m2=5mm,Z1=18,Z2=61,Z3=19,Z4=68,b1=52mm,b2=88mm,512=0.94, 534=0.48,axis distance 4=122.5mm.In this case the allowed loading ability is 19.7kW for the high speed stage and 19.6kW for the low speed stage.The error of the equal strength is 0.5%.As shown in Fig,7(b)there is only 7.5kW for tradational design. D=50mm =9061/mm i=12.56 Out meshes 30 Constraints of 3n2 cylinders 20 21,17n1,5 diameter 10 In meshes 0 110120130 T140 A/mm (a) (b) Fig.7 Gear drive of gear-cylinder of TDC a)Sketch of the drive b)Design point location of the optimal and tradational design 5 Conclusion A Summary of some results of our research in the discrete variable opti- mization have inducted above.It is noteworthy pointed out that the package MOD is generally a very effective way to solve the discrete variable problems. At present,the package MOD has been applied successfully to mechanical engi- neering,reliability engineering,city water engineering and economic develop- ment planning and other areas. References 1 Siddall J N.Optimal Engineering Design (Principles and Applications). Marcel Dekker,1982 2 Reklaitis G V.Engineering Optimzation (Methods and Application).Joh Wiley and Sons,New York,1983 3 Chen Lizhou,et al.Optimal Design for Mechanical Engineering.Sha- nghai Science and Technology Press (in China),1982 4 Chen Lizhou,et al,Mixed Discrete Variable Optimization for Enginee- ring Design (Priciles and Application).Mechanical Industry Press,1990 5 Chen Lizhou,J of CMES,1985,21(2):179 6 Chen Lizhou,et al.J of Beijing University of Iron and Steel Technolo- gy,1987,9(3):65 7 Chen Lizhou,et al.I of Beijing University of Iron and steel Techno- 1ogy,1987,9(4):73 347， ， ， ， 二 ， 二 ， ， ， 考 ， 。 ， 古 ， ， 。 。 ， 月 二 口 取 士 三 〕 一 公 五 宜 宜 呈 五 。 ， ， ， 几 、 ， ， ， ， ， 。 。 。 ， ， 飞 又 。 ， ， ， ， ， ， ， 。 ， ， 口九︸