The main sources are mechanical impurities that remain in the hydraulic system after cleaning, such as rust, cast sand, welding slag, iron filings, paint and cotton yarn, etc. External impurities entering the hydraulic system, such as through the oil filler entrance and dust entering at the scraper seal. Impurities generated during the working process, such as debris formed by the hydraulic action of the seal, metal powder generated by relative wear and movement, colloid, asphaltene, carbon residue, etc. Due to oxidative deterioration of the oil.
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In July 2011, a total of 127,210 micro-producers were produced nationwide, a decrease of 9.19% month-on-month and a decrease of 23.51% year-on-year. 125,998 micro-customers were sold, a decrease of 16.76% from the previous quarter and a year-on-year decrease of 16.24%. From January to July 2011, 1,298,193 units were accumulatively produced, a cumulative decrease of 10.50% year-on-year, and cumulative sales of 1,313,301 were down 10.49% year-on-year.
Judging from the July production situation, the top five companies are: SAIC-GM-Wuling Automotive Co., Ltd., Chongqing Changan Automobile Co., Ltd., Nanjing Changan Automobile Co., Ltd., Dongfeng Motor Corporation, and Haima Business Automobile Co., Ltd. Monthly sales were: 63142, 24138, 8966, 8409, 4683, and a total of 109,338 vehicles were sold by the five companies, which accounted for 85.95% of the total sales of micro-corporate companies. 
From January to July 2011, the top five companies are: SAIC-GM-Wuling Automotive Co., Ltd., Chongqing Changan Automobile Co., Ltd., Dongfeng Motor Co., Ltd., Nanjing Changan Automobile Co., Ltd., and Hafei Automobile Co., Ltd. Co., Ltd., cumulative production were: 605454, 214830, 145331, 100139, 50992 vehicles. The five companies accumulatively produced 1,116,746 vehicles, which accounted for 86.02% of the cumulative total production of micro-enterprises.
Sales
Judging from the July sales situation, the top five companies are: SAIC-GM-Wuling Automotive Co., Ltd., Chongqing Changan Automobile Co., Ltd., Dongfeng Motor Co., Ltd., Nanjing Changan Automobile Co., Ltd., and Haima Commercial Vehicles Co., Ltd. Monthly sales were 69145, 17506, 8883, 8770, and 4971, respectively. Five companies sold 109,275 units, accounting for 86.73% of the total micro-car sales.
From January to July 2011 sales: The top five companies are: SAIC-GM-Wuling Automotive Co., Ltd., Chongqing Changan Automobile Co., Ltd., Dongfeng Motor Co., Ltd., Nanjing Changan Automobile Co., Ltd., and Hafei Motors Co., Ltd. Co., Ltd., cumulative sales were: 638533, 221339, 143212, 108015, 51176 vehicles. A total of 1,162,275 vehicles were sold by the five companies, which accounted for 87.32% of the cumulative sales of micro-enterprises.