1 Scope
This document specifies the performance requirements and test methods for a descent control device, which is fitted to the boom, intermediate boom and bucket bar hydraulic cylinders of hydraulic excavators and backhoe loaders, to control the rate of descent of the boom in the event of failure or rupture of the hydraulic lines.
This document applies to the lowering control device (fitted with the standard linkage mechanism specified by the manufacturer) for the lifting of objects in the backhoe unit of hydraulic excavators and backhoe loaders. On machines supplied with an alternative linkage mechanism, only the standard length specified by the manufacturer is tested.
2 Normative references
The contents of the following documents constitute essential provisions of this document by means of normative references in the text. Where a reference is dated, only the version corresponding to that date applies to this document; where a reference is not dated, the latest version (including all amendment sheets) applies to this document.
ISO6165 Earth moving machinery - Basic types - I-identification and terms and definitions
Note 1: GB/T 8498-2017 Basic Type Identification Terms and Definitive Document of Earth moving Machinery (CISO 6165:2012. IDD)
ISO9248 Earth moving machinery Units for dimensions, performance and capacities and their measurement accuracy
Note 2: GB/T 21153-2007 Earth moving machinery - Units and measurement accuracy of dimensional properties and parameters (ISO 9248: 1992, MOD)
3 Terms and definitions
The terms defined in ISO 6165 and the following terms and definitions apply to this document.
3.1
linkage control system
The hydraulic control components (including pilot servo valves) for lifting and lowering lifting points in the case of object lifting.
3.2
Lifting linkage
The combination of components used to lift and lower the lifting point during the lifting of an object, e.g. the combination of a moving arm and a bucket bar.
3.3
Lowering control device
A hydraulic control valve for controlling the lowering of the linkage in the event of failure or rupture of the hydraulic line.
3.4
Failure-simulating device
Hydraulic valve unit for simulating the failure or rupture of a hydraulic line in the control system of a linkage mechanism.
3.5
Signal line
Hydraulic circuit used to detect pressure.
4 Descent control device requirements
4.1 The descent control device shall comply with the requirements of 4.1.1 ~ ~ 4.1.8.
4.1.1 The lowering control shall operate automatically when the hydraulic cylinders in the control system of the linkage mechanism that holds the load in the lifting position are pressurised even if the machine/ignition is switched off.
4.1.2 The operation of the lowering control shall not impair the normal response of the machine in normal operation and shall not affect the stability of the machine at any time.
4.1.3 A relief valve may be fitted between the hydraulic cylinder and the descent control to protect the hydraulic cylinder.
4.1.4 In the event of failure of the control system of the linkage mechanism, the load should be dropped in such a way as not to cause injury to personnel or to affect the stability of the machine as far as possible.
4.1.5 The following devices shall be securely attached to each hydraulic cylinder in the linkage control system that holds the load in the raised position:
a) the lowering control and the associated hard pipes and fittings between the lowering control and the hydraulic cylinder (hoses are not applicable);
b) where a separate relief valve (see 4.1.3) and the associated hard pipes and fittings are provided, they are connected in parallel with the control unit.
The minimum breaking pressure for the hard pipes and fittings used to connect the control valve and the relief valve provided in parallel with the hydraulic cylinder should be four times the working circuit pressure of this part of the system.
4.1.6 When there is a signal line, the leakage volume of each hydraulic cylinder should not exceed 10 L/ min at the specified working circuit pressure when the oil temperature is 40 °C~50 °C, if one of the lines in the signal line is broken.
4.1.7 If there is a compensating oil circuit between hydraulic cylinders, a rupture in one of the oil circuits will result in:
-For machines with a working mass (specified in GB/T 21154) of less than 40 t, the leakage amount of each hydraulic cylinder should be less than 10 L/min at the specified working circuit pressure when the oil temperature is between 40 °C and 50 °C;
For machines with working mass (as specified in GB/T 21154) greater than or equal to 40 t, under the specified working circuit pressure, when the oil temperature
5 Test methods
5.1 Apparatus and equipment
5.1.1 Apparatus for measuring the variation of displacement in the vertical plane with time, a ruler and a stopwatch may be used. The accuracy of the measurement shall be in accordance with the provisions of ISO 9248.
5.1.2 Thermometer or equivalent temperature measuring device, the measurement range is 0 ℃ ~ 100 ℃, the accuracy of ± 1 ℃.
5.1.3 The oil collection tank or the oil return pipe of the tank used to collect the hydraulic oil, either one of the two.
5.2 Test preparation
5.2.1 The test and recording method should ensure repeatable and reproducible results (e.g. video recording with a fixed background scale).
5.2.2 In the case of a linkage control system where failure would cause the lifting linkage to fall without a fall control device installed, a failure simulation device should be installed in the hydraulic line.
Examples of installation are as follows:
a) The oil circuit between the hydraulic cylinder and the control valve, as shown in Figure 1;
b) The signal line between the hydraulic cylinder and the monitoring test device (pressure sensor) installed on the machine, as shown in Figure 2;
c) the compensation oil circuit between the hydraulic cylinders, as shown in Figure 3.
The failure simulator may be required to run several tests at different locations. For example:
Failure simulation test of the oil circuit between the hydraulic cylinder and the control valve [see column a) above];
Failure simulation of the compensation circuit between the hydraulic cylinders [see item c) above].
5.3.2 Internal leakage test
The lowering control is in the neutral position.
The vertical rate of load drop caused by internal leakage in the system should not exceed 10 mm/s.
5.3.3 Your holding position test
The test load shall be placed at such a height that the test load does not come into contact with the ground during the test. When the descent control device is in the neutral position, open the failure simulation device.
Measure the total amount of load drop during the initial 10 s; this should not exceed 100 mm.
5.3.4 Lifting process test
The test load shall be placed at such a height that the test load does not come into contact with the ground during the test. The test load shall be lifted smoothly and continuously without impact (see 5.3.1).
The failure simulator shall be switched on during the lifting process and the position of the drop control shall remain unchanged. The total amount of load drop during the initial 10 s is measured; this should not exceed 100 mm.
5.3.5 Drop test
The test load shall be placed at such a height that the test load does not come into contact with the ground during the test. The test load shall be lowered smoothly and continuously without impact (see 5.3.1).
Turn on the failure simulator. The following can be measured simultaneously or separately. If measured separately, the two initial descent velocities shall be measured in accordance with 5.3.1.
a) Without changing the position of the descent control device, measure the increment of descent speed. In a period of not less than 2 s, the increase in the speed of descent of the test load shall be less than the average initial speed.
The increase in speed should be less than 100% of the average initial speed.
b) Measure the total drop of the load after the drop control has been moved to the neutral position. The lowering control shall be capable of limiting the movement of the arm so that the total drop in load does not exceed 100 mm in the first 10 s after the lowering control has been moved to the neutral position.
5.3.6 Your compensation oil circuit or signal oil circuit test
5.3.6.1 The test shall be carried out without load.
5.3.6.2 The linkage shall be raised to the position shown in Figure 4 and the lowering control moved to the neutral position.
5.3.6.3 Turn on the failure simulator.
5.3.6.4 If a hydraulic cylinder compensation or signalling line exists, the line shall be designed in accordance with the acceptance guidelines for compensation or signalling lines as specified in 4.1.8 or the hydraulic cylinder compensation or signalling line shall be protected by a descent control. All descent control devices installed in the hydraulic cylinder compensation or signalling line shall be tested in accordance with this document.
Bibliography
contents
1 Scope
2 Normative references
3 Terms and definitions
4 Descent control device requirements
5 Test methods
Bibliography
