Agricultural tractors - Test procedures - Part 2: Rear three-point linkage lifting capacity
1Key Takeaways
This document specifies test procedures for determining the lifting capacity of rear-mounted threepoint linkage systems: a) the maximum vertical force which can be exerted by the hydraulic lift at the lower hitch points throughout their full range of movement; b) the maximum vertical force which can be exerted by the h…
2Expert Interpretation
An in-depth analysis of the ISO 789-2:2018 standard for testing the lifting capacity of a tractor's rear three-point hitch system, including test conditions, measurement procedures, and reporting requirements, including specifications for hydraulic system performance evaluation and comparative testing.
Analysis of the core content of the standard
The fourth edition of ISO 789-2:2018 replaces the third edition of 1993, and its technical content is coordinated with OECD Code 2:2017. The standard mainly specifies two types of tests:
| Test type | Measurement points | Key parameters |
|---|---|---|
| Lifting force of lower suspension point | Horizontal rod of lower hinge point | Vertical force at 6 equidistant measuring points |
| Lifting force of coupling frame | Resultant force at the center of gravity of the frame at 610mm behind the hinge point | The resultant force is |
Key technical requirements
Hydraulic system specifications
During testing, the hydraulic oil temperature must be maintained at 65 ± 5°C (65 ± 5°C). The pressure gauge should be installed at the tractor's external port. The final report data must be corrected to 90% of the hydraulic system safety valve set pressure.Measurement accuracy control
- Force measurement error ≤ 1%
- Displacement measurement error ≤ 0.5%
- Pressure measurement error ≤ 2%
Test implementation points
According to the requirements of Chapter 5 of the standard, the tested tractor should:
- Complete the running-in period specified by the manufacturer (the running-in location and duration must be indicated in the report)
- The viscosity of the hydraulic oil complies with the classification of ISO 3448:1992
- The ambient temperature is maintained within the range of 23±7°C
Standard evolution analysis
Main updates of the 2018 version:
- Added applicable instructions for the three-point mechanism of the front suspension
- Specify that the test report must include rear axle torque calculations.
- The number of measurement points has been clarified from "several" to at least 6
Typical Application Case
Tests on a certain model of John Deere 6M tractor showed that, under the ISO 730 Category 2 suspension configuration, the corrected maximum lifting force at 610mm was 12.5kN, corresponding to a hydraulic system working pressure of 18MPa.
Implementation Recommendations
1. Prioritize the combination of measurement points specified by the manufacturer.
2. Verify that the full travel angle of the three-point suspension is ≥10° before testing.
3. The report should include a declaration of conformity to OECD Code 2.