Sowing depth stability analysis and test verification of no-tillage planter parallel 4-bar row unit

The sowing depth stability and consistency of the no-tillage planter, particularly the high-speed operation, are poor. A reason for this is that the structure and parameter selection of no-tillage planter row unit profiling mechanism are unreasonable. The stability and consistency of sowing depth is beneficial when the upper and lower links of the parallel 4-bar profiling mechanism (PFPM) are parallel to the ground, but this principle is not satisfied on the uneven no-till soil. To improve the stability of gauge wheels downforce (GWD) and sowing depth of no-tillage planter row unit. The variation law of spring additional downforce (SAD) with tilt angle of parallel 4-bar profiling mechanism (PFPM) and connection offset of spring is discussed by constructing the steady state analysis matrix equation of PFPM. Additionally, the influence of tilt angle of PFPM and SAD on the stability of the sowing depth was analyzed. Based on the single factor control variable test method, bench and field tests were conducted. The test results show that the SAD increases nonlinearly with the increase in the degree of tilt of PFPM from downward to upward. Under the condition that four springs are installed and the tilt angle of PFPM is between (−20°–20°), the maximum SAD is 485.95 N, 1236.64 N, and 2258.05 N when the spring connection offset is 44 mm, 79 mm, and 115 mm, respectively. When the tilt angle is 8° upward, the GWD increases by 429 N, 575 N, and 984 N, GWD stability increases by 42.31 %, 56.16 %, and 50.29 %, and ditching depth stability increases by 30.00 %, 12.50 %, and 30.00 % compared with that of the control group at the sowing speed of 8, 10, and 12 km/h, respectively. At the sowing speed of 10 km/h, when the PFPM is operated with spring-free and additional springs, the average GWD increases by 353 N, and the stability of GWD and ditching depth increases by 34.38 % and 20.00 %, respectively. The results showed that the tilt upward of PFPM and SAD were beneficial to improve the stability of the GWD and sowing depth of the no-tillage planter row unit. The results not only verify the correctness of theoretical analysis, but also provide theoretical basis for the design and application adjustment of high-speed no-tillage planter.