The flow fluctuation quality is mainly reflected in the fluctuation coefficient. The smaller the fluctuation coefficient is, the better the quality is. The example parameters of gear micropump are as follows: high speed of 4000 R / min, Pi of 1.1 MPa, Po of 1.6 MPa, modulus of 1, Z of 10, coefficient of addendum height of 1.1, coefficient of tip clearance of 0.15, pressure angle of 20 °, α ‘of 29.5 °, CZ of 0.01, 0.02 mm, μ of 0.00018 PA · s, ultra-low viscosity of krz of 0.15.
The 3D feature of the unloading surface is generated from the 3D model of the gear pair and the unloading groove, and then the double end unloading area is obtained by the area measurement tool of the 3D feature.
Three schemes a, B and C are used to implement different trapped oil pressures. Among them, a adopts single end unloading area and CZ = 0.01 mm; B uses double end unloading area and CZ = 0.01 mm; C uses double end unloading area and CZ = 0.02 mm; corresponding trapped oil pressure is shown in Fig. 1a.
The instantaneous flow rate is shown in Fig. 1b. Among them, δ ‘q = 0.26, δ Q (a) = 0.40, δ Q (b) = 0.41, δ Q (c) = 0.41; ave (qxy) = 4.8 L / min, ave (QSH) of a, B, C are 4.0, 4.0, 3.9 L / min, respectively. If a was taken as the comparison benchmark, the average value of B was reduced by 0.042%, the quality was reduced by 2.44%; the mean value of C was reduced by 3.71%, but the quality was improved by 32.7%.
The results show that: the average flow rate is always less than the theoretical mean value, and the actual fluctuation is always greater than the theoretical fluctuation; simply increasing the unloading area to relieve the trapped oil pressure has almost no effect on the average flow rate and fluctuation coefficient, which is determined by the symmetrical arrangement of double rectangular unloading grooves; The axial gap is the biggest factor affecting the trapped oil pressure, which is contrary to the conventional gear oil pump, which is mainly based on groove unloading and supplemented by axial gap. Therefore, in order to meet the different requirements of large and small axial gaps for oil trapping and unloading and reducing pump leakage, different stepped gaps can be used in axial direction, that is, in the “BG × Hg” axial sealing area between the double rectangular unloading grooves in Fig. 1, an additional gap C0 as shown in Fig. 2 is sunk. At this time, the axial gaps of leakage and trapped oil unloading are CZ, CZ + C0 respectively.
According to scheme C in Fig. 1a, it is shown that as long as CZ + C0 > 0.02 mm, that is, C0 ＞ (0.02-cz) mm, it can meet the needs of trapped oil unloading. Among them, the best axial gap is 0.0012 mm, which is difficult to achieve in the actual processing and assembly. Therefore, CZ should be determined by the accuracy of actual machining and assembly. When CZ > 0.02 mm, C0 = 0; otherwise, C0 = 0.02-cz.