Tham khảo tài liệu 'manual gearbox design part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Internal running gear 21 driving gear can be fixed. Knowing the number of teeth on this smallest gear the lowest gear ratio can be calculated and plotted on the road speed engine revolution graph. Knowing the highest and the lowest gear ratios with the total number of teeth then all the intermediate ratios possible between these two gears can be calculated using the same parameters that were used to calculate the highest and lowest ratios. These intermediate ratios should now be plotted on the road speed engine revolution graph and finally a line should be drawn across the graph at the maximum engine revolutions per minute to be used this is usually slightly higher than the revolutions at which the engine produces maximum torque. Utilizing this graph the selection of the gear ratios can be commenced by using the maximum speed required in first gear then the ratio can be marked and from the point that this intersects the maximum engine revolutions line a vertical line should be drawn on the graph. The torque ranges of the types of engine the transmission is being designed for will permit a point to be fixed on this vertical line at the engine revolutions for maximum torque and at this point the nearest calculated intermediate gear line should be marked on the vertical line . the mark should be within the engine usable torque range. This vertical line represents the fall in engine revolutions per minute when changing down from second gear to first gear. Using the point where the vertical line crosses the maximum torque line and joining this with the point on the engine maximum revolution horizontal line coinciding with the maximum road speed required will provide a guide-line for the bottom points of other intermediate ratios. The ratio nearest to but above the minimum engine revolution torque band-line must be used as the first approximation for second gear unless second gear has to be fixed to meet some specific target such as zero to a given miles per hour .
