compared with the ordinary gear motor. The radial force is also reduced by nearly half, and the radial force experienced by the idler gear is also greatly reduced.
2.2 Output speed and torque 2.2.1 Theoretical average speed Since the motor is composed of two sub-motors, the displacement is doubled at the same number of teeth, so the angular speed is reduced compared to the ordinary gear motor when the input flow and gear parameters are the same. Half of it is good for improving the low speed stability of the motor. If you want to get a higher speed, you should increase the input flow.
2.2.2 Theoretical average torque When the pressure and gear parameters are the same, the displacement is doubled, and the output torque is doubled compared with the ordinary gear motor, thus obtaining a large starting torque and improving the starting performance.
2.2.3 Theoretical instantaneous angular velocity There is a large pulsation of the instantaneous output rotational speed of the ordinary gear motor, mainly due to the change of the meshing point relative to the node (the meshing point distance) during the gear running. For the planar parallel gear motor, There are two sub-motors working at the same time, the difference of the meshing point distance is different, the instantaneous angular velocity of each independent output will be different, but they share one output gear, only one instantaneous angular velocity, because the gear shaft has elasticity, the instantaneous angular velocity should be It is the superposition of the instantaneous angular velocity of the two sub-motors; since the structure of the motor is basically the same as that of the two driven wheel-type compound gear pumps, the working principle is reciprocal, and the magnitude and phase change of the meshing point moment should be the same, and the calculation formula of the instantaneous angular velocity can be The calculation formula of the instantaneous flow rate of the second driven wheel type compound gear pump is derived from Qsh=Bsh[2(2Rh' h'2)-(f21 f2)]=2Bsh[R2e-R2-12(f21 f2)](4 ) can obtain sh = Qsh2B [R2e-R2-12 (f21 f2)] (5) where: Qsh is the input flow of the motor; h' is the top of the tooth; f1, f2 are the meshing point distance of the two sub-motors.
That is, the theoretical instantaneous angular velocity of the motor is also reduced by half, and varies with the meshing point distance, and there is pulsation.
2.2.4 Theoretical Instantaneous Torque The theoretical instantaneous torque of a common gear motor also varies with the change of the meshing point distance. The theoretical instantaneous torque of each submotor is obtained by the literature [1] as Msh1=M1 M2R1R2=12Bp[2R1( H'1 h'2) h'21 R1R2h'2-(1 R1R2)f21](6)Msh2=M1 M3R1R3=12Bp[2R1(h'1 h'2) h'21 R1R3h'23-(1 R1R3) F2] (7) The total theoretical instantaneous torque of the motor is M'sh=Msh1 Msh2=2M1 M2R1R2 M3R1R3=2Bp[2Rh' h'2-12(f21 f2)](8) where: M1, M2, M3 respectively For the hydraulic torque acting on each gear; R1, R2, R3 are the pitch radius of each gear; h'1, h'2, h'3 are the tooth tips of each gear respectively; when the number of teeth and gear parameters are equal, M1 =M2=M3, R1=R2=R3, h'1=h'2=h'3=h'.
It can be seen that the instantaneous output torque of the motor also varies with the meshing point distance, and there is also pulsation.
2.2.5 Quality Analysis of Speed ​​and Torque The instantaneous output speed and torque of the gear motor vary with the distance between the meshing point and the joint (the meshing point distance), and the change of the meshing point distance is caused by the gear meshing. The characteristics of the transmission are determined inevitably. Therefore, for a common gear motor having only a pair of gears, the large output speed and the pulsation of the torque become inevitable. However, for a planar parallel gear motor with two pairs of gear meshes, at least one pair of teeth in each sub-motor is engaged at each moment, and the output speed and torque ripple condition depend on the two sub-motor meshes. The phase change of the dot pitch. If the phase changes of the two sub-motor meshing pitches are different, the instantaneous output rotational speeds of the two sub-motors and the maximum and minimum values ​​of the torques may alternately appear, and the result of superimposition may greatly reduce the pulsation.
The calculation formula of the pulsation rate (non-uniformity coefficient) of the gear motor output speed and torque is the same as that of the external gear pump. The structure of the planar parallel gear motor is basically the same as that of the second driven wheel type compound gear pump. The working principle is reversed, and the magnitude and phase change of the meshing point moment are also the same. Therefore, the motor outputs the rotational speed and the uneven coefficient of the torque. The calculation formula should also be the same as the calculation formula of the flow pulsation coefficient of the two driven wheel type compound gear pump with the same structure (the same conclusion can be obtained by detailed analysis). The phase change due to the meshing point distance depends on the number of teeth. The following are discussed in the case of odd and even teeth.
(1) When the odd-numbered teeth (z=2k±1, the integer of k≥7), the phase of the change of the meshing point is different, and the maximum and minimum values ​​of the output speed and torque of the two sub-motors alternately appear, and the superimposed result makes the output The range of extreme values ​​of speed and torque is reduced, and the pulsation rate is reduced. The unevenness coefficient is =(max-min)/m=Q= 2cos2/16z(9)M=(Mmax-Mmin)/Mm=Q= 2cos2/16z(10) According to the analysis in [2], in the meshing process of the two idle gears on the same side of the torque output gear, the change period of the meshing point moment is reduced by half, and the frequency of change is doubled. The pulsation frequency of the output speed and torque is also doubled.
When taking z=17, it is calculated by equations (9) and (10) = M=3.2, while the ordinary gear motor is at z=17, =M=12.6. It can be seen that in the case of odd-numbered teeth, the gear motor The pulsation rate of the output speed and torque is reduced by about 3/4, and the pulsation frequency is doubled, and the quality thereof is significantly improved. Therefore, when designing such a gear motor, the number of gear teeth should be selected as an odd number.
(2) Even-numbered teeth (z=2k, k≥7 integer), the phase change of the meshing point moment is the same, the maximum and minimum values ​​of the output speed and torque appear simultaneously, and the output speed and torque ripple (including the size and Frequency), the same as the ordinary gear motor, the calculation formula is the same.
That is, in the case of even teeth, the pulsation of the motor output speed and torque is not improved, and the quality is still poor.
3 Conclusions (1) When the number of teeth is the same, the displacement, average torque and instantaneous torque of the motor are doubled, thereby increasing the power density of the motor and the axial dimension is also small, which is beneficial in some spaces. Used in the occasion.
(2) The torque output gear is subjected to radial force balance; when the output torque is the same, the radial force of the idler gear is reduced by about half, which improves the stress state of the gear shaft and the bearing, reduces the wear and improves the motor. Work reliability.
(3) Through the appropriate matching teeth (odd teeth), the pulsation rate of the instantaneous output speed and torque of the motor can be significantly reduced, the pulsation frequency can be improved, and the output quality of the gear motor can be improved.
(4) When the number of teeth is equal, the output speed of the motor is low, and the output torque is large, which can improve the starting performance.
Therefore, the motor has the characteristics of simple structure and superior performance, and has high promotion and application value.