1、 WORLDWIDE ENGINEERING STANDARDS General Specification GMW15867 Pressure Relieve Devices for Low and High Pressure Side Copyright 2013 General Motors Company All Rights Reserved June 2013 Page 1 of 1 1 Introduction Note: Nothing in this standard supercedes applicable laws and regulations. Note: In t
2、he event of conflict between the English and domestic language, the English language shall take precedence. 1.1 Scope. Pressure relieve device is for use in all passenger car and light commercial vehicle air conditioning (A/C). 1.2 Mission/Theme. This standard defines the minimum requirements for pr
3、essure relieve devices of the passenger car air conditioning system (not valid with/for R744 heating system) which are operated with refrigerant R744. The pressure relive devices cause a refrigerant blow-off from the car air conditioning system in any event of a system over pressure. 1.3 Classificat
4、ion. Not applicable. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. DIN 8964 ISO 9001 ISO 9227 SAE J639 DIN 50014 2.2 GM Standards/Specifications. GMW3059 GMW3116 GMW15786 2.3 Additional References. None. 3 Requ
5、irements 3.1 System/Subsystem/Component/Part Definition. 3.1.1 Appearance. All exterior and interior surfaces shall be clean and free of manufacturing lubricants, flux, soluble flux residue, metal chips, scale, and other contaminants that are not associated with the function. Flux residue shall not
6、be considered a contaminant if it is insoluble in water, R744 or PAG/POE oil and does not contribute to corrosion in the system. Appearance and finish of parts shall be free of weld and/or braze splatter, flash, ridges, roughness and of tool lubricants and other contamination according to DIN 8964.
7、3.1.2 Content. The major function of the pressure relieve device in the R744 A/C system is to protect the components and the A/C system from exceeding the maximum pressure. While current R134a refrigeration systems have mostly one pressure relieve device on the high pressure side in the compressor,
8、two pressure relieve devices shall be provided on both the high pressure and low pressure sides of R744 refrigeration systems respectively, per SAE J639 and German Vehicle Development Authority (VDA) safety concept. The main reasons for exceeding the maximum pressures are due to either refrigerant o
9、verfill of the refrigerant circuit, or malfunctions of the compressor control or blocking of a component, e.g., evaporator. 3.1.2.1 Physical Content. The pressure relieve device shall provide sealing to refrigerant R744. Sealing and function shall be designed for vehicle life time. Refrigerant flow
10、out from the pressure relieve device shall be planned and executed carefully to assure that the refrigerant can escape from the system with the lowest possible risk. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking
11、permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW15867 Copyright 2013 General Motors Company All Rights Reserved June 2013 Page 2 of 2 3.1.2.2 Functional Content. Two fundamental functional types of pressure relieve devices are possible for the refrigerant circuit with R7
12、44: The self-closing reversible relief valve which closes itself and, consequently, the refrigerant circuit automatically and tightly after each overpressure incident, and The irreversible burst device which responds once. The entire refrigerant inside the A/C system with part of the lubricant is di
13、scharged to the environment and the A/C circuit remains open to the environment. The probability that the pressure relieve device on the low pressure side responds is much lower than a response of the high pressure side. Usually the excessive operating pressure on the low pressure side is caused by
14、a significant overfill or blocking behind the burst device, e.g., evaporator. On the high pressure side excessive operating pressure is caused by malfunction of high pressure limitation of the compressor. Each pressure relieve device shall operate automatically. No other methods by mechanical, therm
15、ostatically and electrical control are allowed to use for the activation of the pressure relieve device. The most important differences between the relief valve and the burst device are: Lower component strain than by explosive decompression because normally the system is not completely emptied to a
16、mbient pressure level. Because the relief valve closes at a certain pressure, the system normally never runs without refrigerant. The noise level in case of relief valve response relative to burst device response is lower. The function of the relief valve shall be tested without damaging the relief
17、valve. 3.1.3 Ambient Environment and Operating Conditions. This defines the ambient temperatures and refrigerant temperatures which the components are exposed to. As orientation, the following values are defined for operating and non-operating A/C system. If the A/C system is switched off, the ambie
18、nt conditions are equal to environment temperatures which are relevant for the design and construction of the pressure relieve devices. 3.1.3.1 High Pressure Side. The pressure relieve device shall be mounted directly in the compressor as part of the compressor assembly. Due to the typical location
19、of the compressor near the hot engine, the environmental temperatures are in the range of: -40 C in switched off condition and/or, -12 C during refrigeration system operation to +130 C permanent to +150 C short term (5 minutes maximum each for a total of 168 h). For special application - extremely h
20、ot that shall be defined by GM: -40 C in switched off condition and/or -12 C during refrigeration system operation to +150 C permanent to +180 C short term (5 minutes maximum each for a total of 168 h). The refrigerant temperature during operation is between -12 C to +165 C and +180 C short term (5
21、minutes maximum each for a total of 168 h). 3.1.3.2 Low Pressure Side. The pressure relieve device shall not be located near the hot engine or other heat source underhood, therefore, the environmental temperatures are in the range of -40 C in switched off condition and/or -12 C during refrigeration
22、system operation to +120 C permanent to +135 C short term (5 minutes maximum each for a total of 168 h). The refrigerant temperature during operation is between -12 C and +80 C. 3.1.4 Interfaces. 3.1.4.1 High Pressure Side. Pressure relieve devices shall in principle be integrated in the system dire
23、ctly or close to the pressure source. The relief valve and/or the burst device on the high pressure side are, therefore, part of the compressor. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without lic
24、ense from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW15867 Copyright 2013 General Motors Company All Rights Reserved June 2013 Page 3 of 3 3.1.4.2 Low Pressure Side. Additionally, another pressure relieve device shall be provided on the low pressure side because of the maximum operating pressure
25、on the low pressure side. In compliance with SAE J639, overpressure by overcharging and also by blocking shall be avoided. Therefore, the relief valve or burst device on the low pressure side shall be located upstream directly after the expansion device and before the evaporator. 3.1.4.3 Non-interch
26、angeability. The pressure control devices for high and low pressure side are not allowed to interchange one another. Therefore, the outside design of the pressure control elements shall be so different that mismatch is impossible. A metric fine left thread shall be used for high pressure side with s
27、ize M12x1, and for low pressure side with size M14x1. A hexagonal bolt head without thread marking is required. 3.1.4.4 No Cross Section Reduction. When installing the pressure relieve devices in the respective A/C pipe and compressor, the detail dimensions of the interface shall be reviewed careful
28、ly to ensure that the end plugged into the line and the housing of the compressor does not negatively influence the flow cross section of the medium. The reduced cross section of the flow path will cause pressure losses. Such pressure losses are not allowed for the normal function of the pressure re
29、lieve device. 3.1.5 Safety and Usage Definition. The installation location of both pressure relieve devices shall be selected to assure that refrigerant blow-off is outside the passenger compartment including A/C unit, air intake and luggage compartment. Additionally, the installation locations and
30、blow-off directions of the pressure relieve devices shall be such that personal injury of persons near the vehicle and the system is not possible in case of refrigerant blow-off. The burst sound level shall be such that no personal injury of persons near the vehicle and the system is possible. The i
31、ntegration of the pressure relieve devices into a third component, e.g., expansion device or connector block, shall be in such a way that the pressure relieve devices are from the outside of the component removable. To avoid the pressure relieve device being opened replaced inappropriately, e.g., th
32、rough a screw, a warning is required on the pressure relieve device. The warning shall say for example “Do Not Remove”, or the corresponding ISO symbol shall be used. 3.2 Product Characteristics. The test temperature for the following physical tests is +23 C 5 C according to DIN 50014 unless otherwi
33、se specified. A minimum of five test samples are required for each test. The test results shall be documented as part of Production Part Approval Process (PPAP) documents to GM. 3.2.1 Performance Requirements. The minimum pressures at which the pressure relieve devices shall respond at the earliest
34、are: 15 MPa on the high pressure side (HD). 11 MPa on the low pressure side (ND). Pressure relief devices shall open completely and prevent the pressure in the refrigerant circuit from increasing further. 17 MPa on the high pressure side (HD). 13 MPa on the low pressure side (ND). The response press
35、ure (RP) intervals of the pressure relieve devices are: 15 MPa 10 actuations, the leak rate may increase to 2 g/year maximum. Repeated leak rate test: The repeated leak rate test is made under the load condition No.3 and shall be used for the single and series tests which will be defined later. The
36、leak rate determined according to Appendix A, Table A1 and Table A2 (at a standstill +30 C and a system pressure of 7 MPa) is defined as the base leakage for the pressure relieve device. This value shall not be exceeded during all repeated leak rate tests. The tolerance is set to 20%. The load condi
37、tion shall be maintained for 48 h according to this paragraph. 3.2.1.2 Resistance to Under Pressure/Vacuum. The pressure relieve devices shall be installed according to paragraph 3.2.1.1 in test blocks which are completely sealed to the environment by soldering. A vacuum of 0.5 kPa absolute shall be
38、 applied to the pressure relieve devices and maintained constant for 5 minutes. The allowed pressure increase shall not exceed 0.5 kPa within 30 minutes and with pump switched off. The pressure relief device shall function properly after this test. After this test, the leak rate test, according to p
39、aragraph 3.2.1.1, shall be repeated. The under pressure resistance test with leak rate test shall be performed subsequently 3 times. 3.2.1.3 Response Pressure Test. The response pressure for high pressure side shall be tested at: 15 MPa at +200 C 24 h at +100 C Zn Ni: 24 h at +150 C Salt Spray Test
40、Salt solution: 42 g/l NaCl Acetic acid: 10 g/l pH value of condensate: 2.8 to 3.0 Temperature: +50 C Cycle (2 h) composed of: 30 minute spray 90 minute rest Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted
41、 without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW15867 Copyright 2013 General Motors Company All Rights Reserved June 2013 Page 14 of 14 Table A4: Alternating Climatic Corrosion Test According to ISO 9227 Alternating Climatic Corrosion Aging: Zn Fe: 24 h at +100 C Zn Ni: 24 h at +
42、150 C Salt Spray Test Salt solution: 40 g/l NaCl Salt solution: 10 g/l CaCl2l pH value of condensate: 6.5 to 7.2 Temperature: +35 C Week Cycle 5 days = 5 x 24 h corrosion 4 h spray 4 h cool down to +23 C 5 C 16 h store at +40 C/100% relative humidity 2 days = 4 x 12 h alternating climatic 2 h cool d
43、own 4 h store at -40 C 2 h warm up 4 h store at + 80 C A1 Statistical Evaluation and Interpretation Test procedure, statistical evaluation and interpretation to ensure that the low pressure burst device meets the pressure response requirements with respect to the opening pressure over a certain temp
44、erature range in production process. The statistical evaluation of this test procedure is based according to ISO 9001 standard. Specification of the analysis of a test procedure for proofing that the opening pressure stays within the critical specification limits (LSL = 11.0 MPa/USL = 13.0 MPa) for
45、temperatures ranging from +30 C to +120 C. (LSL/USL = lower/upper specification limit): It is presumed that the mean opening pressure changes monotonic with changing temperature (the higher the temperature, the lower the opening pressure). For this reason, it shall be determined that the opening pre
46、ssure stays within the standard limits for the highest (+120 C, see paragraph 3.2.1.3) as well as for the lowest relevant temperature (+30 C, see paragraph 3.2.1.3). In order to verify the capability of the process, both temperatures need to be tested individually. For each temperature, a sample siz
47、e of 125 pieces shall be tested to ensure statistical relevance. On the basis of these tests, the mean value of the opening pressure shall be determined according to Eq 1 for each temperature separately. The standard deviation shall be determined likewise for each temperature according to Eq 2. Usin
48、g these values for the mean opening pressure and its standard deviation, one has to determine the process capability indices Cp and Cpk using Eq 3, (for details refer to QS 9000, as part of ISO 9001) and the specification limits LSL=11.0 MPa and USL=13.0 MPa. For the determined capability indices, t
49、he following limits shall be reached: Cp 2.0 and Cpk 1.67 A Cpk value of 1.67 corresponds to 1 ppm out of the specification limits, see Table A6. In Figure A1 the estimated normal probability distributions for the qualitatively expected results of the tests are depicted. The numerical values used to generate this plot are provided in Table A5. (Note these are just estimated numbers to illustrate what kind
